BeppoSAX observations of a new X-ray burster in the Galactic Center region, possibly coinci

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Radio Observations of Masers in Post-AGB Stars

that the far-infrared colours provide a powerful tool for distinguishing between early and late, and low and high mass, post-AGB objects.
The present project is to observe maser emission from hydroxyl (OH), water (H2O) and silicon monoxide (SiO) molecules that are located in the outﬂowing stellar winds. Each molecule exists in diﬀerent physical conditions and the maser emission from these molecules is produced at diﬀerent locations within the circumstellar winds, providing information on the wind velocities, and on whether the winds are likely to be spherically symmetrical or distorted.
4. Results
Figure 1 shows examples of maser spectra for sources in our sample. We have classiﬁed them in six diﬀerent categories, as follows. Many exhibit a doublepeaked spectrum (D) with steep outer edges and sloping inner edges between the two peaks. This spectral proﬁle is characteristic of an expanding spherical shell, with the strongest emission coming from the region of the shell closest and furthest from the observer along the line of sight (Reid et al. 1977).

Observation of spin-wave characteristics in the two-dimensional ferromagnetic ordering of i

a r X i v :c o n d -m a t /0504155v 1 [c o n d -m a t .m e s -h a l l ] 7 A p r 2005Observation of spin-wave characteristics in the two-dimensional ferromagneticordering of in-plane spinsM.K.Mukhopadhyay 1,M.K.Sanyal 1,T.Sakakibara 2,V.Leiner 3,R.M.Dalgliesh 4,and ngridge 41Surface Physics Division,Saha Institute of Nuclear Physics,1/AF,Bidhannagar,Kolkata 700064,India.2Institute for Solid State Physics,University of Tokyo,Kashiwanoha,Kashiwa,Chiba 277-8581,Japan.3Lehrstuhl f¨u r Experimentalphysik,Ruhr-Universit¨a t Bochum,D44780Bochum,Germany.4ISIS,Rutherford Appleton Laboratory,Chilton,Didcot,Oxfordshire OX110QX,UK(Dated:February 2,2008)The role of dipolar interactions and anisotropy are important to obtain,otherwise forbidden,ferro-magnetic ordering at ﬁnite temperature for ions arranged in two-dimensional (2D)arrays (monolay-ers).Here we demonstrate that conventional low temperature magnetometry and polarized neutron scattering measurements can be performed to study ferromagnetic ordering of in-plane spins in 2D systems using a multilayer stack of non-interacting monolayers of gadolinium ions.The spontaneous magnetization is absent in the heterogenous magnetic phase observed here and the saturation value of the net magnetization was found to depend on the applied magnetic ﬁeld.The net magnetiza-tion rises exponentially with lowering temperature and then reaches saturation following a T ln(βT )dependence.These ﬁndings verify predictions of the spin-wave theory of 2D in-plane spin system with ferromagnetic interaction and will initiate further theoretical development.PACS numbers:75.70.Ak,75.60.Ej,75.50.XxFerromagnetic materials conﬁned in ultra-thin ﬁlms and multilayered structures are being studied extensively for the development of high-density magnetic data stor-age devices and to reﬁne our basic knowledge in low-dimensional physics [1,2,3,4].Recent advances in growth techniques such as molecular beam epitaxy and magnetization (M )measurement techniques based on the magneto-optical Kerr eﬀect have enabled us to measure small magnetic signals as a function of applied magnetic ﬁeld (H )and temperature (T )even from one atomic monolayer of a ferromagnetic material and a wide range of ordering eﬀects has been observed [5,6,7,8,9,10].These measurements have also demonstrated the exis-tence of a spontaneous magnetization and have revealed hysteresis curves in two-[5]and one-dimensional [9]sys-tems,where magnetic ions are arranged in a grid or in a line within a monolayer.A recently generalized theorem [3,4]showed,following spin-wave theory,that long-range ferromagnetic order and hence spontaneous magnetization cannot exist at ﬁnite temperature in a two-dimensional systems provided spin-spin interactions are isotropic and short range.A theoretical formalism [7,8,11,12]and computer simulations [6,10]have been developed to include anisotropy and dipolar interactions to explain the apparent contradiction between theory and experiment in low-dimensional systems.A 2D array of magnetic ions with lattice parameter ‘a ’of spins S can be described by a Hamiltonian,H =H ex +H d +H k(1)The strength of the three terms arise from exchange,dipolar and magneto-crystalline anisotropic interactions respectively,and have been approximated by expressing[6,7]these terms in equivalent magnetic ﬁeld units as,2µB H ex =JS ,2µB H d =4παgS ,2µB H k =6KS (2)In the above expression α(∼1)depends on the lat-tice type and g is equal [6]to (2µB )2/a 3.K is the anisotropy constant.The magnetization reduction due to thermally activated spin waves was calculated with this Hamiltonian and one obtains a non-zero temperature for long-range ferromagnetic ordering as a gap of width∆z =2µB H eﬀk opens up at the bottom of the spin wave spectrum for an easy-magnetization axis (z )perpendic-ular to the ﬁlm plane.The easy-magnetization axis is determined by the sign of the eﬀective anisotropy ﬁeld (H eﬀk =H k −H d )deﬁned [7]byH eﬀk =13(3)This explains the observation of hysteresis curves in a monolayer with spins oriented normal to the surface [5,6,9].However,the situation is quite diﬀerent forspins oriented in an in-plane direction with H eﬀk <0as the spin-wave spectrum remains gapless.The long-range character of the dipole interactions was found [11]to be responsible for creating a pseudo-gap ∆xy =(πSg/2)6|K eﬀ|J/(πgT c ))and out-of-plane spins (with β=2K B/∆z=1/T c).Here A=K B/(4πJS2)and M0is the saturation value of the net magnetization that de-pends on theﬁeld applied to carry out measurements [12].Below T c spin wave theory predicts[7]an enhance-ment of M(T)as[1−A exp(−1/(βT))]and[1−CTν] for out-of-plane and in-plane ordering respectively where C depends on∆xy andνexpected[6,7,11]to be3/2. For0<|K eﬀ|<π2g2/(6J)in-plane spins can not stabi-lize in a homogeneous phase as the magneto-crystalline anisotropy becomes large enough to pull some of the spins in the out-of-plane direction and create a ripple like in-stability[6,7].It is known that both the average magne-tization M(T)as well as the initial susceptibilityχ(T)is proportional to the physical extent of the ordered phase l⋆that minimizes the zero-ﬁeld energy[6]and can be written asM∝Hl⋆andχ∝l⋆with l⋆∝exp(−γT)(5) It is expected that at low enough temperature,l⋆reaches saturation either because l⋆becomes comparable to the sample size or due to a freezing of the ripple walls.The net magnetization M(T)of the ordered domains then should follow the spin-wave prediction(Eq.(4))to reach saturation.Here we present the veriﬁcation of this theoreti-cal prediction of2D ferromagnetic ordering of in-plane spins using Langmuir-Blodgett(LB)ﬁlms of gadolinium stearate.The presence of a large multilayer stack of non-interacting monolayers of gadolinium has enabled us to carry out conventional quantitative magnetization mea-surements at sub-Kelvin temperatures.We could also use polarized neutron scattering measurements[13,14], to show that the ordered phase of the in-plane spins is inhomogeneous and that the monolayers remain uncor-related even when the net magnetization reaches a satu-ration value.In the metal-organic structure formed by LB tech-niques[15,16,17],gadolinium ions are separated by ap-proximately5˚A within a monolayer to form a distorted hexagonal2D lattice and the monolayers are separated from each other by49˚A by organic chains(Fig.1).Films having50such monolayers of gadolinium ions were de-posited on1mm thick Si(001)substrates and character-ized using x-ray reﬂectivity technique,as discussed earlier [17].Neutron reﬂection measurements(refer Fig.2)were carried out on the CRISP reﬂectometer at the Rutherford Appleton Laboratory(RAL),UK using a cold,polychro-matic neutron beam[18,19]and at the ADAM beamline [20,21]of the Institut Laue-Langevin(ILL),Grenoble, France,using a monochromatic cold neutron beam.In Fig.2(b)we have shown spin-polarized neutron reﬂectiv-ity data taken at2K by applying a magneticﬁeld of13 kOe along an in-plane direction(refer Fig.1).It is known that,if the polarization of the neutrons deﬁned to be par-allel(+)or antiparallel(-)to the appliedﬁeld direction (along+y axis)[13,14,22],the intensity of a multilayer Bragg peak in this geometry increases with eﬀective scat-tering length b eﬀ=b±Aµy with A=0.2695×10−4˚A/µB.In the left inset of Fig.2(b)we have shown inten-sity proﬁles of parallel(+)and anti parallel(-)incident neutrons at theﬁrst peak position.The average of(+) and(-)proﬁles represent the non-magnetic contribution to the reﬂectivity.Systematic analysis of all these pro-ﬁles provide us the value ofµy,the component of aver-age moment per gadolinium ion along+y direction.The obtained values ofµy as a function of H at4.2K and at1.75K using the CRISP and ADAM spectrometers respectively are shown in Fig.2(a)along with data ob-tained from the magnetization measurements[17]at2K and5K.Results of these two independent measurements show that the obtained average saturated moment per gadolinium ion is much less than the expected7µB and conﬁrms the existence of a heterogeneous phase.In the right inset of Fig.2(b)we have shown the transverse dif-fuse neutron scattering intensity proﬁle at theﬁrst Bragg peak.The hyper-geometric line shape proﬁle conﬁrms that the in-plane correlation is logarithmic in nature and that the interfaces are conformal[23,24].It should be noted that unlike in x-ray measurements the scattering here originates primarily from the metal heads.The line shape and the associated parameters were found to be independent of T,H and hence exhibit the absence of conformality in the magnetic correlations between inter-faces.This again conﬁrms that the LBﬁlms represent a collection of isolated2D spin-membranes of gadolinium ions.Now we present the results of conventional magneti-zation measurements carried out at sub-Kelvin temper-ature to understand the nature of the ordering.These measurements were performed in a conventional way by measuring forces exerted on a sample situated in a spa-tially varying magneticﬁeld with a Faraday balance[25]. In Fig.2(a)we have shown M vs.H data taken at100mK and500mK temperature in an in-plane(+y)direction. This data reconﬁrms the absence of hysteresis and re-manence(M=0at H=0).The saturation value of the net magnetization at100mK and500mK found to be 12.7×10−6emu/mm2∼=5.4µB/Gd atom;much lower than the expected7.0µB/Gd atom for a homogeneous ferromagnetic phase.In Fig.3(a)we have shown the magnetization data taken with diﬀerentﬁelds as a function of tempera-ture.At higher temperatures these data wereﬁtted with Eq.(5),and the expected exponential dependence is also observed in the magnetization data extracted from our neutron reﬂectivity measurements(inset of Fig.3(a)). The values ofγobtained fromﬁtting were found to in-crease with the reduction of H and at0.25kOe it is found to be2.162K−1.It is also observed that at a lowerﬁeld, the magnetization at aﬁxed temperature is nearly pro-portional to the appliedﬁeld(5.03×10−7at0.25kOe3and1.29×10−6emu/mm2at0.5kOe and at a tem-perature0.9K)as predicted for inhomogeneous striped phases(refer Eq.(5)).The amount of majority phase grows exponentially as we lower the temperature for each appliedﬁeld but below a certain temperature this growth stops as the walls of the majority phase freeze.Below this temperature measured data do not follow Eq.(5) and the net magnetization of the majority phase M(T) increases with lowering temperature following the ther-mally activated spin waves as given in Eq.(4).Weﬁt-ted all the data with Eq.(4)and obtained M0values as0.9×10−6,1.6×10−6,3.2×10−6,4.5×10−6,7.9×10−6,9.5×10−6emu/mm2with0.15,0.25,0.5,1.0,2.5, 5.0kOe magneticﬁelds respectively.These saturation values of net magnetization indicate that the percent-age of the ferromagnetic phase is increasing from7.1% to74.8%as we approach the maximum saturation value of net magnetization obtained of12.7×10−6emu/mm2 (∼=5.4µB/Gd atom)as shown in Fig.2(a).We extracted the value of exchange J as8.76×10−19erg(or H ex= 0.165kOe)from theﬁtted value of A(=1.02K−1)for the0.25kOe data.We obtainedβas3.4for all the data and hence|K eﬀ|was calculated to be1.7×10−19erg (or H eﬀk=0.19kOe)for0.25kOe data giving T c=26 mK.In this calculation g was6.88×10−18erg,assum-ing that one gadolinium atom occupies2.5˚A×20˚A2,as obtained from neutron and x-ray analysis(refer Fig.1). This proves that we are dealing with an inhomogeneous phase as0<|K eﬀ|<K c(=8.89×10−17erg).Al-though Eq.(4)describes the temperature dependence of the magnetization for ferromagnetic ordering of both in-plane and out-of-plane spins,the argument of the loga-rithmic function can become less than1only for in-plane ordering.Unusually low values of H ex and H eﬀk with a rather large value of H d(=16.3kOe)makeβT<1even for T>T c–this situation has not been reported ear-lier to the best of our knowledge.It is interesting to note that all the magnetization data shown in Fig.3(a) attains respected saturation values M0at temperature T0=1/β(≃0.29K)and a maximum magnetization at temperature T m=1/(eβ)(≃0.108K).Our experimen-tal uncertainties below100mK prohibit us from com-menting on any reduction of magnetization below this T m but Eq.(4)withβT<1,all the data isﬁtted quite well. Further theoretical development is required to under-stand the thermal activation of spin-waves with in-plane ordering especially as we approach below T c(=26mK). In Fig.3(b)we have shown zero-ﬁeld-cooled(ZFC)and ﬁeld-cooled(FC)magnetization data taken with0.15kOe and0.5kOeﬁeld along with theﬁtted curve from Eq.(4). We observe a blocking temperature(T b)of125mK be-low which there is branching in both the ZFC and FC data.This result reconﬁrms that the observed ferromag-netic ordering requires an externalﬁeld to stabilize and such a low T b indicates the existence of very small spin clusters in the ZFC phase.Application of theﬁeld lowers the activation energy required for the randomly oriented domains to increase the number of spins in the ferro-magnetically ordered majority phase and increases the activation energy of the reverse transition[6].As a re-sult we do not observe T b in the measured temperature range for0.5kOe.In conclusion,we have demonstrated that polarized neutron scattering and conventional magnetization mea-surements can be used to study2D ferromagnetic order-ing of in-plane spins using a stack of magnetically uncor-related spin-membranes formed with gadolinium stearate LBﬁlm.The in-plane ordering observed here shows that a spontaneous magnetization is absent even at100mK and saturation value of the net magnetization increases with a lowering in temperature.The magnetization is found to increase exponentially with a lowering in tem-perature due to the exponential increase of the physical extent of the ferromagnetic domains in the heterogeneous phase.The ferromagnetic domains ultimately saturate following T ln(βT):characteristic of thermally activated spin-waves and are found to be valid for evenβT≤1. We believe these experimental results will initiate further theoretical development.[1]A.Aharoni,Introduction to the theory of Ferromagnetism(Oxford University Press)2000.[2]C.M.Schneider,and J.Kirschner,Handbook of surfacescience(eds.K.Horn,and M.Scheﬄer),511,(Elsevier, Amsterdam,2000).[3]N.D.Mermin and H.Wagner,Phys.Rev.Lett.17,1133(1966);17,1307(1966).[4]P.Bruno,Phys.Rev.Lett.87,137203(2001).[5]H.J.Elmers,G.Liu,and U.Gradmann,Phys.Rev.Lett.63,566(1989);H.J.Elmers,Intern.J.Mod.Phys.B9, 3115(1995).[6]K.De’Bell,A.B.Maclsaac,J.P.Whitehead,Rev.Mod.Phys.72,225(2000).[7]P.Bruno,Phys.Rev.B43,6015(1991).[8]A.Kashuba,and V.L.Pokrovsky,Phys.Rev.Lett.70,3155(1993).[9]P.Gambardella,A.Dallmeyer,K.Maiti,M.C.Malagoli,W.Eberhardt,K.Kern,and C.Carbone,Nature(Lon-don)416,301(2002).[10]A.B.MacIsaac,J.P.Whitehead,M.C.Robinson,andK.De’Bell,Phys.Rev.B51,16033-16045(1995).[11]S.V.Male’eV,Sov.Phys.JETP bf43,1240(1976).[12]P.Bruno,Mat.Res.Soc.Sym.Proc.231,299(1992).[13]C.G.Shull,and J.S.Smart,Phys.Rev.76,1256(1949).[14]G.P.Felcher,Phys.Rev.B24,R1595(1981).[15]M.K.Sanyal,M.K.Mukhopadhyay,M.Mukherjee,A.Datta,J.K.Basu,and J.Penfold,Phys.Rev.B65, 033409(2002).[16]J.K.Basu,and M.K.Sanyal,Phys.Rep.363,1(2002).[17]M.K.Mukhopadhyay,M.K.Sanyal,M.D.Mukadam,S.M.Yusuf,and J.K.Basu,Phys.Rev.B68,174427 (2003).[18]J.Penfold,and R.K.Thomas,J.Phys.:Condens.matter4Figure captions:FIG.1:(a)Schematic diagram of the out-of-plane and in-plane structure of the gadolinium stearate Langmuir Blodgett ﬁlm is shown with the scattering geometry employed for the polarized neutron reﬂectivity measurements.x−z plane is the scattering plane and the magneticﬁeld is applied along the+y direction.λandαare the wavelength of the radiation and angle of incidence respectively.FIG.2:(a)In-plane Magnetization curves obtained as a func-tion of theﬁeld(H)using neutron reﬂectivity measured at 4.2K(diamond)and1.75K(star)compared with conventional magnetization data[17]measured at2K(down-triangle)and 5K(up-triangle).Solid lines are theﬁts with a modiﬁed Bril-louin function[17].Magnetization measured at100mK and 500mK is shown for the1st(symbols)and2nd(line)cycle of the hysteresis loop.(b)Neutron reﬂectivity data(sym-bols)at H=13kOe and at T=2K for the neutron spin along(+)and opposite(-)to the magneticﬁeld direction with the correspondingﬁt(line).In the left inset theﬁrst Bragg peak is shown in(+)and(-)channels in an expanded scale.Right inset:Transverse diﬀuse neutron scattering pro-ﬁles(symbols)measured at2K with unpolarized and polar-ized neutron beams.The solid line is aﬁtted hypergeometric curve as described in the text.FIG.3:(a)Sub-Kelvin magnetization results with various appliedﬁelds(symbols)ﬁtted with Eq.(4)(Black line)and with Eq.(5)(wine coloured dashed lines).Dotted lines indi-cate the temperatures T m and T0(refer to text).Inset shows the magnetization obtained from neutron measurements as a function of temperature(symbols)andﬁt with Eq.(5)(line).(b)ZFC(green circles)and FC(blue stars)along with theﬁt (line)for FC measurements.2,1369(1990).[19]J.P.Goﬀ,P.P.Deen,R.C.C.Ward,M.R.Wells,S.Langridge,R.Dalgleish,S.Foster,S.Gordeev,J.Mag.Mag.Mat.240,592(2002).[20]H.Zabel,Physica B198,156(1994).[21]V.Leiner,K.Westerholt, A.M.Blixt,H.Zabel, B.Hj¨o rvarsson,Phys.Rev.Lett.91,037202(2003). [22]H.Kepa,J.Kutner-Pielaszek,A.Twardowski,C.F.Ma-jkrzak,J.Sadowski,T.Story,and T.M.Giebultowicz, Phys.Rev.B64,121302(2001).[23]M.K.Sanyal,S.K.Sinha,K.G.Huang,and B.M.Ocko,Phys.Rev.Lett.66,628(1991);J.K.Basu,S.Hazra, and M.K.Sanyal,Phys.Rev.Lett.82,4675(1999). [24]The measured roughness and‘true’roughness[23]of theinterfaces are calculated to be2.3˚A and5.4˚A respec-tively and we get an eﬀective surface tension equal to10 mN/m.[25]T.Sakakibara,H.Mitamura,T.Tayama,H.Amitsuka,Jpn.J.Appl.Phys.33,5067(1994).xyzOut-of-plane direction In-plane directionq zH49Å5Å(b)ααq z ()αλπsin 4=20 Å210203040024********X 1065 K2 K4.2 K1.75 K500 mK 100 mKM a g n e t i z a t i o n ( e m u / m m 2)Field ( kOe )0.10.20.30.410-510-410-310-210-1+ spin - spinR e f l e c t i v i t yq z ( Å -1)0.1200.1250.1300.1350.0020.004q z (Å-1)R e f l e c t i v i t y10-410-310-210-1100H = 0 kOe H = 20 kOeH = 2 kOe +spin H = 2 kOe - spinN o r m a l i z e d c o u n tq x ( Å -1)(a)(b)(b)(a)0.00.10.20.30.40.50.601234H=150 OeH=500 OeX 106Field CooledZero Field CooledM a g n e t i z a t i o n ( e m u / m m 2)Temperature ( K )0.00.30.60.9 1.2 1.5024681012T mT 05.0 kOe2.5 kOe1.0 kOe 0.5 kOe 0.25 kOex 106M a g n e t i z a t i o n ( e m u / m m 2)Temperature ( K )510152025300369x 106Temperature ( K )M a g n e t i z a t i o n( e m u / m m 2)。

翻译

Unit 12. 出席晚宴的客人对那个美国人威严的语气感到有点意外。

The guests at the dinner party were slightly surprised at the commanding tone of the American.4. 当全部乘客都向出口处(exit) 走去时，他却独自留在座位上，好像不愿意离开这架飞机似的。

While all the other passengers made for the exit, he alone remained in his seat as if unwilling to leave the plane.6. 南希虽然很想参加辩论，但腼腆得不敢开口。

While she felt like joining in the argument, Nancy was too shy to open her mouth.8. 猎人一看见有只狐狸从树丛中出现并向他设下(lay) 的陷阱(trap) 方向跑去，脸上顿时闪出了兴奋的表情。

The hunter’s face lit up with excitement as soon as he saw a fox emerge from among the bushes and run in the direction of / make for the trap he had laid.Unit 22) 这些青年科学家通过现场观察，获得了研究工作所需的第一手资料。

By making on-the-spot observations, the young scientists obtained first-hand information they needed in their research work.4) 委员会成员在新机场最佳选址(location) 这一问题上持有不同意见。

The committee members have conflicting opinions as to the best location of the new airport.6) 我们产品质量的稳步提高在很大程度上是由于设备有所改进。

气泡形核 bubble nucleation ,growth and coalescence

Bubble nucleation,growth and coalescence during the 1997Vulcanian explosions of Soufrière Hills Volcano,MontserratT.Giachetti a ,b ,c ,⁎,T.H.Druitt a ,b ,c ,A.Burgisser d ,L.Arbaret d ,C.Galven eaClermont Université,UniversitéBlaise Pascal,Laboratoire Magmas et Volcans,BP 10448,F-63000Clermont-Ferrand,France bCNRS,UMR 6524,LMV,F-63038Clermont-Ferrand,France cIRD,R 163,LMV,F-63038Clermont-Ferrand,France dInstitut des Sciences de la Terre d'Orléans,Universitéd'Orléans,1A,rue de la Férollerie,45071Orléans Cedex 2,France eLaboratoire des Oxydes et Fluorures,Facultédes Sciences et Techniques,Universitédu Maine,Avenue Olivier Messiaen,72085Le Mans Cedex 9,Francea b s t r a c ta r t i c l e i n f o Article history:Received 29July 2009Accepted 5April 2010Available online 13April 2010Keywords:Vulcanian explosions Soufrière Hills vesiculationbubble nucleation bubble growth coalescenceamphibole boudinageSoufrière Hills Volcano had two periods of repetitive Vulcanian activity in 1997.Each explosion discharged the contents of the upper 0.5–2km of the conduit as pyroclastic ﬂows and fallout:frothy pumices from a deep,gas-rich zone,lava and breadcrust bombs from a degassed lava plug,and dense pumices from a transition zone.Vesicles constitute 1–66vol.%of breadcrust bombs and 24–79%of pumices,all those larger than a few tens of µm being interconnected.Small vesicles (b few tens of µm)in all pyroclasts are interpreted as having formed syn-explosively,as shown by their presence in breadcrust bombs formed from originally non-vesicular magma.Most large vesicles (N few hundreds of µm)in pumices are interpreted as pre-dating explosion,implying pre-explosive conduit porosities up to 55%.About a sixth of large vesicles in pumices,and all those in breadcrust bombs,are angular voids formed by syn-explosive fracturing of amphibole phenocrysts.An intermediate-sized vesicle population formed by coalescence of the small syn-explosive bubbles.Bubble nucleation took place heterogeneously on titanomagnetite,number densities of which greatly exceed those of vesicles,and growth took place mainly by decompression.Development of pyroclast vesicle textures was controlled by the time interval between the onset of explosion –decompression and surface quench in contact with va-plug fragments entered the air quickly after fragmentation (∼10s),so the interiors continued to vesiculate once the rinds had quenched,forming breadcrust bombs.Deeper,gas-rich magma took longer (∼50s)to reach the surface,and vesiculation of resulting pumice clasts was essentially complete prior to surface quench.This accounts for the absence of breadcrusting on pumice clasts,and for the textural similarity between pyroclastic ﬂow and fallout pumices,despite different thermal histories after leaving the vent.It also allowed syn-explosive coalescence to proceed further in the pumices than in the breadcrust bombs.Uniaxial boudinage of amphibole phenocrysts in pumices implies signi ﬁcant syn-explosive vesiculation even prior to magma fragmentation,probably in a zone of steep pressure gradient beneath the descending fragmentation front.Syn-explosive decompression rates estimated from vesicle number densities (N 0.3–6.5MPa s −1)are consistent with those predicted by previously published numerical models.©2010Elsevier B.V.All rights reserved.1.IntroductionExplosive volcanic eruptions are driven by the nucleation,growth and coalescence of gas bubbles,followed by fragmentation of the magmatic foam into a suspension of pyroclasts and gas that is discharged at high velocities into the atmosphere.Studies of pyroclast textures,coupled with experimental and numerical approaches,have advanced understanding of these processes (Lensky et al.2004;Spieler et al.2004b;Adams et al.2006;Toramaru 2006;Gardner 2007;Cluzel et al.2008;Koyaguchi et al.2008and references therein),but many questions remain.One concerns the relative importance of homogeneous versus heterogeneous nucleation.Homogeneous nu-cleation requires gas supersaturations of at least several tens of MPa (Mangan and Sisson 2000;Mourtada-Bonnefoi and Laporte 2002;2004;Mangan et al.2004),whereas heterogeneous nucleation requires lower supersaturations (Hurwitz and Navon 1994;Gardner 2007;Cluzel et al.,2008).The degree of equilibrium between gas and melt during bubble growth also has an effect.Equilibrium degassing requires ef ﬁcient volatile diffusion coupled with melt viscosity low enough to allow free gas expansion (Lyakhovsky et al.,1996;Liu and Zhang,2000;Lensky et al.,2004).High degrees of disequilibrium favour short-lived eruptions,whereas equilibrium allows more sustained fragmentation (Melnik and Sparks,2002;Mason et al.,2006).Another issue concerns the timing of bubble growth andJournal of Volcanology and Geothermal Research 193(2010)215–231⁎Corresponding author.Clermont Université,UniversitéBlaise Pascal,Laboratoire Magmas et Volcans,BP 10448,F-63000Clermont-Ferrand,France.E-mail address:giachettithomas@club-internet.fr (T.Giachetti).0377-0273/$–see front matter ©2010Elsevier B.V.All rights reserved.doi:10.1016/j.jvolgeores.2010.04.001Contents lists available at ScienceDirectJournal of Volcanology and Geothermal Researchj o u r n a l h o me p a g e :w w w.e l s ev i e r.c o m/l o c a t e /j vo l g e o r e scoalescence relative to fragmentation and eruption.Some authors postulate little growth following fragmentation(Klug and Cashman, 1991)whereas others envisage signiﬁcant post-fragmentation growth(Thomas et al.1994;Kaminski and Jaupart,1997).Post-fragmentation bubble growth is largely controlled by melt viscosity, being important in maﬁc melts and less so in silicic melts with viscosities N108–109Pa s(Thomas et al.,1994;Gardner et al.,1996; Kaminski and Jaupart,1997).Bubble coalescence and connections control permeability acquisition and the ability of magma to outgas during ascent.Vesicle size distributions provide information on magma vesicu-lation history.Pumices commonly contain multiple vesicle popula-tions covering a large range of sizes(Klug and Cashman,1996;Klug et al.,2002;Adams et al.,2006)that may result from coalescence following a single nucleation event(Orsi et al.,1992;Klug and Cashman,1994,1996;Klug et al.,2002;Burgisser and Gardner,2005). Alternatively,each population may represent a distinct nucleation event,consistent with some ascent models which predict multiple events for viscous magma(Witham and Sparks,1986;Proussevitch and Sahagian,1996;Blower et al.,2001;Massol and Koyaguchi,2005). Small vesicles are commonly attributed to syn-explosive vesiculation that generates an exponential size distribution(Mangan et al.,1993; Klug and Cashman,1996;Klug et al.,2002;Adams et al.,2006).Size distributions of larger populations typically obey power laws usually attributed to coalescence(Klug et al.,2002;Houghton et al.,2003; Gurioli et al.,2005;Adams et al.,2006;Klug and Cashman,1996), although multiple nucleation events also generate power-law distributions(Blower et al.,2001).Magma decompression rates can be estimated from vesicle number densities assuming a unique and brief nucleation event(Toramaru,2006;Cluzel et al.,2008).Detailed studies of eruptive products are required to address these questions and provide ground truth for models.Most vesiculation studies to date have concerned Plinian eruptions.In this paper we study vesiculation during a sequence of well documented Vulcanian explo-sions at Soufrière Hills Volcano in1997.The explosions have been previously described(Druitt et al.,2002;Cole et al.,2002)and modelled (Melnik and Sparks,2002,Clarke et al.,2002;Formenti et al.,2003;Diller et al.,2006;Mason et al.,2006),and their products studied texturally (Formenti and Druitt,2003;Clarke et al.,2007)and chemically(Harford et al.,2003).A key feature was the eruption of pyroclasts of a wide range of types,including dense lava fragments,breadcrust bombs and pumices of different densities.Textural analysis,including a set of high-resolution vesicle-size distributions,enables us to recognize populations of vesicles formed by explosion decompression,quantify bubble nucleation mechanisms and decompression rates,and constrain the timing of bubble nucleation,growth and coalescence during,and immediately following,a typical explosion.In a companion paper we present measurements of groundmass water contents and reconstruct the state of the pre-explosion conduit(Burgisser et al.,in press).2.The1997Vulcanian explosions of the Soufrière Hills VolcanoThe eruption of Soufrière Hills Volcano(Fig.1)began phreatically in July1995;extrusion of lava began in November of the same year and continued intermittently until the time of writing.The explosions in 1997occurred every3–63h(mean of∼10h)in two periods:thirteen between4and12August,and seventyﬁve between22September and 21October(Druitt et al.,2002).Each consisted of an initial high-intensity phase lasting a few tens of seconds,followed by a waning phase lasting1–3h.Multiple jets were ejected at40–140m s−1during theﬁrst10–20s of each explosion,then collapsed back to form pumiceous pyroclasticﬂows that travelled up to6km from the crater (Formenti et al.,2003).Fallout of pumice and ash occurred from high (3–15km)buoyant plumes that developed above the collapsing fountains.Fallout andﬂow took place at the same time from individual explosions.Each explosion discharged on average8×108kg of magma,about two-thirds as pyroclasticﬂows and one-third as fallout, representing a conduit drawdown of0.5–2km(Druitt et al.,2002). Studies of quench pressures using microlite contents and glass water contents support a maximum drawdown of∼2km(Clarke et al.,2007; Burgisser et al.,in press).Each explosion started when magma overpressure exceeded the strength of an overlying degassed plug and a fragmentation front propagated down the conduit at a few tens of m s−1 (Druitt et al.,2002;Clarke et al.,2002;Melnik and Sparks,2002;Spieler et al.,2004a;Diller et al.,2006;Mason et al.,2006).After each explosion, magma rose up the conduit before the onset of a new explosion.The Soufrière Hills andesite contains phenocrysts of plagioclase, hornblende,orthopyroxene,magnetite,ilmenite and quartz set in rhyolitic glass.The pre-eruptive temperature was∼850°C(Devine et al., 2003).3.MethodolgyField work was carried out in2006and2008at three sites(Fig.1): sites1and2are situated on the fans of overlapping pyroclasticﬂow lobes from the explosions,and site3is a composite layer of fallout pumice from many explosions.Fallout pumices were also collected at a fourth site(site4;Fig.1)during an explosion in August1997.Field descriptions were made using a rock saw to cut perpendicular to any ﬂow banding and parallel to any crystal fabric,and over100 representative pyroclasts were taken for laboratory study.Abundances of isolated and connected vesicles were measured on 2–5cm cubes cut from30breadcrust bombs and34ﬂow and fall pumices using a Multivolume1305Helium Pycnometer and the method of Formenti and Druitt(2003),which is explained in the Supplementary electronic material.Separate measurements were made on the rims and cores of22 breadcrust bombs.Twenty-six of the pumice clasts ranged from lapilli to block size,all being b20cm in diameter.Measurements were also made on multiple core-to-rim samples from eight pumices N30cm in diameter. Texturally or compositionally banded pyroclasts were not included.Microscopic observations were made on the broken surfaces of pyroclast fragments using a Jeol JSM-591LV Scanning Electron Micro-scope(SEM)at an acceleration of15kV,and on polished epoxy-impregnated thin sections using the SEM and a stereomicroscope.Six samples representative(in terms of vesicularity and texture)of the pyroclast assemblage were chosen for high-resolution analysis of vesicle and crystal size distributions.Banded clasts,and those with a signiﬁcant fraction of non-spherical vesicles,were excluded,thereby justifying use of a single,randomly oriented thin section for each sample.Vesicle and crystal size distributions were measured by image analysis in two dimensions(Toramaru,1990;Mangan et al.,1993; Klug and Cashman1994,1996;Klug et al.,2002;Adams et al.,2006;Shea et al.,2010).The technique,described fully in Appendix A,allowed objects as small as∼1µm to be measured.Differential epoxy penetration enabled us to distinguish interconnected from isolated vesicles.To represent the state of the magma immediately prior to the last discernible stage of coalescence,we manually‘decoalesced’neighbouring vesicles separated by a partially retracted wall.Volume distributions were assumed to equal area distributions(Klug et al.,2002).Volumetric number densities(N v)were calculated from area number densities(N a) using both the methods of Cheng and Lemlich(1983)and of Sahagian and Proussevitch(1998),which yield very similar values(Table1).Values of N v presented in this paper are those obtained using theﬁrst method,for reasons discussed in the Appendix A.4.Field descriptionsThe pyroclast assemblage consists predominantly of pumices of different colours,vesicularities and textures,with less than a few percent of breadcrust bombs and dense glassy lava clasts.Pyroclasts of all types were present in the pyroclasticﬂow deposits,although the216T.Giachetti et al./Journal of Volcanology and Geothermal Research193(2010)215–231relative proportions varied from lobe to lobe,while dense lava and breadcrust bombs were absent in the fallout.The samples described below come from several different explosions,and cannot be assigned to speci ﬁc dates/times owing to the complex superposition of ﬂow and fallout lobes from the many events.They represent the products of an ‘average ’explosion,as justi ﬁed by (1)the ﬁrst-order similarity of all the explosions (Druitt et al.,2002),and (2)the presence of the entire pyroclast spectrum in all pyroclastic ﬂow lobes we examined.Pumices in the pyroclastic-ﬂow deposits occur as lapilli and blocks up to N 1m in diameter with subangular-to-rounded shapes due to abrasion during transport.They range from beige,well vesiculated varieties,to grey,brown or black denser varieties (Fig.2a –b).A pink colouration affects the surfaces of many blocks,but rarely pervades the interiors.While the majority of pumices are texturally homoge-neous in hand specimen,some denser ones are ﬂow banded with phenocryst alignment in the plane of banding.Rare compositional banding de ﬁned by trails of disintegrated ma ﬁc inclusions also occurs.All pumice clasts (as distinguished from breadcrust bombs)lack surface breadcrusting.This probably cannot be explained by abrasion,because breadcrust fragments are not observed in the ﬂow matrices.All pumices smaller than ∼30cm lack radial gradients in vesicle abundance or size.However,some blocks larger than this exhibit visibly obvious radial gradients in vesicle size,with an outer 3–7-cm-thick rind with vesicles up to several mm,and a more coarsely vesicular interior containing vesicles up to an order of magnitude larger (Fig.2c).In some cases a crude cm-scale radial jointing affects the rind.The rind is inferred to represent the initial textural state of the pumice,while the interior records vesicle coarsening that took place during or after emplacement.The possibility that the interior represents the initial state,and that the rind developed by compaction during rolling in the pyroclastic ﬂow,is not favoured because (1)the rinds texturally resemble the majority of smaller pumice blocks and lapilli,whereas vesicles in the interiors are abnormally coarse,and (2)no circumferential ﬂattening of rind vesicles is observed.Many blocks also contain large voids up to several cm across,including anastamosing vesicle pipes and channels,ductile tears in the plane of ﬂow banding,and curviplanar tears and cracks subparallel to clast margins (Fig.2d),which together account for b 10%of the total vesicularity.Fallout pumices are up to several cm in size and most preserve their original eruption –fragmentation shapes,unmodi ﬁed by abrasion in pyroclastic ﬂows or breakage on ground impact.They range in colour from white to brown and in shape from spheroidal to tabular,the latter comprising about three-quarters of the sample suite.Again,no surface breadcrusting is observed.Breadcrust bombs occur from a few cm to over a metre in diameter.They have vesicular interiors surrounded by darker,less vesicular b 10mm glassy rinds.A continuous range of textural varieties are observed between two endmembers.Coarsely breadcrusted bombs are relatively dense,with well de ﬁned,dark-grey-to-black,poorly-to-non-vesicular rinds,broad,deep surface fractures de ﬁning large polygons,and grey-to-brown vesicular interiors (Fig.2e –f).Finely breadcrusted bombs are less dense,with diffuse,pale vesicular rinds,ﬁner polygonal networks of narrower,shallower surface fractures,and paler,commonly ﬂow-banded interiors (Fig.2g –h).Some bombs that broke during eruption exhibit two generations of breadcrusting,the breakage surface being more ﬁnely breadcrusted than the original,outer surface of the bomb.Breakage is inferred to have exposed the already vesicular interior,which then developed a second generation of ﬁner breadcrust-ing.Bombs were abraded during transport in the pyroclastic ﬂows;most lack completely preserved breadcrust surfaces with sharp edges and corners,and partial rind removal,rounding of polygon edges,and abrasion of vesicular interiors are common.Clasts of black,essentially nonvesicular lava resembling the glassy rinds of the coarsely breadcrust bombs are interpreted as an integral component of the explosion-pyroclast suite.On the other hand,grey-to-brown holocrystalline lava and cinderblock clasts resembling typical dome rock are probably derived either from the crater walls or from earlier block-and-ash ﬂow deposits traversed by the explosion pyroclastic ﬂows.Fig.1.Map of Montserrat showing Soufrière Hills Volcano and sampling locations.Grey:pyroclastic ﬂow deposits of the 1997Vulcanian explosions.217T.Giachetti et al./Journal of Volcanology and Geothermal Research 193(2010)215–231Fig.2.Pumices and breadcrust bombs from the explosions.a)Dark brown pumice with 60%vesicularity,b)Pale pumice with 76%vesicularity,c)Large grey pumice exhibiting a radial gradient in vesicularity,line marks the outer surface of the clast,d)Curviplanar tears and cracks subparallel to clast margins in a dense pumice,e –f)Exterior and cross section of a coarsely breadcrust-bomb,g –h)Exterior and cross section of a ﬁnely breadcrusted bomb.219T.Giachetti et al./Journal of Volcanology and Geothermal Research 193(2010)215–2315.Pyroclast vesicularitiesVesicularities of texturally homogenous pumice lapilli and blocks range from24to79vol.%(Fig.3)and correlate with colour,being lowest in darker pumices and higher in paler ones.The fraction of isolated vesicles(isolated divided by total vesicularity)is universally low(b0.25,with85%b0.1).Flow pumices cover the entire vesicularity range and have isolated fractions of0–0.13,whereas fallout pumices have vesicularities of43–72vol.%and isolated fractions of0.04–0.14,a single sample having0.25(Fig.3).No variation of either vesicularity or isolated vesicle fraction with clast size is observed.Vesicularity proﬁles across eight N30cm pumice blocks are shown in Fig.4.Four of these appeared homogeneous in theﬁeld,and four had visually obvious radial gradients in vesicle size.The four homogeneous blocks(SHV4–12–13–22)lack signiﬁcant gradients in vesicularity from core to rim,as anticipated from inspection.The four vesicle-size-graded blocks(SHV2–14–23–25),on the other hand, exhibit vesicularity gradients,but these vary from sample to sample and no systematic decrease in vesicularity from core to rim is evident.The coarse interiors of these pumices are no more vesicular than the moreﬁnely vesicular rims.Textural coarsening in the interiors therefore took place without inﬂation,as consistent with the absence of surface breadcrusting.Breadcrust-bombs differ from pumices in that(1)their vesicular-ity range(20–66vol.%most lying between35and55%,Fig.3)is smaller,and highly vesicular(N66%)samples are not observed;and (2)the fraction of isolated pores(0.05–0.33,N80%being0.1–0.2) is higher than in pumices of similar vesicularity.Bomb rinds contain 1–25vol.%vesicles,most of which are isolated.Rind and interior vesicularities are broadly correlated(Fig.5).Coarsely breadcrusted bombs have the lowest vesicularities,both in rinds and interiors,and ﬁnely breadcrusted bombs are more vesicular.It is the existence of vesicular rinds onﬁnely breadcrusted bombs that gives these bombs their pale colours and make distinction between rind and interior less clear than in the coarsely breadcrusted bombs.Full tables of vesicularity data are provided as Supplementary electronic material.6.Microscopic vesicle texturesThe pyroclasts contain vesicles with a broad range of sizes set in microlite-bearing groundmass.In this section we focus on vesicles less than a few mm in diameter present in hand specimens,and distinguish three populations:small(less than a few tens ofµm),intermediate(few tens to a few hundreds ofµm)and large(few hundreds ofµm to a few mm).It is shown later that these three populations also have genetic signiﬁcance.Vesicle textures in fallout andﬂow pumices are very similar and are described together.The large vesicles form interconnected networks with curved,scalloped walls indicative of rge vesicles in the more vesicular pumices are quasi-spherical to elliptical in shape. Those in dense pumices commonly have more ragged,ﬁssure-like shapes,suggesting that perhaps they already existed prior to explosion. About15%of the large vesicles are angular voids associated with fractured amphibole phenocrysts(Fig.6a).Intermediate-sized vesicles in all pumices have variably rounded to ragged shapes and,like the large ones,form interconnected networks in three dimensions.In contrast, small vesicles are commonly spherical and many are isolated;they either form a‘matrix’in which the intermediate vesicles are dispersed (Fig.6b),or are situated in the walls separating the latter.In some samples the smallest isolated vesicles form sub-spherical clusters several tens of microns in diameter that protrude with bulbous, cauliform shapes into larger vesicles(Fig.6c;Formenti and Druitt, 2003).There is textural evidence that many vesicles of intermediate size formed by coalescence of the small vesicles(rather than pre-existing them),the process commonly being preserved quenched in progress (Fig.6d).The sizes of some intermediate vesicles appear to be inherited from the clusters of small vesicles when the latter coalesced while preserving the overall sub-spherical form of the cluster.Vesicles in pumices are commonly observed in spatial association with rge,angular voids are associated with fractured amphiboles,and have two endmember types:(1)voids in amphiboles boudinaged uniaxially in the plane ofﬂow foliation,with well deﬁned length-perpendicular fractures(Fig.7);(2)voids in amphiboles that are fractured both perpendicular and parallel to length,and the fragments dispersed around the vesicle margins in a manner suggestive of more isotropic expansion.In both types,crystal fragments arecommonlyFig.3.Plot of connected versus total vesicularity for all the samples of this vasamples from dome collapses at Soufrière Hills Volcano are also shown(Formenti andDruitt,2003).As connected vesicularities could not be determined for breadcrustbombs rinds,we just show the range of bulk vesicularities obtained(thick blackline).Fig.4.Vesicularity as a function of relative position inside large pumices(N30cm).Filled diamonds with solid lines are those pumices that were judged in theﬁeld to betexturally homogeneous;squares with dashed lines are those that had larger vesicles inthe interior than in therind.Fig.5.Relationships between rind and interior vesicularities of breadcrust bombs,including both coarsely andﬁnely breadcrusted types.220T.Giachetti et al./Journal of Volcanology and Geothermal Research193(2010)215–231connected by thin,delicate threads of glass generated either by the bursting of melt inclusions,or by the pulling-out of thin,pre-existing melt ﬁlms in incipient cracks.A single type of amphibole-associated void is commonly dominant within a given pumice block.Type 1is observed in ∼45%of pumices and type 2in ∼35%,the remaining ∼20%of pumices lacking voids associated with amphibole.Another common texture involves radial arrangements of stretched vesicles around phenocrysts of plagioclase or amphibole (Fig.6e).This is attributed to expansion of a magmatic foam around a rigid crystal;it cannot be due to heterogeneous bubble nucleation because in each case the vesicles are separated from the crystal by a thin glass ﬁlm,showing that the crystal was not wetted by gas.Only in the case of titanomagnetite is it common to see vesicles in direct contact with crystals without intervening glass,suggesting that titanomagnetite provided nucleation sites for bubbles (Fig.8).There is abundant evidence that bubble coalescence was ongoing at all scales larger than a few µm at the time of sample quench:ovoid,neck-like connections with partially retracted walls between neighbouring vesicles (Fig.6d),wrinkling of thin vesicle walls (Fig.6f),the occurrence of thin glass ﬁbres,and the interconnection of all but a fraction of the smallest vesicles.Minimum observed vesicle wall thicknesses are b 1µm.Breadcrust bomb rinds contain small,mostly isolated,vesicles that are irregularly distributed,being most abundant near rind-penetratingsurface fractures and around phenocrysts (Fig.9a,c).Areas of vesicle-free groundmass occur in the rinds of coarsely breadcrusted bombs,but not in those of the ﬁnely breadcrusted bombs.The lower limit of the rind is commonly marked by string-like networks of small vesicles,which then merge to form the more uniformly distributed vesicle population of the interior.The interiors of all bombs contain distinct large and small vesicle rge vesicles are invariably associated with fractured amphiboles,like those in the pumices.However,well developed uniaxial boudinage is never observed in breadcrust bombs,and the voids are mostly of the more isotropic type 2.Small vesicles are uniformly distributed throughout the bomb interiors (Fig.9b,d);they are mostly isolated,with quasi-spherical forms,and commonly occur in strings and clusters around crystals and large vesicles.Evidence for vesicle coalescence is abundant in bomb interiors,although less so than in pumices.7.Size distributions of vesicles and crystalsThe six samples chosen for analysis of vesicle and crystal size distributions were a coarsely breadcrusted bomb (BCP1),a ﬁnely breadcrusted bomb (BCP43),three pyroclastic-ﬂow pumices (AMO29,AMO36and PV3),and a fallout pumice (R2).SeparatemeasurementsFig.6.SEM images of broken surfaces (a –d)and thin sections (e –f)of pumices.a)Angular void in a fractured amphibole phenocryst,the fragments being connected by thin glass ﬁbres (white arrows),b)Visual evidence for three different size populations (large,intermediate and small)of vesicles in pumices,c)Cauliform-shaped clusters of small vesicles protruding into intermediate ones,d)Evidence for coalescence of small vesicles to form intermediate-sized ones,e)Microphenocryst of plagioclase surrounded by radiating,elongated vesicles,f)Wrinkling of vesicle wall indicative of the onset of rupture (white arrow).221T.Giachetti et al./Journal of Volcanology and Geothermal Research 193(2010)215–231。

专题05 阅读理解D篇(2024年新课标I卷) (专家评价+三年真题+满分策略+多维变式) 原卷版

《2024年高考英语新课标卷真题深度解析与考后提升》专题05阅读理解D篇（新课标I卷）原卷版(专家评价+全文翻译+三年真题+词汇变式+满分策略+话题变式)目录一、原题呈现P2二、答案解析P3三、专家评价P3四、全文翻译P3五、词汇变式P4(一)考纲词汇词形转换P4(二)考纲词汇识词知意P4(三)高频短语积少成多P5(四)阅读理解单句填空变式P5(五)长难句分析P6六、三年真题P7(一)2023年新课标I卷阅读理解D篇P7(二)2022年新课标I卷阅读理解D篇P8(三)2021年新课标I卷阅读理解D篇P9七、满分策略（阅读理解说明文）P10八、阅读理解变式P12 变式一：生物多样性研究、发现、进展6篇P12变式二：阅读理解D篇35题变式（科普研究建议类）6篇P20一原题呈现阅读理解D篇关键词: 说明文;人与社会;社会科学研究方法研究;生物多样性; 科学探究精神;科学素养In the race to document the species on Earth before they go extinct, researchers and citizen scientists have collected billions of records. Today, most records of biodiversity are often in the form of photos, videos, and other digital records. Though they are useful for detecting shifts in the number and variety of species in an area, a new Stanford study has found that this type of record is not perfect.“With the rise of technology it is easy for people to make observation s of different species with the aid of a mobile application,” said Barnabas Daru, who is lead author of the study and assistant professor of biology in the Stanford School of Humanities and Sciences. “These observations now outnumber the primary data that comes from physical specimens(标本), and since we are increasingly using observational data to investigate how species are responding to global change, I wanted to know: Are they usable?”Using a global dataset of 1.9 billion records of plants, insects, birds, and animals, Daru and his team tested how well these data represent actual global biodiversity patterns.“We were particularly interested in exploring the aspects of sampling that tend to bias (使有偏差) data, like the greater likelihood of a citizen scientist to take a picture of a flowering plant instead of the grass right next to it,” said Daru.Their study revealed that the large number of observation-only records did not lead to better global coverage. Moreover, these data are biased and favor certain regions, time periods, and species. This makes sense because the people who get observational biodiversity data on mobile devices are often citizen scientists recording their encounters with species in areas nearby. These data are also biased toward certain species with attractive or eye-catching features.What can we do with the imperfect datasets of biodiversity?“Quite a lot,” Daru explained. “Biodiversity apps can use our study results to inform users of oversampled areas and lead them to places – and even species – that are not w ell-sampled. To improve the quality of observational data, biodiversity apps can also encourage users to have an expert confirm the identification of their uploaded image.”32. What do we know about the records of species collected now?A. They are becoming outdated.B. They are mostly in electronic form.C. They are limited in number.D. They are used for public exhibition.33. What does Daru’s study focus on?A. Threatened species.B. Physical specimens.C. Observational data.D. Mobile applications.34. What has led to the biases according to the study?A. Mistakes in data analysis.B. Poor quality of uploaded pictures.C. Improper way of sampling.D. Unreliable data collection devices.35. What is Daru’s suggestion for biodiversity apps?A. Review data from certain areas.B. Hire experts to check the records.C. Confirm the identity of the users.D. Give guidance to citizen scientists.二答案解析三专家评价考查关键能力，促进思维品质发展2024年高考英语全国卷继续加强内容和形式创新，优化试题设问角度和方式，增强试题的开放性和灵活性，引导学生进行独立思考和判断，培养逻辑思维能力、批判思维能力和创新思维能力。

Deep HST Observations of Star Clusters in NGC 1275

a rXiv:as tr o-ph/98219v12Fe b1998Deep HST Observations of Star Clusters in NGC 12751Matthew N.Carlson 2,Jon A.Holtzman 2,Alan M.Watson 3,Carl J.Grillmair 4,Jeremy R.Mould 5,Gilda E.Ballester 6,Christopher J.Burrows 7,John T.Clarke 6,David Crisp 4,Robin W.Evans 4,John S.Gallagher III 8,Richard E.Griﬃths 9,J.JeﬀHester 10,John G.Hoessel 8,Paul A.Scowen 10,Karl R.Stapelfeldt 4,John T.Trauger 4,and James A.Westphal 11ABSTRACT We present an analysis of compact star clusters in deep HST/WFPC2images of NGC 1275.B and R band photometry of roughly 3000clusters shows a bimodality in the B-R colors,suggesting that distinct old and young clusterpopulations are present.The small spread in the colors of the blue clusters isconsistent with the hypothesis that they are a single age population,with aninferred age of0.1to1Gyr.The luminosity function shows increasing numbersof blue clusters to the limit of our photometry,which reaches several magnitudespast the turnover predicted if the cluster population were identical to currentGalactic globulars seen at a younger age.The blue clusters have a spatialdistribution which is more centrally peaked than that of the red clusters.Theindividual clusters are slightly resolved,with core radii<∼0.75pc if they havemodiﬁed Hubble proﬁles.We estimate the speciﬁc frequencies of the old andyoung populations and discuss the uncertainties in these estimates.Weﬁnd thatthe speciﬁc frequency of the young population in NGC1275is currently largerthan that of the old population and will remain so as the young populationevolves,even if the majority of the low mass clusters are eventually destroyed.If the young population formed during a previous merger,this suggests thatmergers can increase the speciﬁc frequency of globulars in a galaxy.However,the presently observed young population likely contains too few clusters to havea signiﬁcant impact on the overall speciﬁc frequency as it will be observed inthe future.1.IntroductionEarly HST observations of NGC1275,the central galaxy in the Perseus cluster, revealed a population of about60blue(V-R∼0.3)star clusters surrounding the nucleus (Holtzman et al.1992).The color of these clusters suggests an age of roughly300million years based on the models of Charlot and Bruzual(1991).Spectra of the brightest object (Zepf et al.1995)also suggest an age of0.1to0.9Gyr,based on a comparison of the observed line widths to those predicted by the models of Bruzual and Charlot(1993).None of the clusters seem to have Hαemission,with the exception of one object found by Shields &Filippenko(1990),which appears to be a much younger object.The blue clusters in the original WFPC1images appear unresolved,suggesting sizes of less than15parsecs.The brightest object has V=18.9,which corresponds to M V=-15.8for H0=75km/s/Mpc and cz=5264km/s(Strauss et al.1992).The brightnesses of the blue clusters suggest masses of between2×104and1×108M⊙,depending on the assumed age and distance, if one assumes that the objects are star clusters with a Salpeter IMF.The observed sizes, luminosities,and the estimated masses suggest that these objects may be young analogues of globular clusters.In the past several years,massive young clusters have been observed in a variety of other galaxies.Lutz(1991)detected young globular cluster candidates in a ground-based study of the merger remnant NGC3597,and these have been conﬁrmed to be compact by HST observations(Holtzman et al.1996).Candidate young globular clusters have also been found in other interacting systems,including NGC7252(Whitmore et al.1993), NGC4038/9(Whitmore&Schweizer1995),NGC3921(Schweizer et al.1996),among others.A few massive clusters are seen in the starburst galaxy NGC253(Watson et al.1996),while others have been detected in the ring galaxies NGC1097and NGC6951 (Barth et al.1995)and the dwarf galaxies NGC1569,NGC1705(O’Connell et al.1994), and He2-10(Conti&Vacca1994).While no generally accepted picture has emerged as to what conditions lead to the formation of young clusters,galaxy interactions appear to be an important component.It is particularly diﬃcult to determine the precise mechanism responsible for the presence of these objects in NGC1275because of the myriad peculiarities of this galaxy, including the presence of a signiﬁcant amount of dust,streamers of Hαemission,an active nucleus,and the location of the galaxy at the center of a coolingﬂow in the Perseus cluster. Two hypotheses have been oﬀered for the origin of these clusters,namely,that they were formed from the substantial mass deposition of the Perseus cluster coolingﬂow(200M⊙/yr) or that the cluster formation was triggered by a galaxy-galaxy interaction.Holtzman et al.(1992)preferred the latter hypothesis based on the observed lack of spread in the WFPC1colors,which implies a common age for the objects,and the appearance of a ripple in the galaxy light which suggests that a previous interaction may have occurred.Richer et al.(1993)found larger color spreads in high resolution CFHT images and preferred the coolingﬂow hypothesis.However,Holtzman et al.(1996)did not detect young clusters in three of a sample of four other coolingﬂow galaxies;the central cluster galaxy in Abell1795 may have a few clusters,but it also has a peculiar morphology which suggests a previous interaction.The merger hypothesis is particularly interesting in light of the theory that elliptical galaxies form through mergers and the observation that ellipticals have higher speciﬁc frequencies of globular clusters than spirals,where the speciﬁc frequency is a measure of the number of globular clusters per unit luminosity of the host galaxy.Ashman&Zepf (1992)investigate the proposition that clusters might form during mergers and suggest that,in such an event,cluster formation would occur in a brief burst,resulting in a set of newly formed clusters with a common age and color.This would lead to a cluster system with a bimodal distribution of cluster colors reﬂecting the diﬀerence in metallicity or age (or both)between the original and the newly formed clusters.They predict that the spatial distribution of the younger clusters would be more sharply peaked toward the center of thegalaxy than that of the old cluster system,because the old globular cluster populations of the two progenitor galaxies would remain spatially extended and probably be dynamically heated during the merger,while the new clusters would be formed out of gas which becomes more centrally concentrated during a merger.However,as Harris et al.(1995)note,an increase in speciﬁc frequency as a result of a merger requires not only that globular clusters form during such an event,but that they form preferentially over non-cluster stars as compared to the ratio of clusters to background stars in the progenitor galaxies.Few estimates of the speciﬁc frequency of these young cluster systems exist.Watson et al.(1996)suggest that the4young clusters in NGC253most likely have formed with a large speciﬁc frequency.In the merger remnant NGC3921Schweizer et al.(1996)ﬁnd that the blue clusters will increase the overall number of clusters enough that the galaxy will come to have the speciﬁc frequency of an elliptical ler et al.(1997)ﬁnd that the speciﬁc frequency of globular clusters in the merger remnant NGC7252will rise over the next15Gyr as the background population fades to resemble that of an elliptical. These results all suggest that interactions can increase the speciﬁc frequency in a galaxy.Luminosity functions of old globular cluster systems have been well studied and used as a part of the extragalactic distance scale because of their uniformity from galaxy to galaxy;they are roughly Gaussian in shape with a peak near M V=-7.3(Harris1996).The luminosity functions of most of the recently discovered young cluster systems are poorly determined because of either small number statistics(few young clusters in the galaxy)or incompleteness.A notable exception is the young cluster system in NGC4038/9,which shows no turnover to two magnitudes fainter than the turnover predicted for a typical old cluster system,even after allowing for the expected fading of the clusters based on stellar population models.Based on this,van den Bergh(1995)argues that this cluster system may be intrinsically diﬀerent from old globular cluster systems.However,Mateo (1993)notes that,at least in the LMC,the observed increasing cluster luminosity function is well modelled by a combination of globular and open clusters.Also,several authors have recently suggested that substantial numbers of clusters may be destroyed over a Hubble time(Gnedin&Ostriker1997;Elmegreen&Efremov1997);mechanisms include evaporation and tidal disruption by galactic bulges and disks.We have obtained WFPC2images of NGC1275which go about4magnitudes deeper (in the red)than the WFPC1observations of Holtzman et al.(1992).These observations provide more accurate colors than previous observations and probe the cluster population to approximately2.5magnitudes fainter than the turnover expected if this population is identical to the Galactic globular cluster system seen at an younger age.Section2brieﬂy summarizes the observations and the reductions.Section3discussesour analysis and potential sources of error.In section4we present our results including the photometry,luminosity function of the clusters,surface density distribution,an estimate of the speciﬁc frequency,and analysis of the sizes of the objects.2.Observations&Data ReductionObservations of NGC1275were made with the WFPC2on1995November16in the F450W and F702Wﬁlters.Exposure times in F450W were200,1000,and3×1300 seconds.In F702W the exposures were200,900,1000,and2×1300seconds.The F450W and F702Wﬁlters are roughly similar to broad band B and Rﬁlters.The data were reduced using the procedures discussed by Holtzman et al.(1995a). The individual exposures were all taken with a common pointing,and the frames in each color were combined.Cosmic rays were rejected in the averaging based on the expected variance from photon statistics and readout noise;an extra term was included in the expected variance which was proportional to the signal in the pixel to allow for small pointing diﬀerences between frames.3.AnalysisCombined color images of NGC1275in the PC and in the WFPC2ﬁelds are shown in Figures1a and1b,respectively.The nucleus is in the center of the PC,and the other bright point source in the PC is a foreground F star(Hughes&Robson1991).Almost all of the remaining point sources are candidate star clusters in NGC1275.To detect the compact clusters,we summed the two colors and subtracted a5×5 boxcar-smoothed version of this image.We divided this by the square root of the smoothed image to provide an image whose units were proportional to the local noise(assuming the noise is dominated by the background,as is the case here).We then used IRAF’s DAOFIND to detect objects on the resulting image,in order to provide a uniform detection threshold in signal-to-noise ratio across the image.The choice of detection threshold was determined by minimizing the number of spurious detections and maximizing the number of faint objects detected,judging from a visual inspection.Objects wereﬁltered by shape based on roundness and sharpness criteria computed by DAOFIND;we required-1< roundness<1and0.2<sharpness<1.Several areas of the frame were masked out, including the galaxy nucleus,the bright saturated star in the PC,and a few bright stars and galaxies in the WFs.Aperture photometry was performed using a1-pixel radius aperture in both the PC and the WFs.The small aperture was used to reduce background related errors,which are large in the central region of the galaxy.Sky values were determined by taking an estimate of the mode in a background annulus;in the PC,the annulus was2pixels wide with an inner radius of12pixels,while in each WF the corresponding annulus was3pixels wide with an inner radius of6pixels.We chose to use small sky annuli because the galaxy background is variable on small scales.Corrections from1-pixel apertureﬂux toﬂux within0.5′′were determined from the nine brightest sources.The average aperture corrections were1.03and1.15magnitudes in the PC frame for F450W and F702W,respectively,and0.63and0.71magnitudes in the WFs.These are slightly larger than the corrections for bright point sources measured by Holtzman et al.(1995a),but this is expected if these objects are slightly resolved.In the PC,measured aperture corrections varied on the order of0.05mag between diﬀerent objects.Measured variations in the aperture corrections for the individual WFs were∼0.02 mag,so an average aperture correction was assumed for all three.If there is an intrinsic spread in cluster sizes,using a single aperture correction for all objects would lead to systematic errors in the derived magnitudes.Toﬁrst order,however,colors are unaﬀected by such a spread.The transformations from HST magnitudes(F450W,F702W)to Cousins magnitudes(B,R)were made using the transformations given by Holtzman et al.(1995b).Foreground Galactic extinction in the direction of NGC1275was taken to be A B= 0.70(Burstein&Heiles1984).We determined the extinction in the WFPC2passbands by numerically integrating the product of an A star spectrum,theﬁlter transmission,the system response,and an extinction curve from Cardelli et al.(1989)derived assumingR V=3.1.An A star was used because of its similarity to the observed spectrum of the bright clusters.This gave A F450W=0.69and A F702W=0.40.These estimates do not include internal extinction,however,which may be important in NGC1275since patchy dust is evident;this is discussed further below.Potential photometry errors include intrinsic Poisson error in the signal,error in the aperture correction,and error in the background level determination.Typical errors were estimated from the simulated clusters from our completeness tests and are shown in Figure 2.The dashed lines in color and magnitude indicate input magnitudes for the artiﬁcial clusters.Completeness was estimated by generating simulated objects at each of9diﬀerent input magnitudes(23.75to27.75in B).The simulated objects were given the same noise characteristics as real objects.In the PC,1000objects were placed randomly in each of3 separate annuli to better model the variation of completeness with distance from the centerof the galaxy.Each set of artiﬁcial clusters was given a spatial distribution which mimicked the distribution of the brightest(B<25)blue and red clusters.In the WFs,the1000 artiﬁcial objects were placed randomly in a uniform distribution.On each chip,a PSF of one of the isolated bright clusters was used to create the simulated objects(the use of other objects gave comparable results).Two sets of artiﬁcial objects were placed to estimate the diﬀerence in detection eﬃciency for objects of two diﬀerent colors;the two sets of simulated clusters were given B-R=0.7and B-R=1.6,comparable to the colors of the observed cluster populations(next section).The derived average completeness(weighted by the spatial distribution of the observed clusters)as a function of B magnitude is shown in Figure3for the whole image as well as for the section which fell in the PC.We estimated the number of foreground stars based on the models of Bahcall and Soneira(1980)and expect<4objects with B<27in the PC.Since we expect such small numbers of foreground stars,we have neglected them.4.Results4.1.PhotometryWe present the photometry of all detected objects in NGC1275by plotting color against apparent magnitude in Figure4a.Extinction-corrected absolute magnitudes and colors are shown as well,using a distance of70.2Mpc determined by assuming pure Hubble ﬂow with H0=75km/s/Mpc.Weﬁnd1181blue objects(B-R<1.1)and1855red objects. Distinct red and blue populations are seen,although there is signiﬁcant color scatter. Roughly50%of the blue objects are seen in the PC,as compared to about15%of the red objects.These objects cannot be single stars because they are marginally resolved and because they are too bright.With the exception of the Shields-Filippenko object,the objects lack Hαemission(Holtzman et al.1992),which precludes their being emission line objects. Consequently,they are probably star clusters,as supported by spectroscopy of the brightest object(Zepf et al.1995).They are brighter and more compact than open clusters in the Galaxy;the brightest object is250times brighter than the brightest Galactic open cluster. Their closest analog seems to be globular clusters,although the inferred ages are much smaller(see below).To test whether the observed color scatter is likely to be related to internal extinction within NGC1275and photometric errors from errors in background subtraction,we show in Figure4b only clusters in the southwestern half of the PC frame which have estimatedphotometric errors of less than0.15mag in both B and R.This region was chosen because it contains fewer obvious signatures of dust than the northeastern region.In fact,weﬁnd that the spread in color among the blue objects in Figure4b is consistent with that associated with photometric errors(cf.Figure2),supporting the conclusion that the observed color spread within the two populations is likely to be caused by the variation of internal extinction in the environment of the galaxy,rather than diﬀerences in age.We conclude that the blue clusters are a single color,single age population,with the spread in colors coming from Poisson errors and background subtraction errors.Figure4b shows a distinct bimodality in the cluster population,consistent with the presence of two discrete populations.The blue clusters have a typical dereddened(B-R)0∼0.4.This is much bluer than typical old globular clusters,which have(B-R)0∼1.2(Harris1996).The uniformity of the colors suggests that the clusters were formed in a relatively short duration single burst rather than an ongoing or continuous process.Figure5shows the magnitude and color evolution of a single burst population for a variety of metallicities,assuming a Salpeter initial mass function from0.1to125M⊙and a total mass of1M⊙(Bruzual&Charlot 1993).If we compare the measured colors of the blue clusters in the PC to the models,we infer ages of107to109years,allowing for small possible systematic errors in the models and the data as well as the unknown metallicity of the objects.We note that the clusters are far too blue to be explained by a metallicity eﬀect alone.Ages younger than107years are ruled out by the absence of Hαemission from the clusters.Spectra of the clusters(Zepf et al.1995)argue for a several hundred Myr old population dominated in the blue by A type stars.It is also simply less probable that we that we should happen to observe these clusters at a younger age.The LMC has a number of compact clusters with comparable colors(van den Bergh 1981).These objects are substantially fainter than the brightest objects in NGC1275, implying that they are less massive.Still,observations of blue clusters in the LMC,where we can directly measure ages using the main sequence turnoﬀin color-magnitude diagrams, give us a less model dependent idea of the spread in colors that could be expected from a spread in ages.Figure6shows the distribution of B-V versus age for LMC clusters;ages are from Elson&Fall(1988)and Hodge(1981,1983),and colors from van den Bergh(1981). Between108and109years,we see that the integrated colors of the clusters cover a range of 0.3in B-V.This argues against a large spread in the ages for the NGC1275clusters,which show no such spread in colors.While our observations were in B and R,not B and V,the color spread in B-R for the same age range would be0.8magnitudes,assuming a V-R vs B-R relation from the population synthesis models.Given ages,we can estimate masses for the clusters based on their luminosities.Age estimates of108and109years give mass estimates for the brightest object of2×107and 108M⊙,respectively.Blue clusters at our completeness limit of B=27have masses of2×104to105M⊙.These masses are very comparable with those of Milky Way globulars, which typically have masses between104and3×106M⊙,with a handful of clusters with M<104M⊙(Mandushev,Spassova,&Staneva1991,Pryor and Meylan1993).Our mass estimates depend on the assumption of a Salpeter IMF.Two of the three brightest objects in the southwest half of the PC(Figure4b)have much redder colors than the rest of the blue clusters(B-R of0.95and1.23).While these objects are close to the nucleus,they are bright enough that errors in determining the galaxy background are not a large source of error.Possible explanations are reddening by dust,a younger age(slightly less than107years old)when the integrated light is dominated by red supergiants(Leitherer&Heckman,1995),or the identiﬁcation of these objects with late type foreground stars.For the redder object,the last interpretation is supported by our measurement of sizes(§4.5),since it appears to be unresolved while almost all other objects appear marginally resolved.We suggest that the objects with B-R∼1.6(∼1.3dereddened)are the old population of globular clusters around NGC1275.These are slightly redder than Galactic globular clusters which have an average(B-R)0∼1.2.The brightest(M B=-10.7)has a magnitude similar to the brightest globulars seen in other central cluster galaxies.4.2.Luminosity FunctionFigure7a shows the B luminosity function for the blue clusters(B-R<1.1),and Figure7b shows the B luminosity function for the red clusters(B-R>1.1).The dotted lines in each plot show the results after correction for incompleteness.The luminosity function of the blue clusters looks distinctly diﬀerent from that expected for a typical old globular cluster population at a younger age.While the Galactic globular cluster luminosity function is Gaussian in shape with peak at M B∼-6.6andσ=1.0mag(Harris1996),the luminosity function for the clusters in NGC1275is more closelyﬁt by a exponential.If we were to observe the current Galactic globular cluster system at an age of500million years and at the distance of NGC1275(and the same Galactic extinction),we would observe a turnover in the luminosity function at B∼24(H0=75km/s/Mpc).This prediction assumes4magnitudes(13Gyr)of fading as suggested by the models of Bruzual&Charlot (1993).Our photometry is complete at the50%level to3magnitudes fainter than this,yet there is no evidence of a turnover in the luminosity function of the clusters in NGC1275.The luminosity function of the blue clusters has the same trend as that of Galactic open clusters,namely,an increasing number of clusters at fainter magnitudes with no turnover (van den Bergh and LaFontaine1984).However,the most luminous clusters in NGC1275 are brighter than any observed Galactic open clusters,despite being older than the brightest of them.The compactness as inferred from the HST images is also diﬀerent from that of open clusters(§4.5).Mateo(1993)ﬁnds that an increasing luminosity function for clusters in the LMC can be produced by a mixed population of true globulars and open clusters.In NGC1275,a similar explanation would require a large number of open clusters which are far more massive than any Galactic open clusters.Consequently,as a system,these clusters are diﬀerent from any cluster system seen in Local Group galaxies.As individual objects, however,the physical properties appear most similar to globular clusters.In Figure8,we compare the luminosity function of clusters in NGC1275with the luminosity functions in several of the other galaxies where reasonable numbers of blue clusters are found,as well as with the luminosity functions of Milky Way clusters.Dashed lines show rough completeness limits for the diﬀerent observations,and dotted lines give the location of the expected turnover given the various age estimates of the clusters.There is no strong evidence in any of the young cluster systems for an intrinsic turnover in the luminosity function.If these objects will evolve to look like the Galactic globular cluster system,some mechanism must preferentially destroy low luminosity,low mass clusters on timescalesof13Gyr.Two possibilities are tidal disruption and evaporation(Gnedin&Ostriker 1997;Elmegreen&Efremov1997).For tidal disruption to preferentially destroy low mass clusters,such clusters must have a lower mean density than more massive clusters. Evaporation through two-body relaxation can preferentially destroy lower mass clusters as their stars escape the cluster potential well and are captured by the gravitational potential well of the galaxy.Gnedin and Ostriker(1997)predict that from half to three quarters of the initial globular cluster population in a galaxy may be destroyed by a combination of these processes in a Hubble time.4.3.Surface Density ProﬁleFigure9shows the surface density distribution of red and blue clusters(open triangles andﬁlled triangles,respectively).Corrections have been made for incomplete annuli at large radii,for masked areas,and for diﬀering completeness levels with distance from the bright galaxy center.Error bars are simple Poisson errors in counts of clusters.The central area,within18pixels(0.8arcsec)from the core of the galaxy,has been omitted from thesurface density proﬁle due to the bright nucleus.It is clear that the blue clusters are more centrally concentrated than the red ones.Weﬁt the surface density distribution of the blue and red cluster systems from4′′to120′′with power laws.For the blue clusters,weﬁnd that a power law slope of-1.3 provides a reasonableﬁt over the entire range.For the red clusters,we note aﬂattening in the inner portion of the distribution andﬁt the surface density with two power laws. Inside0′.5,we measure a slope of-0.6,while outside0′.5weﬁnd a slope of-1.0.Flattening in the central part of the surface density distribution of a globular cluster system is also seen in other similar galaxies,such as M87(McLaughlin1995)and NGC5128(Harris et al.1984).Our measurements for the distribution of old clusters are in good agreement with those of Kaisler et al.(1996).However,they adopt a power law slope of-1.3,based on the observational relation between galaxy magnitude and power law slope of the surface density distribution of the globular cluster system(Harris et al.1986,1993).We note that our measured outer slope is sensitive to the choice of break point between the inner and outer regions;the data show a sign of steepening even more in the outermost parts. The spatial distribution of the clusters agrees with the galaxy merger model of Ashman and Zepf(1992),which predicts that the younger clusters will be peaked towards the center of the galaxy,while the older clusters will be moreﬂattened in their distribution.4.4.Speciﬁc FrequencyThe speciﬁc frequency of globular clusters in a galaxy is given byS N=N T100.4(15+M V)(Harris and van den Bergh1981)where N T is the total number of clusters and M V is the absolute V magnitude of the galaxy.This is of interest in light of the hypothesis that elliptical galaxies form via mergers of spirals and the observation that ellipticals havea higher speciﬁc frequency of globular clusters than spirals.Consequently,the merger hypothesis requires that globular clusters form during mergers with a higher speciﬁc frequency than that of the progenitor population.Also,it requires that clusters form in numbers comparable to those of the old cluster population(Zepf&Ashman1993).To address these questions,we calculate the speciﬁc frequency of the old population,the current speciﬁc frequency of the merger related population,and the predicted speciﬁc frequency of the merger related population in13Gyr.To calculate speciﬁc frequencies,we need to estimate the total number of clusters。

舍维尼玛科宝

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Even ultra-highpressure water jetting according to ISO 8501-4 Wa 2 with a maximum flash rust grade M is also acceptable.Old coatings: In case of well adhering coating systems, careful cleaning (e.g. by water jetting) is sufficient. Loose particles must be removed, damaged areas should be minimum prepared in accordance with PSa 2, PMa or PSt 2 and primed with Macropoxy ® Primer HE N.The required surface preparation/cleaning and compatibility of thesystem should be determined with trial areas.Stir component A very thoroughly using a mechanical paint mixer (start slowly, then increase up to approx. 300 rpm). Add component B carefully and mix both components very thoroughly (including sides and bottom of the container). Mix for at least 3 minutes until a homogeneous mixture is achieved. We recommend to fill the mixed material into a clean container and mix again shortly as described above to avoid incorrect mixing. 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However, the operating pressure should be the lowest possible consistent satisfactory atomisation.As conditions will vary from job to job, it is the applicators responsibility to ensure that the equipment in use has been set up to give the best results.If in doubt consult Sherwin-Williams customer service.Conventional SprayAtomising Pressure: 3 - 5 bar (43 - 73 psi)Tip Size: 1.5 – 2.5 mm (0.06 – 0.10 inch)Brush and Roller• Surface preparation St 2 or St 3• With brush application best penetration and surface wetting is achievedRevised 07/2023 Issue 1HIGH SOLIDS, SURFACE-TOLERANT EPOXY PRIMERSteel resp. patch up of spots on hot-dip galvanized surfaces 2 x Macropoxy ® Primer HE NOvercoatable with 1- and 2-pack coatings e.g Macropoxy ®, Acrolon ® and Kem Kromik ®, provided the surface to be coated is clean, dry and free from contamination.Example Blatt 941 x Macropoxy ® Primer HE N 1 x Macropoxy ® EG-1 VHS1 x Acrolon ® EG-4 or Acrolon ® EG-5Old coatingsMacropoxy ® Primer HE N can be used on a variety of sound 1-pack and 2-pack coats for refurbishment.Note: Macropoxy ® Primer HE N is not recommended for permanentimmersion.Drying times, curing times and pot life should be considered as a guide only.Epoxy Coatings - Tropical UseEpoxy coatings at the time of mixing should not exceed a temperature of 35ºC. Use of these products outside of the pot life may result in inferior adhesion properties even if the materials appear fit for application. Thinning the mixed product will not alleviate this problem. If the air and substrate temperatures exceed 40ºC and epoxy coatings are applied under these conditions, paint film defects such as dry spray, bubbling and pinholing etc. can occur within the coating.Chemical resistance:Resistant to weathering, de-icing salts, oils and grease and short term exposure to fuels and solvents.Temperature resistance:Dry heat up to + 150°C, short term up to + 200°C.Increased humid ambient temperature up to + 40°C.Numerical values quoted for physical data may vary slightly from batchto batch.Consult Product Health and Safety Data Sheet for information on safestorage, handling and application of this product.Whilst all statements made about our products (whether in this data sheet or otherwise) are correct and accurate to the best of our knowledge, we have no control over the quality or the condition of the substrate, the application conditions or the many other factors affecting your use and application of our product.The appropriateness of the product under the actual conditions ofapplication or intended use must be determined exclusively by you. 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Test of the Pioneer anomaly with the Voyager 2 radio-ranging distance measurements to Uranu

a rXiv:g r-qc/68127v 129Aug26Test of the Pioneer anomaly with the Voy-ager 2radio-ranging distance measurements to Uranus and Neptune Lorenzo Iorio Viale Unit `a di Italia 68,70125Bari,Italy tel./fax 00390805443144e-mail:lorenzo.iorio@libero.it Abstract In this paper we test the hypothesis that the Pioneer anomaly can be of gravitational origin by comparing the predicted model-independent shifts ∆a/a for the semimajor axis of Uranus and Neptune with the Voyager 2radio-technical distance measurements performed at JPL-NASA.As in the case of other tests based on diﬀerent methods and data sets (secular perihelion advance,right ascension/declination resid-uals over about one century),the orbits of the investigated planets are not aﬀected by any anomalous acceleration like that experienced by the Pioneer 10/11spacecraft.Keywords:gravity tests;Pioneer anomaly;planets PACS:04.80Cc 1Introduction The Pioneer anomaly (Anderson et al.1998;2002)consists of an unex-pected,almost constant and uniform acceleration directed towards the SunA Pio =(8.74±1.33)×10−10m s −2(1)detected in the data of both the spacecraft Pioneer 10(launched in March 1972)and Pioneer 11(launched in April 1973)after they passed the thresh-old of 20Astronomical Units (AU;1AU is slightly less than the average Earth-Sun distance and amounts to about 150millions kilometers).Latest communications with the Pioneer spacecraft,conﬁrming the persistence of such an anomalous feature,occurred when they reached 40AU (Pioneer 11)and 70AU (Pioneer 10).1If the Pioneer anomaly is of gravitational origin,it must then fulﬁl the equivalence principle,which is presently tested at a10−12level(Will2006) and lies at the foundations of the currently accepted theories of gravity.In its weak form,it states that diﬀerent bodies fall with the same accelerations in a given external gravitationalﬁeld.As a consequence,an extra-gravitational acceleration like A Pio should also aﬀect the motion of any other object mov-ing,at least,in the region in which the Pioneer anomaly manifested itself.In this context,many models have been proposed in order toﬁnd some possible gravitational explanation of the anomalous acceleration experienced by the Pioneer10/11spacecraft.E.g.,Jaekel and Reynaud(2005)put forth a metric linear extension of general relativity which yields an acceleration only aﬀecting the radial component of the velocity of a test particle.Brown-stein and Moﬀat(2006)used an explicit,analytical modelﬁtted to all the presently available Pioneer10/11data points.The availability of•The latest observational determinations of the secular,i.e.averaged over one orbital revolution,extra-advances of perihelia˙̟of the inner (Pitjeva2005a)and of some of the outer(Pitjeva2006a)planets of the Solar System•The residuals of the direct observablesαcosδandδ,whereαandδare the right ascension and the declination,respectively,for the gaseous giant planets and Pluto(Pitjeva2005b)processed at the Institute of Applied Astronomy,Russian Academy of Sci-ences(IAA,RAS)has recently allowed to•Perform clean and unambiguous tests of the possibility that the ac-celeration of eq.(1)can also aﬀect the planetary motions in the far1 regions of the Solar System(Iorio2006a;Iorio and Giudice2006)•Dismiss the previously cited mechanisms for the anomalous Pioneer behavior(Iorio2006b;2006c)In this letter we perform a further,independent test of the hypothesis that the Pioneer anomaly can be of gravitational origin by exploiting certainshort-period,i.e.not averaged over one revolution,features of the semimajor axes a of Uranus and Neptune and the radar-ranging distance measurements to them performed at Jet Propulsion Laboratory (JPL),NASA,during their encounters with the Voyager 2spacecraft (Anderson et al.1995).The outcome of such a test is consistent with the other ones based on ˙̟(Iorio 2006a;2006c)and αcos δ−δ(Iorio and Giudice 2006):an acceleration like that of eq.(1)does not aﬀect the motion of Uranus and Neptune.2The eﬀect of a Pioneer-like acceleration on thesemimajor axis and comparison with the obser-vationsIn (Iorio and Giudice 2006)there are the analytical expressions of the short-period shifts induced on the Keplerian orbital elements by a radial,constant perturbing acceleration A r ,whatever its physical origin may be.For the semimajor axis we have∆aGM (cos E −cos E 0)=−2e 1−e 2A rr 2 =GM1−e 2(3)is the Newtonian acceleration averaged over one orbital period and E is the eccentric anomaly which can be expressed in terms of the mean anomaly M as (Roy 2005)E ∼M + e −e 32sin 2M +3a =0,(5)so that ∆a/a cannot tell us anything about the impact of an acceleration like A Pio for those planets for which data sets covering at least one full orbital revolution exist.To date,only Neptune (P =164yr)and Pluto3(P=248yr)have not yet described a full orbit since modern astronomical observations became available after theﬁrst decade of1900.Incidentally,let us note that2,according to eq.(2),∆a/a=0for e=0.The situation is diﬀerent for Neptune since no secular eﬀects can yet be measured for it.Thus,let us use eq.(2)and eq.(1)for A r getting∆aa(optical)Nep=(1−3)×10−6.(7)It must be compared with eq.(6)at3JD=2448000.5(E=107.423deg)∆aaNep(JD=2447763.67)=(−0.7954±0.1210)×10−6.(9)By assuming for∆a the residuals with respect to the DE200JPL ephemerides used in Table1of(Anderson et al.1995),i.e.8224.0±1km,one gets∆a2In the circular orbit limit,Anderson et al.(1998;2002)use the erroneous formula ∆a/a=−A r/A N and apply it to Mars and the Earth to show that an extra-acceleration like A Pio cannot exist in that regions of the Solar System.3For Neptune E0=128.571deg at JD=2451545.0.4This clearly rules out the prediction of eq.(9).The same analysis can also be repeated for Uranus(P=84.07yr)for which no modern data covering a full orbital revolution were available at the time of the Anderson et al.(1995)work;as for Neptune,one radar-ranging distance measurement is available from the Voyager2ﬂyby with Uranus (JD=2446455.25).The prediction of eq.(2),with eq.(1)for A r,for the ﬂyby epoch4(E=8.860deg)is∆aa(ranging)Ura(JD=2446455.25)=(0.0513±0.0003)×10−6.(12)Also in this case,the eﬀect which would be induced by A Pio on∆a/a is absent.It maybe interesting to note that the paper by Anderson et al.(1995) has been used as a basis for other tests with the outer planets using diﬀerent methods.E.g.,Wright(2003)and Sanders(2006)adopt the third Kepler’s law.Basically,the line of reasoning is as follows.In the circular orbit limit, let us write,in general,P=2πa/v;in particular,the third Kepler law states that P=2πK p =∆A4For Uranus E0=70.587deg at JD=2451545.0. 5E.g.due to dark matter(Anderson et al.1995).5al.1995),∆K p/K meas=(−2.0±1.8)×10−6,while A Pio/A N=(−133.2±p20.3)×10−6.As can be noted,also in this case,the answer is negative but the accuracy is far worse than in our test.3Discussion and conclusionsIn this paper we have used the NASA-JPL radio-technical ranging mea-surements to Uranus and Neptune performed during the Voyager2ﬂybies (Anderson et al.1995)in order to make a model-independent test of the hypothesis that an anomalous acceleration of gravitational origin like that detected in the data of the Pioneer10/11spacecraft may also aﬀect the or-bital motion of such planets.The answer is neatly negative,as in previous tests involving the perihelion secular advance of Uranus(Iorio2006a;2006c) and the right ascension/declination residuals of Uranus,Neptune and Pluto over about one century(Iorio and Giudice2006).Thus,in regard to the celestial bodies lying at the edge of the region in which the Pioneer anomaly manifested itself(∼20−70AU),or entirely residing in it,the present-day situation can be summarized as follows •Uranus(a=19.19AU).3model-independent tests–Secular advance of perihelion(almost one century of optical dataprocessed at IAA,RAS):negative–Right ascension/declination residuals(almost one century of op-tical data processed at IAA,RAS):negative–Short-period semimajor axis shift(1radar-ranging measurementat epoch JD=2446455.25by JPL,NASA):negative •Neptune(a=30.08AU).2independent tests–Right ascension/declination residuals(almost one century of op-tical data processed at IAA,RAS):negative–Short-period semimajor axis shift(1radar-ranging measurementat epoch JD=2447763.67by JPL,NASA):negative •Pluto(a=39.48AU).1test–Right ascension/declination residuals(almost one century of op-tical data processed at IAA,RAS):negative6In all such tests the observationally determined quantities−obtained at JPL and IAA independently and without having the Pioneer anomaly in mind at all−have been compared to unambiguous theoretical predictions based on the eﬀects induced by a radial,constant and uniform acceleration with the same magnitude of that experienced by Pioneer10/11,without making any assumptions about its physical origin.In addition,we may also consider the perihelion-based negative tests for Jupiter(a=5.20AU)and Saturn(a=9.53AU)(Iorio2006c),based on the model by Brownstein and Moﬀat(2006)ﬁtted to all the presently available data points of Pioneer10/11.In conclusion,it seems more and more diﬃcult to accept the possibility that some modiﬁcations of the current laws of Newton-Einstein gravity may be the cause of the Pioneer anomaly.AcknowledgementsI thank Edward L.(Ned)Wright for useful correspondence about the radar-ranging distance measurements of Uranus and Neptune and for the reference to his webpage.References[1]Anderson,J.S.,Lau,E.L.,Krisher,T.P.,Dicus,D.A.,Rosenbaum,D.C.,and Teplitz,V.L.,Improved Bounds on Nonluminous Matterin Solar Orbit,Astroph.J.,448,885-892,1995.[2]Anderson,J.D.,Laing,P.A.,Lau,E.L.,Liu,A.S.,Nieto,M.M.,and Turyshev,S.G.,Indication,from Pioneer10/11,Galileo,andUlysses Data,of an Apparent Anomalous,Weak,Long-Range Ac-celeration,Phys.Rev.Lett.,81,2858-2861,1998.[3]Anderson,J.D.,Laing,P.A.,Lau,E.L.,Liu,A.S.,Nieto,M.M.,andTuryshev,S.G.,Study of the anomalous acceleration of Pioneer10and11,Phys.Rev.D,65,082004,2002.[4]Brownstein,J.R.,and Moﬀat,J.W.,Gravitational solution to thePioneer10/11anomaly,Class.Quantum Grav.,23,3427-3436,2006.[5]Iorio,L.,The Lense-Thirring eﬀect and the Pioneer anomaly:SolarSystem tests,paper presented at The Eleventh Marcel Grossmann7Meeting on General Relativity,23-29July,Freie Universit¨a t Berlin, 2006,/abs/gr-qc/0608105,2006a.[6]Iorio,L.,On a recently proposed metric linear exten-sion of general relativity to explain the Pioneer anomaly, /abs/gr-qc/0608068,2006b.[7]Iorio,L.,On a recently proposed scalar-tensor-vector metric ex-tension of general relativity to explain the Pioneer anomaly, /abs/gr-qc/0608101,2006c.[8]Iorio,L.,and Giudice,G.,What do the orbital motions of the outerplanets of the Solar System tell us about the Pioneer anomaly?, New Astron,11,600-607,2006.[9]Jaekel,M.-T.,and Reynaud,S.,Gravity tests in the solar systemand the Pioneer anomaly,Mod.Phys.Lett.A,20,1047-1055,2005.[10]Pitjeva,E.V.,Relativistic Eﬀects and Solar Oblateness from RadarObservations of Planets and Spacecraft,Astron.Lett.,31,340-349, 2005a.[11]Pitjeva,E.V.,High-Precision Ephemerides of Planets-EPM and De-termination of Some Astronomical Constants,Sol.Sys.Res.,39, 176-186,2005b.[12]Pitjeva,E.V.,private communication2006a.[13]Pitjeva,E.V.,private communication2006b.[14]Roy,A.E.,Orbital Motion.Fourth Edition,Institute of Physics Pub-lishing,Bristol,2005.[15]Sanders,R.H.,Solar system constraints on multiﬁeld theories ofmodiﬁed dynamics,Mon.Not.Roy.Astron.Soc.,370,1519-1528, 2006.[16]Will, C.M.Living Rev.Relativity,9,3,2006./lrr-2006-3.[17]Wright, E.L.,Pioneer Anomalous Acceleration,/ wright/PioneerAA.html,2003.8。

A large X-ray flare from the Herbig Ae star V892 Tau

a rX iv:a st r o -p h /0310355v 1 14 O c t 2003Send oﬀprint requests to :G.Giardino,ggiardin@rssd.esa.intpossess either a strong stellar wind nor a corona (as no magnetic dynamo mechanism is available).In contrast Herbig Ae/Be stars appear to possess a strong stellar wind (Skinner et al.1993;Bouret et al.1997)and a magnetic dynamo associated with an outer convection zone has been invoked to explain the periodic variation of the emission lines (Praderie et al.1986)as well as the stellar wind itself (Finkenzeller &Mundt 1984).Zinnecker &Preibisch (1994)proposed that the ob-served X-ray luminosity is linked to the stars’strong stel-lar winds,possibly originating in shocks due to wind insta-bilities and/or in the collision between the fast wind and the remnant circumstellar material.Damiani et al.(1994)also favored a stellar wind origin for the X-ray emission from Herbig Be stars.Nevertheless a magnetically heated corona could also be at the origin of the observed X-ray emission (Zinnecker &Preibisch 1994).The presence of winds and the possibility of magnetic activity make these objects interesting targets for X-ray studies.The unambiguous detection of ﬂaring activity in any Herbig Ae/Be star would be signiﬁcant as it would provide indirect but strong evidence for the presence of a magnetically conﬁned corona and thus of an operational dynamo mechanism.So far there is only one reported observation of ﬂar-ing activity in an Herbig Be star:Hamaguchi et al.(2000)performed ASCA observations of the Herbig Be starMCW297,and reported the detection of a largeﬂare during which the X-ray luminosity of the source increasedby a factor of5,with the plasma temperature increas-ing from2.7keV during the quiescent phase to6.7keV atﬂare maximum.The interpretation however is aﬀectedby some ambiguity due to the large ASCA point spreadfunction(PSF).Testi et al.(1998)found about20infrared sources in the ASCA error circle around MWC297,themajority of which are likely to be low-mass protostars.The peak X-ray luminosity of≃5×1032erg s−1reported byHamaguchi et al.(2000)would correspond to a very large–but still possible–ﬂare for a typical low-mass active T Tauri.For example Tsuboi et al.(1998)have reportedASCA observations of a largeﬂare from the Weak-linedT Tauri star(WTTS)V773Tau,in which the peakﬂare luminosity was at least∼1033erg s−1.The MWC297event therefore would not be exceptional for a low mass pre-main-sequence star.Hamaguchi et al.(2002b)have re-cently re-observed MWC297with Chandra,ﬁnding thesource hundred times less luminous in X-rays than esti-mated from ASCA observation,and with no evidence forvariability,thus casting some doubts on the original inter-pretation.In this article we report the observation of a large X-rayﬂare from the Herbig Ae star V892Tau.We have used publicly available XMM-Newton and Chandra datato monitor the X-ray activity of V892Tau and during one of the two XMM-Newton exposures a largeﬂare isobserved.While the apparent companion of V892Tau,V892Tau NE,is unresolved by the XMM-Newton PSF, as discussed later,the evidence that the observedﬂare iscoming from the Herbig Ae star is compelling.The present paper is organized as follow:after a briefintroduction of the properties of V892Tau below,the ob-servations are described in Sect.2.The spectral and tim-ing analysis of the data are presented in Sect.3and theresults are discussed in Sec.4.1.1.The Herbig Ae star V892TauV892Tau–also known as Elias1–is a young stellar ob-ject located in the Taurus dark cloud complex,and is sup-posed to be the source of the illumination for the faint neb-ula IC359.The apparent magnitude of V892Tau is R=13.14(Strom&Strom1994)and its spectral classiﬁcation varies from B9(Strom&Strom1994)and A0(Elias1978;Finkenzeller&Mundt1984)to A6(Cohen&Kuhi1979, Berrilli et al.1992,The et al.1994).Estimates for the vi-sual extinction also vary from A V∼8(Elias1978)and A V=8.85(Strom&Strom1994,derived from a simul-taneous estimate of the spectral type and of the apparentcolor,R−I=1.71)to A V∼3.9(Zinnecker&Preibisch 1994).The star is usually placed at a distance of140pc because of its association with the Taurus dark clouds (Elias1978).The bolometric luminosity of V892Tau is L∼38L⊙(Berrilli et al.1992)and the source is variable in the near-infrared(Elias1978).Through near-infrared speckle interferometry Kataza&Maihara(1991)resolved V892Tau into an unresolved core and a sub-arcsec structure elongated in the east-west direction.They interpret the light of the elongated structure as being reﬂected within an edge-on circumstellar disk of moderate optical depth.Newer near-infrared speckle interferometry observations were performed by Haas et al.(1997),who favor a scenario in which the diﬀuse component is due to scattering in bipolar lobes with a polar axis oriented east-west.V892Tau appears to be a binary system(Leinert et al. 1997).The apparent stellar companion,hereafter referred to as V892Tau NE,lies4.1arcsec to the northeast,at po-sition angle22◦1(Skinner et al.1993).The available mea-surements allow a tentative classiﬁcation of V892Tau NE as a WTTS with spectral type M2reddened by8–12mag of visual extinction(Leinert et al.1997).The study by Leinert et al.(1997),based on speckle interferometry,was carried out with the explicit purpose of detecting binaries among Herbig Ae/Be stars.Leinert et al.(1997)achieved a resolution of∼0.1arcsec,that at a distance of140pc correspond to14AU,and they do not detect other stars in the vicinity of V892Tau.They conclude that in the near-infrared V892Tau is basically a wide binary system.2.ObservationsThe X-ray observations discussed in this paper were ob-tained with the XMM-Newton and the Chandra obser-vatories.The XMM-Newton observations of V892Tau consists of two deep(74.4and45.1ks nominal)consec-utive exposures,theﬁrst starting on March112001at 12:40:22UT and the second one starting on March12 2001at10:23:10UT.All three EPIC cameras were active at the time of the observations,in full-frame mode with the mediumﬁlters.The Principal Investigator for these observations is F.Walter and the observation target is the triple WTTS system V410Tau.The observations are publicly available from the XMM-Newton archive.The raw XMM-Newton data have been processed by us with the standard SAS V5.4.1pipeline system,concentrat-ing,for the spectral and timing analysis,on the EPIC-pn camera.In each of the two XMM-Newton exposures the background is aﬀected by a large protonﬂares of more than10ks of duration.We have retained only time inter-vals in which the count rate for the whole frame of pho-tons above5keV was below a certain threshold(3.3cts/s in the present case).This operation omits roughly30%of the observing time,but eﬀectively reduces the background level by a factor of≃4.Source and background photons were extracted using a set of scripts purposely developed at PalermoObservatory.Source and background regions were deﬁned interac-tively in the ds9display software,with the background extracted from regions on the same CCD chip and at the same oﬀ-axis angle as for the source region.Response matrices(“rmf and arfﬁles”)appropriate for the posi-tion and size of the source extraction regions were com-puted.The spectral analysis has been performed using the XSPEC package,after rebinning the source spectra to a minimum of20source counts per(variable width)spectral bin.The Chandra ACIS observation of V892Tau was taken starting on March72002at6:15:28UT(18.0ks nomi-nal).The Principal Investigator for these observations is P.Predehl and also in this case the observation target is V410Tau2.The data were retrieved from the public data archive,with no re-processing done on the archival data. Source and background regions were deﬁned in ds9,and light curves and spectra were extracted from the cleaned photon list using CIAO V.2.2.1threads,which were also used for the generation of the relative response matrices. Spectral analysis was performed in xspec in the same way as for the XMM-Newton spectra.Fig.1shows the images of the V892Tau system in the Chandra ACIS camera and XMM-Newton EPIC-pn cam-era(before and after the largeﬂare)as well as the Palomar Digital Sky Survey image of theﬁeld.The4images are on the same sky coordinate scale.The source at the cen-tre of the images is the V892Tau system.V892Tau and V892Tau NE are clearly resolved in the Chandra observa-tions.The XMM-Newton point spread function has a full width at half maximum of15arcsec and therefore cannot resolve the system.The source at38arcsec to the SE of the V892Tau system is[BHS98]MHO11,a T Tauri star (Brice˜n o et al.1998),ﬁrst identiﬁed in ROSAT data by Strom&Strom(1994).The bright source in the North-East corner is Hubble4,a well known T Tauri.In Table1we report the coordinates of V892Tau and V892Tau NE as derived from the radio(VLA)observation of Skinner et al.(1993),to be compared with the coordi-nates of the sources in the XMM-Newton and Chandra data.The source coordinates from the EPIC-pn data cor-respond to the peak of a gaussian distributionﬁtted to the source image,the source coordinates for the Chandra data simply correspond to the brightest pixel in the source im-age.The agreement between the sources’positions in the Chandra image and as determined from VLA observations is excellent(within0.4arcsec).The source coordinates derived from the XMM-Newton observations before the ﬂare have a2.4arcsec oﬀset from V892Tau(well within the uncertainty expected for the determination of posi-tions of EPIC X-ray sources)and a6arcsec oﬀset from V892Tau NE.After theﬂare the position oﬀsets become4:18:4038364244464828:20:003019:0018:304:18:4038364244464828:20:003019:004:18:4038364244464828:20:003018:304:18:4038364244464828:20:003019:0018:30Fig.1.The ﬁeld centered on the system V892Tau and V892Tau NE in the EPIC-pn camera before the ﬂare (top left)and during the ﬂare (top right),in the ACIS camera (bottom left)and in the Digital Sky Survey (bottom right).The images are on the same coordinate scale.The system is resolved in the Chandra data.The source at the south-east of the V892Tau system is [BH98]MHO 11,a T Tauri star,the source at North-East is Hubble 4,also a T Tauri.Table 1.Positions for the two components of the V892Tau system from radio (VLA)observations (Skinner et al.1993)and as derived here from XMM-Newton and Chandra images.SourceVLAXMM aXMM bChandraV892Tau 41840.6041840.6741840.6741840.63281915.9281913.7281912.9281915.8V892Tau NE41840.70c c 41840.74281919.7cc281919.3aX-ray quiescent,b X-ray ﬂaring,c unresolved from V892Tau.3.2.XMM-Newton observationsThe light curve of the V892Tau system derived from the two consecutive XMM-Newton exposures are shown in Fig.4.All the gaps in the light curve except the one around 64ks are due to the ﬁltering process that we have applied to the raw data in order to remove the eﬀect of solar proton ﬂares.In particular roughly 10ks at the be-ginning of the ﬁrst exposure have been removed.The gap around 64ks is due to the time diﬀerence between the end of the ﬁrst exposure and the start of the second (one hour).During the ﬁrst ∼80ks the light curve of the V892Tau-V892Tau NE system presents signiﬁcant vari-ability with a time scale and amplitude similar to the one observed for V892Tau in the Chandra data.During the last 30ks the light curve of the system undergoes a dra-matic variation,in what appears to be a large ﬂare.The source counts increases by a factor of ∼8in less than 10ks.The source ﬂux then remains at around the maximum level until the end of the XMM-Newton exposure.We have performed the spectral analysis of the two XMM-Newton exposures separately and we summarise the results into two separate tables:Table 2for the ﬁrst ex-Fig.2.Background-corrected light curves of V892Tau (top)and V892Tau NE(bottom)from the Chandra data, where the two stars are well resolved.Note the diﬀerent vertical scale.posure and Table3for the second exposure.The reasonfor this is that while for theﬁrst exposure two tempera-ture plasma models are necessary to obtain acceptableﬁts to the spectra for the second exposure one-temperatureplasma models provide adequateﬁts to the spectral data.The spectrum of the V892Tau system during theﬁrstexposure of74ks,corresponding to an eﬀective integra-tion time of<∼64ks(after the protonﬂareﬁltering pro-cess),is shown in Fig.5,together with the bestﬁt ab-sorbed2temperature plasma model.The bestﬁt valuesfor the model parameters are summarised in Table2to-gether with the reducedχ2of theﬁt and its null hypothesis probability,P.A model with an absorbing column density of N(H)=0.92×1022cm−2,plasma temperatures kT1= 1.02keV and kT2=2.82keV and a metal abundance Z=0.21provides a goodﬁt to the integrated spectrum. An absorbed one temperature plasma model(as used for the Chandra data,which however have lower statistics) does not provide an acceptable description of the spec-trum.Nevertheless a two temperature plasma model with a metal abundance and two plasma temperatures frozen Fig.3.Background-corrected spectra of V892Tau(top) and V892Tau NE(bottom),from the Chandra data.The best-ﬁt absorbed1-T models are also shown.at the values above(Z=0.21,kT1=1.02keV and kT2= 2.82)provides a goodﬁt to the Chandra data(P=0.72) by letting the two emission measures and the absorbing column density vary–see Table2.Theﬁtted values for the two emission measures are EM1=(4.3±1.6)×1053cm−3 and EM2=(2.2±0.4)×1053cm−3,consistent with the values derived from the XMM-Newton spectrum.The rel-ative modelﬂux level is7.3×10−13erg cm−2s−1(in the 0.55–7.50keV band).The value for the absorbing col-umn density derived in this way from the Chandra data, N(H)=(1.24±0.09)×1022cm−2is higher than the value derived from XMM-Newton(and a model with the value derived from XMM-Newton does not provide an ac-ceptable description of the data).We note though that a systematically higher value for the absorbing column density derived from Chandra data is consistent with the known presence of(likely carbon-based)contamination on the ACIS chips.This causes additional low-energy absorp-tion(up to50%near the C edge)not accounted for in the current response matrices(Plucinsky et al.2003).Given the source variability during these∼64ks of observation,we have investigated the presence of signiﬁ-cant spectral variation.We have subdivided the data into three intervals(theﬁrst30ks,the following18ks and theﬁnal16ks),chosen to ensure similar statistics in the resulting spectra.As the initial part of the observation israther heavily contaminated by high background,a higher fraction of it was discarded,and therefore theﬁrst inter-val is signiﬁcantly longer.The three spectra were modeled with an absorbed two temperature plasma model.The ﬁtted values of the model parameters are summarised in Table2.As it can be seen by inspecting the table,the short term variability observed in the system V892Tau during thisﬁrst XMM-Newton observation does not appear to be associated with signiﬁcant spectral changes.A time resolved spectral analysis was also performed for the second XMM-Newton observation of V892Tau sys-tem,when the largeﬂare took place.The data were sub-divided into three intervals:aﬁrst14ks interval while the source is quiescent,a second8ks interval while the source counts are rising and the last10ks,while the source is at its luminosity maximum3.The three spec-tra are shown in Fig.6,and their best-ﬁt parameters are listed in Table3.As explained at the beginning of this section an absorbed one-temperature plasma model pro-vides an acceptable description for all the three spectra derived from this exposure,so we did not attemptedﬁts with two-temperature plasma models(which were neces-sary to obtain acceptableﬁts of the spectra derived from theﬁrst XMM-Newton exposure).In addition,the ap-proach toﬂare modelling that we present in Sect.4.2.1 relies on single temperature paramaterization of the X-ray spectrum.Nevertheless,for the spectrum derived from the ﬁrst14ks interval of this exposure(corresponding to the quiescent phase),we veriﬁed that an absorbed two tem-perature plasma model with a metal abundance and two plasma temperatures frozen at the values derived from the ﬁrst XMM-Newton exposure(Z=0.21,kT1=1.02keV and kT2=2.82)indeedﬁts the spectrum(P=0.08).The value for the absorbing column density derived in this way is N(H)=(0.83±0.08)×1022cm−2,somewhat higher than the value derived with the one-temperature plasma ﬁt(N(H)=(0.65±0.06)×1022cm−2,second line of Table3),and in better agreement with the value derived from theﬁrst XMM-Newton exposure.This conﬁrms the lack of signiﬁcant spectral variation in the V892Tau sys-tem during the quiescent phase.As can be seen from Table3,during theﬂare the only signiﬁcant spectral variation occurs in the plasma temper-ature,while theﬁtted values for absorbing column density and plasma metallicity remain essentially unchanged.The plasma temperature increases from kT=1.53keV before theﬂare to kT=8.11during the rising phase and remains around that value afterwards.The model dependentﬂux density of the source,in the energy band0.35–7.50keV, goes from6.7×10−13erg cm−2s−1before theﬂare to 1.0×10−11erg cm−2s−1during theﬂare maximum.The peak X-ray luminosity for theﬂare is L X=2.4×1031erg s−1,high but not exceptionally so for stellar X-rayﬂares.Table2.Theﬁrst four lines of the table report the best-ﬁt spectral parameters for the V892Tau system during the ﬁrst XMM-Newton observation(before theﬂare).The parameters are derived assuming a two-temperature optically thin plasma model.Fits with a single temperature absorbed plasma model are unacceptable in this case.The last line reports the result of a spectralﬁt to the Chandra data on V892Tau with a two-temperature plasma model with the two plasma temperatures and the metal abundance frozen at the values derived from this XMM-Newton exposure (ﬁrst line).See text.Time interval N(H)kT1kT2EM1EM2Zχ2P0–64(total)0.92±0.051.02±0.042.82±0.415.62±2.613.56±1.210.21±0.06 1.070.21 0–300.94±0.100.98±0.10 2.69±0.32 2.65±2.16 4.46±1.090.51±0.200.920.6630–480.89±0.07 1.08±0.09 3.17±1.267.42±4.98 3.03±3.080.13±0.09 1.140.1548–640.98±0.130.77±0.08 1.95±0.17 3.79±2.84 4.43±1.110.31±0.15 1.170.16∗Chandra data(total exposure time)Table3.Best-ﬁt spectral parameters for V892Tau and V892Tau NE during the Chandra observation and the second XMM-Newton exposure.The spectral parameters are derived assuming a single-temperature optically thin plasma model.Source N(H)kT EM Zχ2PV892Tau(Chandra)0.83±0.08 2.10±0.19 4.31±0.950.06±0.07 1.040.40V892Tau(XMM1)0.65±0.06 1.53±0.16 5.19±1.490.09±0.05 1.330.06V892Tau(XMM2)0.97±0.058.11±1.0021.22±1.010.16±0.090.900.79V892Tau(XMM3) 1.00±0.04 6.68±0.5826.44±1.110.26±0.08 1.010.46XMM1:X-ray quiescent,XMM2:rising phase of largeﬂare,XMM3:ﬂare maximumAs already mentioned,V892Tau and V892Tau NE areunresolved by the XMM-Newton PSF,nevertheless the ev-idence that the origin of the observedﬂare is the HerbigAe star is compelling.First,as summarised in Table1,theXMM-Newton position,before and during theﬂare,of thesource associated with system the V892Tau is between2.4and3.1arcsec from the radio position of the main starV892Tau,while is between6and6.8arcsec oﬀthe posi-tion of V892Tau NE.The absolute measurement accuracyof the XMM-Newton pointing is4arcsec(XMM-NewtonUsers’Handbook),so the oﬀset of the source in the EPIC-pn image from the radio coordinates of V892Tau is wellwithin1σof the pointing accuracy.This is fully consistentwith V892Tau being the dominant source of X-ray emis-sion throughout the XMM-Newton observation,as it is thecase during the Chandra observation,where V892Tau isroughly10times more luminous than V892Tau NE.Second,the XMM-Newton position of the source asso-ciated with the system V892Tau before and during theﬂare is constant within0.7arcsec4,while the angular sep-aration of V892Tau and V892Tau NE is4.1arcsec.Atthe same time(as shown in the previous section)the spec-Fig.6.Background-corrected spectra of the V892Tau system during the tree diﬀerent phases of the second XMM-Newton observation.From top to bottom:14ks integration time before theﬂare,8ks during the rising phase of theﬂare,10ks during theﬂare maximum.4.1.Quiescent emissionBy“quiescent”here we mean the time when V892Tau is not undergoing the largeﬂare,even though during this phase we do observe smallerﬂare-like events(both in Chandra and XMM-Newton data).The Chandra spectrum and the XMM-Newton spectra of V892Tau while the source is quiescent can all be well described by an absorbed two temperature plasma model with N(H)∼0.9×1022cm−2kT1=1.0keV,kT2=2.8keV and a relative metal abundance of Z=0.2Z⊙. As discussed above,for the Chandra data a slightly higher value of N(H)is required in order toﬁt the spectrum,con-sistent with the known contamination of the ACIS chips. Here therefore we only refer to the value for N(H)derived from the XMM-Newton data.The X-ray emission from V892Tau has been studied previously by Strom&Strom(1994)and Zinnecker&Preibisch(1994).These two works use the same ROSAT observation but derive from it diﬀerent model parameters.Strom&Strom(1994)ﬁt the spectral data with an absorbed two temperature plasma model with N(H)≃1.3±0.6×1022cm−2,kT1=0.55,kT2=1.20 and estimate an X-ray luminosity L X=1.0×1031erg s−1 (in the0.2–2.4keV band).Zinnecker&Preibisch(1994) model the spectra of V892Tau with an absorbed1temper-ature plasma with N(H)=(4.8±1.1)×1021cm−2,kT=2.3±0.4keV and estimate L X=(1.9±0.8)×1030erg s−1(a factor of≃5lower than the estimate of Strom&Strom 1994).We derive N(H)∼0.9×1022cm−2,compatible to the estimate of Strom&Strom(1994).This value for the absorbing column density corresponds to a visual extinc-tion5of A V∼4.7,which is close to the value estimated by Zinnecker&Preibisch(1994)from the B−V value given in Herbig&Bell(1988)and a factor of∼2lower than derived by Elias(1978)and Strom&Strom(1994)6.We note that a lower value of visual extinction is consistent with the star spectral type being A6rather than B9.The two temperatures for the two component plasma model that we derive here are signiﬁcantly higher than the values given by Strom&Strom(1994);this is not un-expected given the much softer(and narrower)bandpass of the ROSAT PSPC instrument used by Strom&Strom (1994).The temperature derived from our1plasma com-ponentﬁt to the Chandra data(kT=2.1keV)is how-ever consistent with plasma temperature estimated by Zinnecker&Preibisch(1994).The values we derived for the two plasma temperatures in V892Tau are somewhat higher than the typical values derived for the X-ray emis-sion from low mass PMS in Taurus:in an analysis of the spectral characteristic of9T Tauri stars in L1551we found typically kT1∼0.3and kT2∼1.2(Favata et al.2003). On the other hand the value for the plasma metallicity Z=0.2for V892Tau is typical of the value we derived in the same study for the4Weak Lined T Tauri stars in the sample.The intrinsic luminosity we estimate for V892Tau in its quiescent state is L X=1.6×1030erg s−1,in good agreement with the value given by Zinnecker&Preibisch(1994)and a factor of∼6lowerthan derived by Strom&Strom(1994).This indicate that Zinnecker&Preibisch(1994)are probably correct when they suggest that the reason for the discrepancy between their values and the one derived by Strom&Strom(1994) is the fact that Strom&Strom may have erroneously in-cluded the nearby source[BHS98]MHO11in the source circle of V892Tau.A wind-related origin of the X-ray emission has been proposed for Herbig Ae/Be stars by Zinnecker&Preibisch (1994)and Damiani et al.(1994).This scenario,however, seems an unlikely explanation for the origin of the X-ray emission on V892Tau in its quiescent phase.As described in Sect.3,during this phase,V892Tau presents signiﬁcant short term variability,with its X-ray ﬂux varying by a factor of2in less than1ks.The impulsive rise inﬂux appears to be associated with an hardening of the spectrum in the Chandra data.This type of variabil-ity is similar to the one observed in lower-mass pre-main-sequence stars,where the X-ray emission is of coronal ori-gin,while being substantially diﬀerent from the20–30% X-rayﬂux variations observed in OB stars(Collura et al. 1989;Cassinelli et al.1994)where the emission mecha-nism is wind-related.In addition,from the luminosity of V892Tau esti-mated to be around38L⊙(Berrilli et al.1992),its ratio of X-ray luminosity to the total luminosity while quiescent is L X/L bol≃1×10−5.This is two orders of magnitudes greater than the typical ratios found for OB stars.On the other hand a value of L X/L bol≃10−5is not uncommon for low mass stars in which the X-ray emission mechanism is coronal.The possibility of a wind related origin of the X-ray emission from V892Tau in its quiescent phase appears therefore unlikely.This is in agreement with the conclu-sions reached in the two statistical studies of the properties of Herbig Ae/Be stars of Preibisch&Zinnecker(1996)and Hamaguchi et al.(2002a).These studies indicate that the X-ray emission from Herbig Ae/Be stars is generally asso-ciated with higher plasma temperature and higher X-ray to bolometric luminosity ratios than typically observed for the X-ray emission from main sequence OB stars.A wind scenario,ﬁnally,cannot account for the ob-servedﬂare event of V892Tau.4.2.Flare eventDuring theﬂare event the X-ray luminosity of V892Tau increases by a factor of∼15,from L X=1.6×1030erg s−1to L X=2.4×1031erg s−1,while the temperature of the plasma increases from kT=1.5keV to kT=8.1keV. The source luminosity increases over a relatively long time of≃10ks,and hovers close to the luminosity maximum for at least another10ks thereafter–the end of the ob-servation does not unfortunately allow to study the decay phase.As demonstrated by Reale et al.(2002)ﬂares of this type cannot take place in the freely expanding plas-moids of a stellar wind.The observed slow increase of X-ray luminosity at the beginning of theﬂare event requires the presence of a conﬁning magneticﬁeld.In order to gain some quantitative insight on the event and given the similarities of the derived light curve with the ones of other stellarﬂares we have analyzed the event through scaling obtained from detailed hydrody-namic models ofﬂaring plasma conﬁned in a closed coronal loops,as in solarﬂares.4.2.1.Flaring region characteristicsIt is customary to derive information about the size of the ﬂaring loops from theﬂare evolution,i.e.the light curve. It has been shown that the decay time of the light curve is linked to the plasma cooling times,which,in turn,depends on the length of the loop which conﬁnes the plasma(e.g. Reale2002and references therein):the slower the decay, the longer the loop,unless a signiﬁcant residual heating sustains the decay and makes the decay-time/cooling-time dependence less tight.The XMM-Newton observation of theﬂare on V892 Tau does not cover the decay phase and therefore diag-nostics using the characteristics decay times are not feasi-ble.For this particularﬂare,however,we are able to infer some information on the size of theﬂaring region from the observed rise phase.The evolution of theﬂaring plasma conﬁned in a loop is well-known from extensive hydrodynamic loop model-ing(e.g.Peres et al.1982):a strong heating pulse is trig-gered in an initially quiescent coronal loop and makes the temperature increase by up to several tens of MK along the whole loop in a few seconds,due to the high plasma thermal conduction.The dense chromosphere at the loop footpoints is heated violently and expands upwards with a strong evaporation front.The rising plasmaﬁlls up the loop,very dynamicallyﬁrst and then more gradually,ap-proaching a new hydrostatic equilibrium at a very high pressure.The loop X-ray emission increases mostly fol-lowing the increase of emission measure,and forms the rise phase of theﬂare.Although the evolution in the rise phase is very dy-namic and non-linear,we can nevertheless derive an ap-proximate time scaling.From the equation of energy con-servation of the conﬁned plasma(e.g.Eq.(3)in Serio et al. 1991)it can be seen that,after the very initial seconds, dominated by the plasma kinetics,the evolution in the bulk of the rise phase can be approximately described as a linear increase of the plasma internal energy density driven by the(constant)energy input rate per unit volume:dǫ。

Observations of Pulsar Wind Nebulae with the VERITAS Array of Imaging Atmospheric Cherenkov

a r X i v :0709.3975v 1 [a s t r o -p h ] 25 S e p 200730TH I NTERNATIONAL C OSMIC R AY C ONFERENCEObservations of Pulsar Wind Nebulae with the VERITAS Array of Imaging Atmo-spheric Cherenkov Telescopes A.K ONOPELKO 1,FOR THE VERITAS COLLABORATION 21Purdue University,Department of Physics,525Northwestern Avenue,West Lafayette,IN 47907-2036,2For full author list see G.Maier,”VERITAS:Status and Latest Results”,these proceedings akonopel@ Abstract:Many of the recently discovered galactic very high-energy (VHE)γ-ray sources are associated with Pulsar Wind Nebulae,which is the most populous Galactic source category at TeV energies.The extended synchrotron nebulae of these objects observed in the X-ray band are a hallmark of the relativis-tic winds,generated by the young,energetic neutron stars,that interact with the matter ejected by the supernova explosion and the surrounding interstellar gas.Relativistic electrons,or protons,accelerated in the pulsar winds,or at their shock boundaries,interact with the magnetic ﬁeld and low energy seed photons to produce the observed VHE γ-ray emission.The VERITAS array of four imaging atmospheric Cherenkov telescopes was designed to study astrophysical sources of γrays in the energy domain from about 100GeV up to several tens of TeV .The sensitivity of the VERITAS array allows detailed stud-ies of the morphology and spectral features of γ-ray emission from PWNe.Three northern sky PWNe,G75.2+0.1,G106.6+2.9,and 3C58,were observed with VERITAS during 2006.No evidence for TeV γ-ray emission at the position of the pulsar associated with these PWNe is demonstrated.Introduction Charged particles accelerated in the vicinity of a rapidly rotating neutron star,or pulsar,ﬂow out into the interstellar medium and encounter the su-pernova ejecta from the pulsar’s birth event and form a shock.The shock may further enhance the acceleration of the particles which can then attain relativistic speeds.This interaction between the accelerated charged particles and the surrounding medium produces a pulsar wind nebula (PWN).PWNe are often observable at wavelengths fromthe radio through the γ-ray.Around the youngest,most energetic pulsars,the radio emitting regionsof these nebulae are rather amorphous,whereasthe X-ray emitting regions can be highly structured[10].The high spatial resolution of the ChandraX-ray Observatory has made it possible to resolvethe structures of PWNe.The presence of a PWNcan also be inferred spectrally.For instance,anon-thermal component is often seen in the ASCAand INTEGRAL observations of pulsars,such asPSR B1509-58and PSR B1046-58.This seems tosuggest that PWNe are a common phenomenon forall energetic pulsars [14].It was widely believed that PWNe are potential sources of VHE γ-ray emission.The emission probably arises from inverse Compton (IC)scatter-ing of low-energy photons by the relativistic elec-trons,while the X-ray emission is associated with the synchrotron radiation from the same popula-tion of electrons.The best example of a PWN is the Crab Nebula,which is an established source of pulsed γ-ray emission up to a few GeV detected by EGRET,as well as a source of steady TeV γrays observed by a number of ground-based Cherenkov detectors and recently with the VERITAS array of four imaging atmospheric Cherenkov telescopes [4].The TeV emission is thought to originate at the base of its PWN.The H.E.S.S.detector,located in the southern hemisphere,discovered a number of previously unknown γ-ray sources in the VHE do-main above 100GeV .A total of ﬁve of these new sources (PSR B1509-58,Vela X,“Kookaburra”,SNR G0.9+0.1,PSR B1823-13)are apparently as-sociated with PWNe.Such associations rest on a positional and morphological match of the VHE γ-ray source to a known PWN at lower energies.It is worth noting that in all cases the pulsar is sig-O BSERVATIONS OF PWN E WITH VERITASPulsarJ2021+3651G106.6+2.951.6210.52234 J0205+6449Table1:Physical parameters of observed pulsars and their PWNe.niﬁcantly offset from the center of the VHEγ-ray source.This offset could be attributed to the inter-action between the PWN and the SNR ejecta[3].A detailed survey of the inner part of the Galac-tic Plane at VHEγ-ray energies has been carried out with H.E.S.S.Fourteen previously unknown, extended sources were detected with high signif-icance[7].Some of these sources have fairly well-established counterparts at longer wavelengths, based exclusively on positional coincidence,but others have none at all.A number of mod-els have been proposed regarding the nature of these unidentiﬁed VHEγ-ray sources.At present, PWNe and shell-type SNRs are considered the most plausible counterparts for the remaining unidentiﬁed VHEγ-ray sources amongst the nu-merous possibilities that have been put forward. TargetsMotivated by the growing catalog of TeV PWNe, VERITAS,in2006,observed three northern sky PWNe,G75.2+0.1,G106.6+2.9,and3C58,asso-ciated with young,energetic pulsars(see Table1). PSR J2021+3651.A Chandra observation showed this pulsar to be embedded in a compact,bright X-ray PWN(PWN G75.2+0.1)with the standard torus and jet morphology[13].Its X-ray spectrum is wellﬁt by a power-law model with photon in-dexΓ=1.7and a corresponding0.3-10keVﬂux of1.9×10−12erg cm−2s−1.This young Vela-like pulsar is coincident with the EGRETγ-ray source GeV2020+3651.Recently,the Milagroγ-ray ob-servatory detected an extended source or multiple unresolved sources ofγrays at a median-detected energy of12TeV[8]coincident with the same re-gion.The radio dispersion measure suggests a dis-tance to PWN G75.2+0.1d≥10kpc,but this measurement could have been contaminated by the gas in the Cygnus region and the true distance may be in fact substantially closer.Presently PWN G75.2+0.1is considered to be one of the best can-didates for the Milagro source(MGRO J2021+37)and it is likely to be seen in the energy range cov-ered by VERITAS.PSR J2229+6114.The Chandra X-ray image of PWN G106.6+2.9shows an incomplete elliptical arc and a possible jet,similar to the Vela PWN [11].PSR J2229+6114is a compelling counter-part of the EGRET source3EG J2227+6122.This young,energetic pulsar is second only to the Crab pulsar in spin-down power,and it is substantially more luminous than the Vela pulsar.Given the rel-atively small distance of3kpc this pulsar has a very high rank among all pulsars in the discrimi-nant˙E/d2.Part of thisﬂux can be converted into a highﬂux of VHEγrays.3C58.3C58is a young Crab-like SNR generally accepted as being the remnant of the historical su-pernova SN1181.A compact object(nebula)at the center of the SNR has been resolved in Chandra X-ray data[16],and is centered on PSR J0205+6449. Given its very high spin-down power,the pulsar is capable of supplying the energy of the X-ray neb-ula,L x=2.9×1034ergs s−1,and may have sub-stantial VHEγ-ray emission.The TeVγ-rayﬂuxes expected from the PWNe around both PSR J2021+3651and PSR J2229+6114in terms of a hadronic-leptonic model for the high-energy processes inside the PWNe[2]exceed10%of the Crab Nebulaﬂux above200GeV(see Table1).This suggests that both PSR J2021+3651and PSR J2229+6114 should be detectable with VERITAS after rather short exposures.A somewhat lowerγ-rayﬂux of a few percent of the Crab Nebula was predicted for3C58[2],however it is still well above the sensitivity limit of the VERITAS detector for a reasonable exposure.VERITAS Observations and Analysis VERITAS is an array of four imaging Cherenkov telescopes sited in Amado,Arizona,and dedicated to the detection of VHEγrays with energies above 100GeV.Each telescope has a tessellated mirror30TH I NTERNATIONAL C OSMIC R AY C ONFERENCEPulsar N tel N runs R(Hz)T(hr)Θ(◦)On OffαLi&Ma S/N(σ)U.L.(Crab)Table2:Summary of data.with an area of≃110m2and a camera consisting of499photomultiplier tubes.Theﬁrst telescope in the array has been operating since February2005. First stereo observations with two telescopes began in April2006,and the full array of four telescopes has been operational since January2007.A full VERITAS array has the sensitivity of7mCrab(5σdetection over50hour exposure).The angular res-olution of better than0.14◦and a3.5◦ﬁeld of view enable VERITAS to detect and study a variety of compact galacticγ-ray sources like PWNe.The VERITAS observations of three PWNe were made while the system was under construc-tion.Observations of PSR J2021+3651and PSR J2229+6114in November2006were made with a two telescope ter a third tele-scope was added to the system and observa-tions of3C58in December2006were made with three telescopes.The data were taken mostly in 20minute runs with a few runs of28minutes using the wobble mode.In this mode,the source direc-tion is positioned±0.3◦(a±0.5◦offset was used for later observations)in declination or right as-cension relative to the center of the cameraﬁeld of view.The sign of the offset was altered in succes-sive runs to reduce systematic effects.The wob-ble mode allows on-source observation and simul-taneous estimation of the background induced by charge cosmic-ray particles.This eliminates the need for off-source observations and consequently doubles the amount of available on-source time. Forﬁnal analysis only those runs passing the data quality criteria are used.The images are cali-brated and then cleaned using a two-threshold pic-ture/boundary selection procedure which requires a pixel to have a signal greater than5.0pedestal variances(PV)and a neighboring pixel to have a signal larger than2.5PV.The pixels with a sig-nal greater than2.5PV are included only if they have a neighbor with a signal greater than5.0PV. After image cleaning the shower images are pa-rameterized using a standard second-moment ap-proach.The shower geometry is reconstructed us-ing stereoscopic techniques with a typical angu-lar resolution of about0.14◦and an average accu-racy of better than20m in the determination of the shower core location.To ensure that images are not truncated by the camera edge,only images with the center of gravity less than1.3◦from the center of the camera are used in the reconstruction.In ad-dition,at least two images are each required to ex-ceed a minimum total signal of400digital counts of the respectiveﬂash analog-to-digital converter to ensure that the showers are well reconstructed. After the shower reconstruction,the cosmic-ray background events are rejected using standard cuts on mean scaled width and mean scaled length parameters.The number of events passing cuts in a circle of standard angular size around the source position gives the number of on-source(On) counts.The background is estimated using all events passing cuts in a number of non-overlapping circles of the same size.The centers of these cir-cles are positioned at the wobble offset from the tracking position.The number of background re-gions may vary depending on the actual wobble offset used in the observation.The use of a larger background region reduces the relative statistical error on the background measurement.For a given number of on-source and background counts ac-quired after event selection the signiﬁcance of the excess is calculated following the method of Equa-tion(17)in the Li&Ma technique[15].It is worth noting that the data have been analyzed using in-dependent analysis packages(see[5,9]for details on the analyses).All of these analyses yield con-sistent results.Results and ConclusionTable2summarizes the results of the VERITAS observations of each of the individual sources. These objects have been observed with VERITAS for rather limited exposure times.The longest ex-posure(T)of12hrs was for PSR J2229+6114.All observations were made at the median zenith an-O BSERVATIONS OF PWN E WITH VERITAS。

法布里珀罗基模共振英文

法布里珀罗基模共振英文The Fabryperot ResonanceOptics, the study of light and its properties, has been a subject of fascination for scientists and researchers for centuries. One of the fundamental phenomena in optics is the Fabry-Perot resonance, named after the French physicists Charles Fabry and Alfred Perot, who first described it in the late 19th century. This resonance effect has numerous applications in various fields, ranging from telecommunications to quantum physics, and its understanding is crucial in the development of advanced optical technologies.The Fabry-Perot resonance occurs when light is reflected multiple times between two parallel, partially reflective surfaces, known as mirrors. This creates a standing wave pattern within the cavity formed by the mirrors, where the light waves interfere constructively and destructively to produce a series of sharp peaks and valleys in the transmitted and reflected light intensity. The specific wavelengths at which the constructive interference occurs are known as the resonant wavelengths of the Fabry-Perot cavity.The resonant wavelengths of a Fabry-Perot cavity are determined bythe distance between the mirrors, the refractive index of the material within the cavity, and the wavelength of the incident light. When the optical path length, which is the product of the refractive index and the physical distance between the mirrors, is an integer multiple of the wavelength of the incident light, the light waves interfere constructively, resulting in a high-intensity transmission through the cavity. Conversely, when the optical path length is not an integer multiple of the wavelength, the light waves interfere destructively, leading to a low-intensity transmission.The sharpness of the resonant peaks in a Fabry-Perot cavity is determined by the reflectivity of the mirrors. Highly reflective mirrors result in a higher finesse, which is a measure of the ratio of the spacing between the resonant peaks to their width. This high finesse allows for the creation of narrow-linewidth, high-resolution optical filters and laser cavities, which are essential components in various optical systems.One of the key applications of the Fabry-Perot resonance is in the field of optical telecommunications. Fiber-optic communication systems often utilize Fabry-Perot filters to select specific wavelength channels for data transmission, enabling the efficient use of the available bandwidth in fiber-optic networks. These filters can be tuned by adjusting the mirror separation or the refractive index of the cavity, allowing for dynamic wavelength selection andreconfiguration of the communication system.Another important application of the Fabry-Perot resonance is in the field of laser technology. Fabry-Perot cavities are commonly used as the optical resonator in various types of lasers, providing the necessary feedback to sustain the lasing process. The high finesse of the Fabry-Perot cavity allows for the generation of highly monochromatic and coherent light, which is crucial for applications such as spectroscopy, interferometry, and precision metrology.In the realm of quantum physics, the Fabry-Perot resonance plays a crucial role in the study of cavity quantum electrodynamics (cQED). In cQED, atoms or other quantum systems are placed inside a Fabry-Perot cavity, where the strong interaction between the atoms and the confined electromagnetic field can lead to the observation of fascinating quantum phenomena, such as the Purcell effect, vacuum Rabi oscillations, and the generation of nonclassical states of light.Furthermore, the Fabry-Perot resonance has found applications in the field of optical sensing, where it is used to detect small changes in physical parameters, such as displacement, pressure, or temperature. The high sensitivity and stability of Fabry-Perot interferometers make them valuable tools in various sensing and measurement applications, ranging from seismic monitoring to the detection of gravitational waves.The Fabry-Perot resonance is a fundamental concept in optics that has enabled the development of numerous advanced optical technologies. Its versatility and importance in various fields of science and engineering have made it a subject of continuous research and innovation. As the field of optics continues to advance, the Fabry-Perot resonance will undoubtedly play an increasingly crucial role in shaping the future of optical systems and applications.。

入侵植物喜旱莲子草_生物学_生态学及管理_潘晓云

植物分类学报 45 (6): 884–900(2007)doi:10.1360/aps06134 Acta Phytotaxonomica Sinica ———————————2006-08-28收稿, 2007-03-12收修改稿。

基金项目: 国家自然科学基金(30400052); 国家重点基础研究发展计划资助(2006CB403305) (Supported by the National Natural Science Foundation of China, Grant No. 30400052; National Basic Research Program of China, Grant No. 2006CB403305 )。

* 通讯作者(Author for correspondence. E-mail: jkchen@; Tel.: 86-21-65642468; Fax: 86-21-65642468)。

入侵植物喜旱莲子草——生物学、生态学及管理1潘晓云 1耿宇鹏 2Alejandro SOSA 1张文驹 1李博 1陈家宽*1(生物多样性和生态工程教育部重点实验室, 复旦大学生物多样性科学研究所, 长江河口湿地生态系统野外科学观测研究站上海 200433)2(南美生物防治实验室布宜诺斯艾利斯 1686)Invasive Alternanthera philoxeroides : biology, ecology andmanagement1PAN Xiao-Yun 1GENG Yu-Peng 2Alejandro SOSA 1ZHANG Wen-Ju 1LI Bo 1CHEN Jia-Kuan * 1(Ministry of Education Key Laboratory for Biodiversity Science & Ecological Engineering , Institute of Biodiversity Science ,Fudan University , Coastal Ecosystems Research Station of Yangtze River Estuary , Shanghai 200433, China) 2(South American Biological Control Laboratory , USDA-ARS , Hurlingham-Buenos Aires 1686, Argentina) Abstract In this review, we present a detailed account of Alternanthera philoxeroides (alligatorweed), including A. philoxeroides description, intraspecific variation from native to introduced regions, its life history strategies, invasion mechanisms, and management strategies. Alternanthera philoxeroides is a herbaceous amphibious weed of Amaranthaceae, native to South America, distributed from Buenos Aires Province (39° S) to south Brazil. It was first described by Martius in 1826, and consists of several taxa in both its native and non-native ranges. Current knowledge indicates that two forms of alligator weed exist in Argentina: A. philoxeroides f. philoxeroides in the southern range and A. philoxeroides f. angustifolia in the northern range. In Argentina, both forms set fruits and produce viable seeds. Alternanthera philoxeroides is now found as a serious weed from tropical to warm temperate regions, including the USA, China, India, South-East Asia, Australia and New Zealand. It is thought to have been brought to China during the 1930s, and later widely cultivated and spread in southern China as fodder during 1950s. The invasions of alligatorweed in China have caused considerable concerns, and now it is one of the 12 most harmful alien invasive species in China. Alligatorweed is found on stationary and slow moving water bodies, creeks, channels, riverbanks and associated areas that are occasionally flooded. It can also be found in terrestrial habitats as a pasture weed within urban environments. Alligatorweed does not produce viable seed in China and reproduces vegetatively from vegetative fragments (stems, rhizome or root tubes), which can be transported by water movement, boats, machinery and vehicles, and in hay. Movement between river catchments is common because of the human activities. Alligatorweed forms a floating mass which spreads out over the water. Its growth disrupts the ecology of banks and shallows and crowds out other plant species, restricts water flow, increases sedimentation, aggravates flooding, limits access and use by man and provides a favorable breeding area for disease vectors. We need better understanding of the biology and ecology of alligatorweed to assess the efficiency of control methods in any theoretical framework. According to the6期潘晓云等: 入侵植物喜旱莲子草——生物学、生态学及管理885 knowledge of the life history strategy of alligatorweed, we suggest that metapopulation theory is a good tool to improve management efficiency from watershed and regional perspectives. Key words alligatorweed (Alternanthera philoxeroides), biological invasion, dispersal, disturbance, intraspecific variation, life history, metapopulation, watershed management.摘要喜旱莲子草Alternanthera philoxeroides原产于南美洲, 属于苋科Amaranthaceae莲子草属Alternanthera。

SuperWASP Observations of the Transiting Extrasolar planet XO-1b

a r X i v :a s t r o -p h /0607591v 1 26 J u l 2006SuperW ASP Observations of the Transiting Extrasolar planetXO-1bD.M.Wilson 1,B.Enoch 2,D.J.Christian 3,W.I.Clarkson 2,4,A.Collier Cameron 5,H.J.Deeg 6,A.Evans 1,C.A.Haswell 2,C.Hellier 1,S.T.Hodgkin 7,K.Horne 5,J.Irwin 7,S.R.Kane 5,8,T.A.Lister 5,1,P.F.L.Maxted 1,A.J.Norton 2,D.Pollacco 3,I.Skillen 9,R.A.Street 3,R.G.West 10,P.J.Wheatley 11ABSTRACT We report on observations of 11transit events of the transiting extrasolar planet XO-1b by the SuperWASP-North observatory.From our data,obtained during May-September 2004,we ﬁnd that the XO-1b orbital period is 3.941634±0.000137days,the planetary radius is 1.34±0.12R Jup and the inclination is 88.92±1.04◦,in good agreement with previously published values.We tabulate the transit timings from 2004SuperWASP and XO data,which are the earliest obtained for XO-1b,and which will therefore be useful for future investigations of timing variations caused by additional perturbing planets.We also present an ephemeris for the transits.Subject headings:Stars:planetary systems1http://exoplanet.eu/2Southern hemispheres.SuperWASP-North (SW-N)is based on La Palma,Canary Islands,andSuperWASP-South (SW-S)is based at SAAO,South Africa.Both observatories consist of 8cam-eras,each with an 11.1cm aperture Canon 200mm f/1.8lens backed by a 2k ×2k EEV CCD.Each camera has a ﬁeld of view of 7.8×7.8degrees with a 13.7′′/pix plate scale,resulting in a total ﬁeld of view of almost 500square degrees per observatory.Further details of the project are given in Pollacco et al.(2006).The SW-N observatory obtained nearly 4500in-dividual observations of XO-1over 150days be-tween 2May 2004to 29September 2004.The object was recorded by two cameras producing a total of 8875measurements.The photometric pre-cision,when outliers from cloudy nights are ex-cluded,is approximately 9mmags (RMS).This is slightly worse than usual for stars of this magni-tude owing to the close proximity to the edges of the camera ﬁelds.Lightcurves from SuperWASP are de-trendedusing the algorithm of Tamuz et al.(2005)beforebeing passed through hunter (Collier Cameronet al.2006),a transit search algorithm based onthe method of Protopapas et al.(2005).The algorithm computes χ2values of transit modellightcurves using a box-shaped model slid overthe observed lightcurve.Typically,a few tensof transit-like lightcurves are identiﬁed from each CCD ﬁeld of 10-20,000objects.The hunter output for XO-1(1SWASP J160211.83+281010.4)is shown in Figure 1.The periodogram showsthe value of χ2for the best least-squares ﬁt ateach frequency;the de-trended lightcurve is phase-folded on the best ﬁtting period of 3.942134days.hunter listed this object as a high priority can-didate to be considered for further investigation.3.Lightcurve FittingThe SW-N data covers 11transit events and,excluding outliers,consists of 8468datapoints.The transits were ﬁtted to a simulated planetary transit generated using ebop (Eclipsing Binary Orbit Program;Popper &Etzel (1981)).ebop uses biaxial ellipsoids to simulate eclipsing binary star systems;however,by considering the sec-ondary as an opaque disc,a transiting planetarysystem can easily be modelled.The simulatedlightcurve is dependent upon the radii ratio of thetransiting planet to the parent star R pl /R ⋆,the inclination of the transiting planet’s orbit,i p ,and the limb-darkening coeﬃcient of the star.The limb-darkening coeﬃcient was determined by convolving the SuperWASP bandpass with ﬂuxes and monochromatic coeﬃcients listed by Van Hamme (1993).A linear limb-darkening co-eﬃcient of 0.565was calculated for the stellar tem-perature of 5750K (G1V)quoted by McCullough et al.(2006).The best-ﬁt parameters determined from a least-squares ﬁt to all transits simultaneously are listed in Table 1.Figure 2shows the data phase-folded on the best-ﬁtting period with the best-ﬁt model overplotted.The original XO survey data (Peter McCullough,private communication),ob-tained on a similar instrument to SW-N,are also shown for comparison.The errors were generated using a boot-strap Monte Carlo method in which we generated and re-ﬁt 1000simulated data setsfrom the best-ﬁt lightcurve with the same sam-pling and noise characteristics as the observed lightcurve.The planetary radius was determined from the ratio R pl /R ⋆by using the stellar radius of 1.0±0.08R ⊙determined spectroscopically by McCullough et al.(2006).The parameters deter-mined from the ﬁt are consistent with previously published values (McCullough et al.2006).11transit events were identiﬁed from the de-termined period and ephemeris and the best-ﬁtmodel was ﬁtted to each of these individually to determine the time of mid-transit T 0(Table 2).The best ﬁt model was also ﬁtted to the XO survey data which cover 3transit events and were also ob-tained in 2004.Three of the total fourteen transits were rejected either due to insuﬃcient coverage of the transit event,or in one case the data being too noisy to produce an adequate ﬁt.The errors weregenerated by perturbing T 0so as to increase χ2by one and are typically of the order 5-10mins,which is comparable to the data sampling rate.This paper has demonstrated that SuperWASP can detect and characterise exoplanet transits and obtain suﬃcient data to determine an ephemeris.Other candidate exoplanet transits from our 2004data will be reported in subsequent papers.4.AcknowledgementsThe WASP consortium consists of representa-tives from the Universities of Cambridge(Wide Field Astronomy Unit),Keele,Leicester,The Open University,Queen’s University Belfast and St Andrews,along with the Isaac Newton Group (La Palma)and the Instituto de Astrophysic de Canarias(Tenerife).The SuperWASP-N and SuperWASP-S Cameras were constructed and op-erated with funds made available from Consortium Universities and PPARC.We are grateful to the XO team for making available the original XO photometry. REFERENCESCollier Cameron,A.et al.,2006,MNRAS,Sub-mittedMcCullough,P.R.,et al.,2006,ApJ,In-Press Pollacco,D.,et al.,2006,PASP,Submitted Popper,D.M.,Etzel,P.B.,1981,AJ,86,102 Protopapas,P.,Jimenez,R.,Alcock,C.,2005, MNRAS,362,460Tamuz,O.,Mazeh,T.,Zucker,S.,2005,MNRAS, 356,1466Van Hamme,W.,1993,AJ,106,2096Table1:Bestﬁtting parameters of XO-1from the ﬁt of the SW-N data.Parameter SW-Na From McCullough et al.(2006)Table2:Best-ﬁt times of mid-transit for full and partial XO-1b transits from SW-N and XO survey data.Observatory HJD(mid-transit)Transit N XO2453123(no-ﬁt)bXO2453127.0385±0.0058(partial)32 XO2453142.7818±0.0218(partial)40 SW-N2453146(no-ﬁt)bSW-N2453150.6855±0.0106(partial)88 SW-N2453154.6250±0.0026(full)99 SW-N2453158.5663±0.0034(full)102 SW-N2453162.5137±0.0025(full)117 SW-N2453166.4505±0.0025(partial)68 SW-N2453170.3917±0.0037(partial)65 SW-N2453229.5143±0.0045(partial)54 SW-N2453233(no-ﬁt)bSW-N2453237.4043±0.0032(partial)47 SW-N2453241.3410±0.0067(partial)38Fig. 1.—Hunter output for object 1SWASPJ160211.83+281010.4(camera2)in-cluding periodogram and lightcurve folded on the Hunter determined best-ﬁtting period of3.942134 days.Fig. 2.—SuperWASP-North data(upper panel) and XO survey data(lower panel)for XO-1phase folded on the bestﬁtting parameters listed in Ta-ble1with the best-ﬁt model over-plotted.。

and

G. V. Jung
Accepted for publication in the Astrophysical Journal
ABSTRACT
The Oriented Scintillation Spectrometer Experiment on the Compton Gamma Ray Observatory observed the Galactic black hole candidate GX 339?4 as a target of opportunity in 1991 September, in response to the outburst reported by BATSE. We report here on energy spectra in the 50 keV to 10 MeV range obtained by OSSE. The source was detected from 50 to 400 keV at a level relative to the Crab nebula of 30%. The observed spectrum was described reasonably well by a power law with an exponential cuto ; a least-squares t yielded a photon index of :88 :05 and a cuto energy of (68 2) keV. The addition of a Compton re ection component did not signi cantly improve the overall t. An optically-thin thermal bremsstrahlung spectrum also provides a good t, and the thermal Comptonization model of Sunyaev and Titarchuk, while de cient in describing the data above about 200 keV, cannot formally be ruled out. A pure power law with re ection does not t the observed spectrum. During a follow-up observation made in 1991 November, the intensity of the source below 100 keV

浅谈松材线虫病的危害及防治措施

文章编号：1673-887X(2023)04-0114-03浅谈松材线虫病的危害及防治措施甘小芳（贵港市覃塘林场，广西壮族自治区贵港537100）摘要松材线虫病是危害松树林带的重要病害，防治不当对松树林带将会造成毁灭性打击，阻碍林业经济发展，影响森林生态。

文章以松材线虫病的危害为切入点，简单阐述松材线虫病存在感染速度快、致死率高、检测难度大的危害因素，以此为基础，结合松材线虫病的监测方案，提出物理防治、化学防治、生物防治、营林防治的四种防治措施，从而为相关工作者提供参考。

关键词松树；松材线虫病；危害；防治措施中图分类号S436文献标志码Adoi:10.3969/j.issn.1673-887X.2023.04.043Discussion on the Harm and Prevention Measures of Bursaphelenchusxylophilus (SteineretBuhrer)Gan Xiaofang(Qintang Forest Farm of Guigang City,Guigang 537100,Guangxi Zhuang Autonomous Region,China)Abstract ：Bursaphelenchusxylophilus (SteineretBuhrer)is an important disease that endangers the pine forest belt.Improper preven ‐tion and control will cause a devastating blow to the pine forest belt,hinder the development of forestry economy and affect the for ‐est ecology.This paper took the harm of Bursaphelenchusxylophilus (SteineretBuhrer)as the starting point,and briefly expounded the harm of Bursaphelenchusxylophilus (SteineretBuhrer)that has fast infection rate,high mortality rate and great difficulty in detec ‐tion.On this basis,combined with the monitoring plan of Bursaphelenchusxylophilus (SteineretBuhrer),this paper put forward four prevention and control measures of physical control,chemical control,biological control and forest management,so as to provide ref ‐erence for relevant workers.Key words ：pine,Bursaphelenchusxylophilus (SteineretBuhrer),harm,prevention and control measures松材线虫病也称为松树萎蔫病，是线虫感染引发的侵染性系统病害。

bias dependent cluster centroid shi

•Charge collection efficiency studies with irradiated silicon detectors. (Allport et al.)
NIM A 501 (2003) 146-152
Similar results, the ballistic deficit at 100 V is
position. – Observation of possible ballistic deficit in VELO. – Anomalous centroid shifts.
Aras Papadelis. NIKHEF. Nov 9. 2005, Vertex 2005
2/16
The sensors in the VELO detector
to cause misalignment
Aras Papadelis. NIKHEF. Nov 9. 2005, Vertex 2005
300 µm 10/16
Ballistic deficit?
R300 R200
R200
• Signal increases between 100V and 300V. • Is this ballistic deficit?
Cluster centroid shift n+
– no charge trapping (unirradiated) – homegenous E-field – same µ everywhere in sensor. ● Electrons in the grey region do not contribute fully to the signal.
● Sept 2004: Steve Biagi (LHCb Liverpool) suggests that ballistic deficit in non-irradiated sensors can give offsets in reconstructed cluster position for angled tracks.

a-group-of-researchers-studying-the-behaviour

a group of researchers studying the behaviourof a particular species of birds. They are interested in understanding their mating patterns and social dynamics. The researchers observe the birds in their natural habitat and collect data on various aspects of their behavior.To study the mating patterns, the researchers observe the courtship rituals of the birds. They note down the behaviors displayed by males and females during courtship, such as singing, dancing, and displaying colorful feathers. They also record the duration of courtship and the number of successful mating pairs.The researchers also study the social dynamics within the bird group. They observe interactions between individuals, such as aggression, cooperation, and territorial disputes. They note down the individuals involved in these interactions and the outcome of each interaction.To collect data, the researchers spend hours observing the birds using binoculars and cameras. They also set up video cameras and audio recorders to capture the birds' behaviors. They carefully document their observations in field notebooks and record any important details.In addition to direct observations, the researchers may also use other methods to study the birds' behavior. For example, they may capture and tag some individuals to track their movements and interactions. They may also collect feathers or droppings for genetic analysis to understand the relatedness between individuals in the group.Once the data is collected, the researchers analyze it to identify patterns and trends in the birds' behavior. They may use statistical methods to determine if there are any significant differences in courtship behavior or social interactions between different individuals or groups within the bird population.The researchers may also compare their findings with existing literature on the species to see if their observations align with previous studies orif they have discovered any new behaviors or patterns.Overall, studying the behavior of a particular species of birds involves careful observation, data collection, and analysis to gain insights intotheir mating patterns and social dynamics. This research can contribute to our understanding of the species and help in conservation efforts.。

苦参汤坐浴加内括约肌松解术对嵌顿痔的治疗效果评价

中医中药China &Foreign Medical Treatment 中外医疗苦参汤坐浴加内括约肌松解术对嵌顿痔的治疗效果评价沈文清，林国强，沈鸿堂莆田市荔城区医院，福建莆田 351144［摘要］目的探索嵌顿痔患者接受苦参汤坐浴联合内括约肌松解术的临床价值。

方法随机选择2021年5月—2023年5月莆田市荔城区医院接治的80例嵌顿痔患者为研究对象，通过随机抽签法作分为对照组与观察组，各40例。

对照组采用高锰酸钾溶液坐浴联合内括约肌松解术治疗，观察组以苦参汤坐浴联合内括约肌松解术治疗。

比较两组临床总疗效、临床指标时间、术后不同时间点疼痛程度以及相关并发症发生情况。

结果观察组临床总有效率为95.00%高于对照组的75.00%，差异有统计学意义（χ2=6.274，P =0.012）。

观察组水肿回纳时间、创面愈合时间、总住院时间均短于对照组，差异有统计学意义（P <0.05）。

术后1 d 、术后3 d 以及出院时，观察组视觉模拟评分法（Visual Analogue Scale, VAS ）评分均明显比对照组低，差异有统计学意义（P <0.05）。

观察组并发症发生率比对照组低，差异有统计学意义（P <0.05）。

结论嵌顿痔患者在接受内括约肌松解术治疗的基础上采取苦参汤坐浴可促进临床疗效进一步提升，缩短临床康复时间，缓解术后疼痛程度，降低术后并发症发生率。

［关键词］嵌顿痔；苦参汤坐浴；内括约肌松解术；临床疗效［中图分类号］ R5 ［文献标识码］ A ［文章编号］ 1674-0742（2023）10(b)-0195-04Evaluation of the Therapeutic Effect of Kushen Decoction and Internal Sphincter Relaxation on Incarcerated HemorrhoidsSHEN Wenqing, LIN Guoqiang, SHEN HongtangPutian Licheng District Hospital, Putian, Fujian Province, 351144 China[Abstract] Objective To explore the clinical value of Kushen decoction and internal sphincter relaxation in patients with incarcerated hemorrhoids. Methods 80 cases of incarcerated hemorrhoids treated in Licheng District Hospital of Putian City from May 2021 to May 2023 were randomly selected as the study objects, and were divided into control group and observation group by random drawing method, with 40 cases in each group. The control group was treated with potassium permanganate solution sitz bath combined with internal sphincter release, and the observation group was treated with Kushen decoction sitz bath combined with internal sphincter release. The total clinical efficacy, clini⁃cal index time, postoperative pain degree at different time points and the occurrence of related complications werecompared between the two groups. Results The total clinical effective rate of observation group was 95.00%, which was higher than that of control group 75.00%, and the difference was statistically significant (χ2=6.274, P =0.012). The retention time of edema, wound healing time and total hospital stay in the observation group were shorter than those inthe control group, and the difference was statistically significant (P <0.05). The Visual Analogue Scale (VAS) score of the observation group was significantly lower than that of the control group on the 1st and 3rd d after surgery and at the time of discharge, and the difference was statistically significant (P <0.05). The incidence of complications in the observation group was lower than that in the control group, and the difference was statistically significant (P <0.05). Conclusion Kushen decoction sitz bath on the basis of internal sphincterolysis treatment for incarcerated hemorrhoidscan further improve the clinical effect, shorten the clinical rehabilitation time, relieve postoperative pain and reduceDOI ：10.16662/ki.1674-0742.2023.29.195[作者简介] 沈文清（1981-），男，本科，主治中医师，研究方向为中医肛肠相关。

Mammalian Saliva Sample

Mammalian Saliva SampleMammalian saliva samples are an important aspect of biological research, as they can provide valuable insights into various aspects of an organism's health, behavior, and evolution. Saliva contains a complex mixture of proteins, enzymes, hormones, and other molecules that can offer a wealth of information to researchers. From a scientific perspective, studying mammalian saliva samples can help us better understand the mechanisms of digestion, the immune system, and even the spread of diseases. One of the key reasons why mammalian saliva samples areof interest to researchers is their potential as a non-invasive method ofobtaining biological information. Unlike blood or tissue samples, collectingsaliva is relatively easy and painless, making it an attractive option forstudying animals in the wild or in a laboratory setting. This non-invasive nature also makes saliva samples particularly valuable for studying rare or endangered species, where minimizing stress and discomfort is a top priority. Furthermore, mammalian saliva samples can provide valuable insights into an organism's diet and feeding behaviors. For example, researchers can analyze the DNA and other molecules present in saliva to determine what a particular animal has been eating. This can be especially useful for studying the foraging habits of wild animals, as well as for understanding the dietary preferences of domesticated species. By understanding an animal's diet, researchers can gain a better understanding of its ecological role and the dynamics of its ecosystem. From a medical perspective, mammalian saliva samples can also offer important clues about an organism's health and well-being. For example, changes in the composition of saliva can beindicative of certain health conditions, such as periodontal disease or diabetes. By studying saliva samples from both healthy and diseased individuals, researchers can gain a better understanding of the biomarkers and other indicators of various health conditions, potentially leading to the development of new diagnostic tools and treatments. Another important aspect of studying mammalian saliva samples is their potential for understanding the evolution and diversity of mammalian species. By comparing the composition of saliva across different species, researchers can gain insights into the evolutionary relationships between different animals, as well as the adaptations that have allowed them to thrive in various environments.This can help us better understand the genetic and physiological factors that have shaped the diversity of mammalian life on Earth. In addition to their scientific and medical value, mammalian saliva samples also hold significant cultural and emotional significance for many people. In some cultures, saliva plays a symbolic and spiritual role, and studying saliva samples from certain animals can offer insights into traditional beliefs and practices. Furthermore, for many people, saliva is intimately associated with feelings of affection and bonding, such as when kissing a loved one or caring for a pet. Understanding the biological and chemical aspects of saliva can deepen our appreciation for these emotional and social connections. In conclusion, mammalian saliva samples are a valuable and versatile resource for researchers, offering insights into a wide range of biological, medical, and cultural phenomena. By studying the composition and properties of saliva, scientists can gain a better understanding of an organism's health, behavior, and evolutionary history, while also respecting the emotional and cultural significance of this bodily fluid. As technology and research methods continue to advance, the study of mammalian saliva samples is likely to yield even more valuable insights in the future.。

蚌埠“PEP”2024年小学4年级上册第六次英语第5单元寒假试卷[含答案]

蚌埠“PEP”2024年小学4年级上册英语第5单元寒假试卷[含答案]考试时间：80分钟（总分:100）B卷考试人：_________题号一二三四五总分得分一、综合题(共计100题)1、What is the name of the sweet dessert made from sugar and cream?A. MeringueB. PavlovaC. CheesecakeD. Tiramisu答案: C2、How many hearts does an octopus have?A. OneB. TwoC. ThreeD. Four答案:C3、填空题：The first female governor in the United States was ________ (娜奈·亨利).4、听力题：Astronomical observations have been made for thousands of ______.5、听力题：Black holes can be detected by observing their effects on nearby _______.6、填空题：The __________ (历史的传承价值) is vital for growth.7、What do we call the process by which organisms maintain a stable internal environment?A. HomeostasisB. MetabolismC. AdaptationD. Evolution8、填空题：The __________ (历史的启示) sparks creativity.9、听力题：The _____ (狗) is barking.10、听力题：My grandma loves to knit ____ (blankets).11、选择题：What is the capital of Armenia?A. YerevanB. GyumriC. VanadzorD. Vagharshapat12、填空题：The cat purrs when it is _________. (满足)13、听力题：The __________ is a body of water that is often calm.14、填空题：My dad is a skilled __________ (木匠) who builds furniture.15、听力题：The __________ is a region known for its fishing.16、听力题：The __________ is an important tool for environmental management.17、填空题：Mahatma Gandhi led India to independence through ________ (非暴力).18、听力题：I have an ___ (idea) for a project.19、选择题：What do we call the act of reading a story aloud?A. NarrationB. StorytellingC. ReadingD. Reciting20、填空题：A __________ (化学符号) represents an element in the periodic table.21、What do we call the act of designing buildings?A. ArchitectureB. EngineeringC. ConstructionD. Planning答案:A22、填空题：The bird chirps happily in the _______ (鸟儿在_______中快乐地鸣叫).23、听力题：The ______ is a powerful animal in the jungle.24、听力题：The Earth's crust is much ______ than the mantle.25、What is the primary color of a lemon?A. GreenB. YellowC. OrangeD. Purple答案:B26、听力题：The capital of Finland is ________.27、填空题：The _____ (木头玩具) is very colorful.28、What is the opposite of noisy?A. QuietB. LoudC. SoftD. Calm答案:A29、听力题：The school bell ________ at PM.30、Which season is coldest?A. SummerB. WinterD. Fall31、What do we call the process of combining two or more colors?A. BlendingB. MixingC. MergingD. Combining答案:B32、填空题：My dog likes to dig _______ (洞) in the garden.33、听力题：The __________ of a liquid is the temperature at which it boils.34、选择题：How many rings are on the Olympic flag?A. 3B. 4C. 5D. 635、填空题：My dad is a _____ (工程师) who works on projects.36、填空题：Kittens play with ______ (线球) all day.37、听力题：The _______ grows tall in the garden.38、What is the name of the famous rock formation in the Grand Canyon?A. El CapitanB. Half DomeC. Monument ValleyD. The Wave答案: D. The Wave39、填空题：Let’s _______ (一起) play a game.40、What is the capital of the Czech Republic?A. PragueB. BratislavaC. Budapest答案:A. Prague41、What is the largest planet in our solar system?A. EarthB. MarsC. JupiterD. Saturn答案:C42、听力题：Respiration is a chemical process that occurs in ________.43、听力题：The girl enjoys ________.44、Which of these is an insect?A. SpiderB. ButterflyC. WormD. Snail45、a Desert is located in ________ (撒哈拉沙漠位于________). 填空题：The Saha46、听力题：The chemical symbol for neon is ______.47、填空题：I can’t wait to show off my __________ (玩具名).48、What do you call a story that teaches a lesson?A. FableB. MythC. FairytaleD. Novel答案:A49、听力题：The ________ is a famous landmark in Paris.50、填空题：The owl is active at ________________ (夜晚).51、填空题：The _____ (竹子) grows very quickly.52、填空题：A wolverine is a strong ______ (动物).53、填空题：The ancient Egyptians utilized ________ (香料) in their rituals.54、What do we call the process of converting a gas to a liquid?A. MeltingB. FreezingC. CondensationD. Evaporation答案:C55、填空题：My friend is a _____ (记者) who covers important stories.56、填空题：My dad is a __________ (机械师).57、听力题：The park is ________ my house.58、填空题：My ________ (兄弟) plays football every weekend.59、填空题：Wildflowers grow without ______ (照顾).60、What is the capital city of England?A. ParisB. LondonC. MadridD. Berlin答案: B61、听力题：A vacuum is a space without ______ (matter).62、填空题：Turtles can live for a ______ (很长的时间).63、填空题：The _____ (草原) is home to many wildflowers.64、What is the main diet of pandas?A. MeatB. BambooC. FruitD. Fish65、填空题：My favorite toy is a ______ (火车).66、填空题：The _____ (熊猫) eats bamboo and is very adorable.67、填空题：The _______ (小狗) loves to play fetch with its owner.68、What do we call the practice of growing plants for food?a. Agricultureb. Horticulturec. Farmingd. Gardening答案:a69、填空题：The code of laws created by the ancient Greeks was called the ______ (德尔菲神谕).70、What is the opposite of hard?A. SoftB. ToughC. StrongD. Firm答案:A71、小刺猬) curls up when scared. 填空题：The ___72、What is the capital of the United States?A. New YorkB. Washington, D.C.C. ChicagoD. Los Angeles答案:B73、选择题：What is the opposite of “fast”?A. QuickB. SlowC. RapidD. Swift74、听力题：Gravity helps keep the planets in ______.75、填空题：I can ______ (保持) a balanced life.76、填空题：The sea turtle lays its eggs on the ________________ (沙滩).77、选择题：Which creature is known for spinning webs?A. AntB. SpiderC. BeeD. Fly78、听力题：The earth spins on its _______.79、听力题：She is wearing ________ shoes.80、填空题：A _____ (植物历史) can provide context for their importance.81、填空题：_____ (plantations) can impact local ecosystems.82、听力题：The chemical formula for iron(III) oxide is __________.83、听力题：The capital of Nauru is __________.84、填空题：Every morning, I eat ________ (早餐) before school.85、听力题：The ____ has a long beak and is often seen searching for food.86、填空题：I enjoy watching _____ fly in the sky.87、What do you call a young alligator?A. HatchlingB. PupC. CalfD. Kit88、填空题：There is a big _______ (树) in my backyard.89、听力题：The boy has a cool ________.90、听力题：I have a _____ (gift) for you.91、填空题：The ______ (老虎) is a strong and fast animal.92、听力题：Telescope lenses can magnify distant ______.93、What do we call the study of how living things interact with each other and their environment?A. EcologyB. BiologyC. ZoologyD. Botany答案: A. Ecology94、听力题：The boiling point of a substance is the temperature at which it ______.95、填空题：The __________ is so clear tonight; I can see many stars. (天空)96、听力题：The _____ (桌子) is made of wood.97、听力题：The ____ is a friendly animal that people keep at home.98、What is the name of the famous canyon in Arizona?A. Grand CanyonB. Antelope CanyonC. Bryce CanyonD. Zion Canyon答案: A. Grand Canyon99、听力题：The chemical formula for ferrous sulfate is ______.100、填空题：The ancient Egyptians had _______ to help them in the afterlife. (护身符)。

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a r X i v :a s t r o -p h /9807054v 2 10 J u l 1998A&A manuscript no.(will be inserted by hand later)1.IntroductionIn the last few years repeated observations of the galactic bulge region with coded mask hard X-ray telescopes have led to the discovery of many new sources.The larger number of X-ray sources in the Galactic Center direction,compared to other parts of the galactic plane,indi-cates the presence of an enhanced concentration of accreting binaries in a region where the overall mass density is higher than at larger galactocentric distances.Though most of these sources are basically of the same kind of the accreting low mass and high mass binaries found elsewhere in the Galaxy,a few of them turned out to be particularly interesting and peculiar objects ,like e.g.the “bursting pulsar”GRO J1744–28(Lewin et al.1996),the “microquasar”1E 1740.9–2942(Mirabel et al.1992),and the 2msec pulsar SAX J1808.4–3658(in’t Zand et al.1998a,Wijnands &van der Klis 1998).Here we report on the BeppoSAX MECS observation of a recently discovered bursting X-ray source located at an angular distance of 19ar-cmin from the Galactic Center direction.This source,named SAX J1747.0–2853,has been discovered with the Wide Field Camera instruments (WFC)on board BeppoSAX (in’t Zand etal.1998b)and has been later observed with both the Narrow Field Instruments (NFI)and the WFC instruments by Baz-zano and collaborators (Bazzano et al.1998).These authors also reported the presence of X–ray bursts from SAX J1747.0–2853.The data described here were obtained about 20days after the discovery of SAX J1747.0–2853,as part of our survey of the Galactic Center region with the BeppoSAX NFI (Sidoli et al.1998).2.Observations and Data AnalysisThe region of sky containing SAX J1747.0–2853was imaged with the MECS and LECS instruments during an observa-tion performed from April 13to April 15,1998.The MECS instrument (Boella et al.1997)is based on position-sensitive gas-scintillation proportional counters providing images in the 1.3-10keV energy range within a ﬁeld of view of 56arcmin diameter.After standard data selection and cleaning,the re-sulting net exposure time in the MECS instrument is 72ksec.As 1E 1743.1-2843was the main target of the observa-tion,the new source SAX J1747.0–2853was observed ∼13arcmin oﬀaxis,at coordinates R.A.=17h 47m 0.5s,Dec.=−28◦52′36′′,J2000(with an uncertainty of ∼1arcmin).This position is consistent with that obtained in the dis-covery observation with the WFC instrument (R.A.=17h 47m 02s,Dec.=−28◦52′.0,J2000,3′error radius,in’t Zand et al.1998)and subsequently reﬁned with the NFI ob-servations (R.A.=17h 47m 02s,Dec.=−28◦52′.5,J2000,1′error radius)by Bazzano et al.(1998).in’t Zand and cowork-ers noted that the source SAX J1747.0–2853is positionally co-incident,within errors,with the X–ray transient GX 0.2–0.2observed in outburst in 1976(Proctor et al.,1978).Some variability on a timescale of hours,as well as a strong burst,starting at 1:40:03UT of 1998April 15(see section 3),are clearly visible in the MECS background subtracted lightFig.1.SAX J1747.0–2853MECS light curve.The bin size is 200s.curves presented in ﬁgure 1.After converting the arrival times to the Solar System barycenter,we searched for coherent sig-nals in the X–ray ﬂux of the source.We ﬁrst removed the burst,then we accumulated a 0.3s binned light curve and calculated a single power spectrum over the whole observation following the method outlined by Israel &Stella (1996).No signiﬁcant pe-riodicity was found with a corresponding 99%conﬁdence level pulsed fraction upper limits between 25%–20%and 15%–17%for the 104s–100s and 100s–1s period intervals,respectively.We also performed a period search during the 25s long burst time interval even in presence of poorer statistics.In this case we accumulated a 0.5ms light curve and calculated the corresponding power spectrum.We found no signiﬁcant peak.The 99%conﬁdence level upper limits on the pulsed fraction are in the range 60%–40%and 35%–40%for the 1–500ms and 500ms–2s period intervals,respectively.To study the source spectrum we extracted the MECS counts within a radius of 2.5arcmin from the source posi-tion and rebinned them in order to have at least 20counts per bin.The time interval corresponding to the X-ray burst was excluded from the analysis.To properly ﬁt the count spec-trum,we derived the MECS response matrix appropriate to the source oﬀ-axis position and corrected for the adopted ex-traction radius.The latter was smaller than the usual 4arcmin in order to avoid regions of the detector aﬀected by the support strongback of the MECS window.The standard MECS background spectrum obtained from blank ﬁeld observations underestimates the actual backgroundpresent in regions of low galactic latitude.We therefore esti-mated the background spectrum from the region surrounding SAX J1747.0–2853observed in our data.The best ﬁt with an absorbed power law gives a photon index α∼2.4and an ab-sorbing column density of ∼1023cm −2.Though the formal uncertainties on these parameters are rather small,the results are somewhat dependent on the particular choice of the back-ground region.Therefore,the errors indicated in Table 1,where the results of the ﬁts are summarized,have been estimated taking the background uncertainty into account.The observed 2-10keV ﬂux is ∼2×10−11erg cm −2s −1.A slightly better ﬁt of the MECS spectrum can be obtained with a ∼6keV thermal bremsstrahlung.3.Analysis of the X-ray burstThe light curve of the X-ray burst is shown in ﬁgure 2;only the orbit containing the burst is displayed.At the burst peak the source reaches a count rate ∼500times stronger than the persistent emission.By ﬁtting the burst light curves in two en-ergy bands,we derived exponential decay constants of ∼15s and ∼10s at energies respectively below and above 4.5keV.The average spectrum of the burst is harder than that of the persistent emission (power law photon index ∼1.7).In ﬁgure 3we show the results obtained by ﬁtting the burst emission in diﬀerent time intervals with a blackbody spectrum.The contri-bution from the persistent emission has been subtracted.The spectral softening seen in the light curves is conﬁrmed by the spectral analysis that shows a temperature variation from ∼2Table 1.Persistent emission spectral analysis (errors are 90%c.l.).Model Column density parameterRed.χ2Unabsorbed Flux (2–10keV)(1022cm −2)(138d.o.f.)(10−11ergs cm −2s −1)Power law 9.9+0.8−0.8αph =2.4+0.1−0.1 1.094.8+0.2−0.3Bremsstrahlung8.3+0.6−0.3T =6.1+0.9−0.7keV1.014.0+0.2−0.3to ∼0.5keV.Assuming an Eddington luminosity at the burstpeak,we obtain a distance of ∼10kpc.Besides,assuming a spherical emitter at a distance of ∼10kpc,we determine a blackbody radius consistent with the canonical radius for a neutron star.Moreover,this value remains constant during the burst.1SAX J1747-28530.010.101.0010.00100.00C t s /s(a) total band 0.1-10 keV0.010.101.0010.00100.00C t s /s(b) band 0.1-4.5 keV01:420.010.101.0010.00100.00C t s /s01:3801:4001:4401:4601:4801:5001:52UT hrs of day 1998-Apr-15(c) band 4.5-10 keVFig.2.Light curve of the burst in the total,soft and hard bands (panels a,b,c respectively).The minimum bin size is 1.5s,but data have been rebinned for clarity in such a way that each bin has at least a statistics of 5sigma during the burst decay (all bands),and a statistics of 2σ(panels a,b)or 1.5σ(panel c)during the burst onset.The dotted and dashed lines indicate the level of the persistent emis-sion in the contiguous interval (uninterrupted by Earth occultation or SAGA passage)respectively before and after the burst.4.DiscussionThe properties of the burst observed from SAX J1747.0–2853are typical of type I X-ray bursts and allow to clearly classify this source as a neutron star in a Low Mass X-ray Binary.It is in fact widely believed that the type I X-ray bursts result from thermonuclear ﬂashes on the surface of accreting neutron stars (see,e.g.,Maraschi &Cavaliere 1977,Lewin et al.1992).1SAX J1747-28530.00.51.01.52.02.53.0k T (k e V )(a) Temperature051015r (k m )(b) Radius (@ 10 kpc)01:3801:4001:4201:4401:4601:4801:5001:52UT hrs of day 1998-Apr-150.010.101.00L (1038 e r g /s )(c) Luminosity (@ 10 kpc)Fig.3.Evolution of temperature,luminosity and blackbody radius during the SAX J1747.0–2853burst.For luminosity and radius a distance of 10kpc was assumed.Considering its galactic coordinates,the high absorption,and the properties of the burst,it is likely that SAX J1747.0–2853be at a distance comparable to that of the galactic cen-ter.For a distance of ∼10kpc,also the ﬂux of ∼5×10−10erg cm −2s −1observed during the previous BeppoSAX obser-vations (Bazzano et al.1998)is consistent with the typical luminosity of X-ray bursters (1036–1037erg s −1).At the time of the observation we present here,the ﬂux had decreased by about a factor ten with respect to the ﬁrst NFI observation by Bazzano et al.(1998),consistent with an exponential decay with e-folding time of ∼8days (Fig.4).Unfortunately,the poor coverage of the light curve does not allow to determine the shape of the outburst.No other X-ray sources at this position have been reported previously,with the exception of the transient GX 0.2–0.2,that was active for a few months in 1976(Proctor,Skinner &Willmore 1978,Cruddace et al.1978).GX 0.2–0.2was ob-served with rocket-borne instruments with limited angular res-olution and more precisely located with the RMC instrumenton the Ariel V satellite.The Ariel V position of GX0.2–0.2 (90%conﬁdence radius∼1.5arcmin)is consistent with that of SAX J1747.0–2853.Although it cannot be excluded that diﬀer-ent sources were observed,it is very likely that SAX J1747.0–2853and GX0.2–0.2are the same object,as already pointedout by in’t Zand et al.(1998b).No bursts were observed from GX0.2–0.2in1976,but the peak luminosity,the duration of the ouburst and the relatively soft spectral shape(Proctor, Skinner&Willmore1978)were similar to those observed in SAXJ1747.0–2853.Fig.4.SAX J1747.0–2853recent BeppoSAX detections.Theﬁrst threeﬂuxes are taken from in’t Zand(1998b,ref.1)and Bazzano et al.(1998,ref2.).In ref.1and ref.2ﬂux uncertainties are not reported;our errors are smaller than the symbol used.Inﬁgure5theﬂuxes observed in1976and1998are com-pared with several upper limits that we have derived from published observations of the Galactic Center region.All the ﬂuxes have been converted to the2-10keV band assuming the spectral parameters of our bestﬁt.The SIGMA observations (Goldwurm et al.1994)obtained at E>40keV have not been reported since the corresponding upper limits(∼0.6−3×10−9 erg cm−2s−1)are not very constraining when extrapolated to lower energies with such a soft spectrum.For a diﬀerent reason, i.e.the strong interstellar absorption,also the ROSAT data are not very useful to constrain the luminosity of SAX J1747.0–2853.5.ConclusionsUsing the MECS on–board BeppoSAX we detected a type I X–ray burst from the recently discovered source SAX J1747.0–2853.The estimated position supports the identiﬁcation with the transient GX0.2-0.2observed in1976.The X–ray burst is clearly indicative of the presence of a neutron star accreting matter from a low mass companion.The analysis of the burst properties allow to estimate a distance to the source of∼10 kpc,that place SAX J1747.0–2853close to the Galactic Cen-ter.The severe interstellar absorption in this region hampers the search for the optical counterpart.Applying the relation N(HI+H2)/A V=1.9×1021cm−2mag−1(Bohlin,Savage and Drake1978),we estimate an extinction of∼50mag,which Fig.5.SAX J1747.0–2853detections and upper limits from1975 to1998.References are:(1)Proctor et al.78;(2)Watson et al.81;(3)Skinner et al.87;(4)Pavlinsky et al.94;(5)in’t Zand et al.98b;(6)Bazzano et al.98.means an apparent J magnitude>30for the low mass compan-ion.ra Sidoli thanks Annamaria Borriello for help and useful discussions.ReferencesBazzano A.et al.1998,IAU Circ.n.6873Boella G.,Butler 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