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
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
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
Tsys = TN + Tbg + Tsky + Tspill + Tloss
Radiometer Equation
S/N = Tsource / Trms
Observing Mode
•Position Switch
Trms = 2 Tsys / sqrt (t * Δν)
!
•Frequency Switch
!
❖ How good is our data?
射电观测波段
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
!
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
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
(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
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?
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)
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
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?
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
ηA = Aeff/Ag
!
P = ½ Aeff Δν Sν
!
a
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
!
!
•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