射电天文学

Bell Discovered Pulsars
(b)
脉冲星
Bell @ IAU and NAOC
M. Ryle
综合孔径
Molecular Universe (c)
OH
Weinreb et al. 1963 Nature
CO
Penzias, Jefferts, Wilson 1970, ApJL
中性氢探测宇宙大尺度结构
Chang et al. 2010, Nature, 466, 463
Pritchard & Loeb 2010, Nature, 468, 772
中性氢探测宇宙频谱
Bowman & Rogers 2010, Nature, 468, 796
发现
(a)
Cosmic Microwave Background (CMB)
!
!
•OTF
Trms = sqrt(2) Tsys / sqrt (t * Δν) Trms = sqrt(2) Tsys / sqrt (t * Δν)
主要的单天线射电望远镜
Parkes 64m
GBT 100m
Effelsberg 100m
Lovell 76m
IRAM 30m
Arecibo 300m
ηA = Aeff/Ag
!
P = ½ Aeff Δν Sν
!
P = k TA Δν
!
天线精度
Ruze Formula
Rule of Thumb: The RMS surface error should be < ~ 1/12
of the wavelength
Antennas
天线温度和系统噪声温度
天线温度仅仅是天线输出功率的另一一种表示示
PA = kTAΔν
天线温度TA = 1K, PA = 1.38 10-23 WHz-1 典型射电源辐射天线输出功率
天线指向天空背景时，有功率输出 包括：天空背景 Tbg; 大大气气辐射 Tsky; 地面面辐射 Tspill
馈源和波导损失 Tloss; 接收机噪声 TN
!
❖ How good is our data?
射电观测波段
Baidu Nhomakorabea
10 - 300 MHz 1. - 110 GHz
100 - 300 GHz 300 - 1000 GHz 1 - 6 THz
low freuency
0.30-0.34
P
1.24-1.70 L
2.65-3.35 S 4.0-8.0 C 8.1-8.8 X 12.4-15.3 Ku 15.0-26.5 K
瑞利判据：
射电天线对一一颗射电源响应的主瓣极 大大值处刚好与另一一颗射电源紧邻主瓣 的第一一极小小值重合，即角角分辩率值为 主瓣宽度（BWFN）的一一半
抛物面面：
1 WBFN 2
= 1.219
λ D
HPBW = 1.02 λ D
流量密度
流量密度 w m-2 Hz-1 1 Jy ＝ 10-26 w m-2 Hz-1
(a)
Harold Irwin Ewen and Edward Mills Purcell
1951
Transit telescope designed to have the Galactic Center pass through its beam
!
开创了星际介质、银 河系动力学结构、恒 星形成及星际化学等 许多天文领域
2015
the Paths
! !
How do we know we know?
Epistemology
⃷䠭㤐㧪岥㉬䥥ּ 岥㉬㤐⛐庅座䥥ּ 岥㉬䥥庅座㤐⛐⇆拻抨䫵䵗㩆抟㓱䥥
–李菂之“研究生生”三公理
&QGU5VCT(QTOCVKQP/CVVGT!
The “Visible” Universe
Weinreb @ NAOC
射电天体物理
(a) 中性氢星系、
宇宙学
(b) 脉冲星
(c) 星际介质演化
及恒星形成
A, B, and C
❖ What are we looking at?
!
❖ Where are we looking at?
!
❖ How strong is the source?
A, B, and C
•What are we looking at?
A Fourier transform of time series
!
•Where are we looking at?
!
Beam map and uncertainty principle
!
•How strong is the source?
!
Antenna temperature
!
•How good is our data?
Radiometer Equation + observing modes
辐射转移和激发
✦辐射转移
✦发射系数，吸收系数，背景
! !
✦激发
✦ 碰撞，辐射
HI vs Dense Clouds
Lilley 1955
Anderson et al. 1991
Tsys = TN + Tbg + Tsky + Tspill + Tloss
Radiometer Equation
S/N = Tsource / Trms
Observing Mode
•Position Switch
Trms = 2 Tsys / sqrt (t * Δν)
!
•Frequency Switch
Credit: M. Blanton and the Sloan Digital Sky Survey.
9JCVCTGVJGUGŅJQNGUņKPJGCXGP!
Speculation of Gaseous ISM
Van der Hulst (1945)
Shklovski (1948)
发现 Atomic Hydrogen (HI) in Space
1954: Self Absorption
Discovery of Massive Cold HI Clouds
26.5-40 Ka
30-50
Q
50-75
V
75-110
W
mm
sub-mm
THz
射电信号的流程
射电信号 地球大大气气
天线 接收机 采集系统
计算机 天体物理信息
Fourier Transform
Delta Gaussian
Square Wave
抛物面天线功率方方向图
射电望远镜空间分辩率
射电望远镜能区分两个射电点源所对 应天空最小小的张角角称为角角分辨率