小知识备忘（不知道什么时候会整理）

Danger: Work that is not published is lost in most cases.

Publish or perish?!

标长(scale length): $n(R) \sim exp(-R/h_{\rm R})$, $h_{\rm R}$为标长，即沿银盘方向向外移动$h_{\rm R}$，恒星密度下降e倍。
标高(scale height): 类似于标长，垂直于银盘方向，当恒星密度下降e倍时候的高度。薄盘指的是所有年轻大质量恒星所定义，而厚盘指的是其余恒星的定义。
银河系黑洞质量约为$4\times 10^{6}$M$_{\odot}$. Galactic year (cosmic year): 太阳绕银心一周所需要的时间，$\frac{2\pi \times 8.4\;kpc}{240\;\rm km/s} \sim 200 Myr$。
Sonic scale taking B into account: $\lambda_{\rm sonic} = L[\frac{c_{\rm s}}{\sigma_{\rm v,3D}}(1+\beta^{-1})]^{2} $ (Federrath2016)
主序恒星质量半径关系：$R \sim R_{\odot}(\frac{M}{M_{\odot}})^{0.7}$, 主序恒星半径约为0.1--25R$_{\odot}$
主序恒星质量光度关系：$L \sim L_{\odot}(\frac{M}{M_{\odot}})^{\alpha}$, 当$M\le M_{\odot}$时$\alpha \sim 5$, 当$M_{\odot}\le M\le 10M_{\odot}$时$\alpha \sim 3.9$, 当$M\gt 10M_{\odot}$时$\alpha \sim 2.2$.
黑体谱峰值位置： $\lambda_{\rm max}=[2.9/T(K)]$mm, 太阳6000K对应的是5000埃.
相对太阳的丰度： [A/B] = log$_{10}${$\frac{(N_{\rm A}/N_{\rm B})_{*}}{(N_{\rm A}/N_{\rm B})_{\odot}}$}, Z$_{\odot} \sim$0.02.
三角视差距离：以周年视差测距定义秒差距，即: 1"=$\frac{1AU}{1pc}$, 则在1kpc处1个角分的距离为60000AU或者是0.3 pc (1pc=206265AU).
Luminosity: $L = 4 \pi D^{2} S$
22 GHz water maser luminosity: $L_{\rm H2O}/L_{\odot} = 2.3\times 10^{-8} [\frac{\int S_{\nu}dv}{\rm Jy\;km s^{-1}}][\frac{D}{\rm kpc}]^{2}$
磁场：尘埃消光：偏振平行磁场；尘埃热辐射：偏振垂直于磁场。
啥是星际介质? 在太阳附近， 10 pc³内只有一颗恒星，而太阳直径仅仅10^-7pc,所以大部分星际空间内是没有恒星的，但是它们充满了气体和尘埃，这就是我们所要研究的星际介质。
等强度线R₂₅, B band, 25 mag,测量大小。
哈勃时间Hubble time, $t = 1/H_{0}$,约137亿年。
暗物质的可能来源是WIMP, 弱相互作用有质量的粒子，如，中微子等。
为什么早期宇宙中质子比反质子多一点？？？
宇宙微波背景辐射来着与正反质子湮灭产生的光子。
接收机系统
模数转换器即A/D转换器，或简称ADC，通常是指一个将模拟信号转变为数字信号的电子元件。模拟信号是一串连续分布的振幅，而数字信号是离散取值的分布，因而转换的时候是有压缩的。
NOEMA，4730欧元一小时。30米是1/3。From J.Z.Wang.
HEMT v.s. SiS接收机: HEMT就是低温低噪声放大器，直接把观测信号放大，然后再用低温或者常温的混频器，将观测信号下变频然后处理。HEMT因为自身有30dB的增益，所以链路后边噪声贡献很小，可以用常温混频器。优势是低温集成不需要有超导混频器，不需要有本振功分器等，系统简单了很多。现在sis的噪声大概是HEMT的一半，这是唯一的优势。将来估计200GHz以内，HEMT都会主导。From Yuan Ren。
样条插值是使用一种名为样条的特殊分段多项式进行插值的形式。From Guangxing
CRRL and [CII] fine structure lines basically trace the same gas. The difference is mainly from the observed intensity. [CII] is much stronger. From K. M. Menten
For a new Macbook, in case of issues with gfortran ("ld: library not found for -lSystem"). Mac Xcode install and command line tools needed to be installed respectively.
What is the CO-dark gas?
Answer:: The mass of molecular gas in an interstellar cloud is often measured using line emission from low rotational levels of CO, which are sensitive to the CO mass, and then scaling to the assumed molecular hydrogen H₂ mass. However, a significant H₂ mass may lie outside the CO region, in the outer regions of the molecular cloud where the gas-phase carbon resides in C or C+. Here, H₂ self-shields or is shielded by dust from UV photodissociation, whereas CO is photodissociated. This H₂ gas is “dark” in molecular transitions because of the absence of CO and other trace molecules, and because H₂ emits so weakly at temperatures 10 K < T < 100 K typical of this molecular component. This component has been indirectly observed through other tracers of mass such as gamma rays produced in cosmic-ray collisions with the gas and far-infrared/submillimeter wavelength dust continuum radiation.
Under the optical thin approximation (Goldsmith+2012), the C+ column density can be estimated from [CII] with N_C+ =1.1e16I, where I is the integrated intensity in units of K.km/s, the kinetic temperature is assumed to be 100 K, and the density is assumed to be 5e3 cm^-3.
巨星支在HR图中是垂直的，所以通过分光时差来测量距离的误差较大，最佳的情况下，绝对星等有0.5 m的误差，所以距离精度会达到25%。
RATRAN can be installed with CRETE github
radio recombination lines
The H109$\alpha$ line was first detected by P. Mezger in 1965, despite (incorrect) theoretical predictions that pressure broadening would smear out the lines in frequency and make them undetectable. It is true that atomic collisions in the interstellar medium significantly disturb the energy levels of large atoms, but this disturbance is about the same for adjacent energy levels, so the differential disturbance that alters the line frequency is actually much smaller. His advice: “Don’t abandon an observation just because you have been told that it will fail.”
The RRL has a Voigt profile with line width (Gordon & Sorochenko 2002):
$\Delta v_{\rm rrl} = 0.534\Delta v_{\rm pre} + (\Delta v_{\rm tur}^{2}+\Delta v_{\rm the}^{2}+0.217\Delta v_{\rm pre}^{2})^{1/2}$
where, "rrl", "pre", "tur", "the" represent the line width of radio recombination lines, pressure broadening, turbulence broadening, thermal broadening.
And the pressure broadening can be assessed with the formula of Brocklehurst & Seaton (1972):
$\Delta v_{\rm pre} = 4.287 (\frac{n}{100})^{7.4}(\frac{10^{4}}{T_{\rm e}})^{0.1}(\frac{n_{\rm e}}{10^{4}}) (km/s)$, where n is the principle quantum number, Te is the electron temperature, and ne is the electron density.
Doppler tracking: velocity reference frames and the definition of different velocities used in radio astronomy.
天马65m
2012年10月26日 first light
接收机： 1-50 GHz， 8个波段
主动面板系统
虽然在L波段有RFI，但是OH可做，C波段完全没有问题。Chat with Yan Sun, 6 GHz 以下RFI非常严重，高频所受影响较小。
HI 第一次发现是通过frequency switch得到的，因为银道面附近有大量的HI发射，难以得到干净的off点，之前的position switch尝试并不好。
Cosmic dust
Fluffy aspect or more spherical shpae for pure grains. Grain size ranges from a few A to a few micros.
Silicate (硅化物): Amorphous Fe/Mg-Silicates Forsterite (Olivine - Mg₂SiO₄) Enstatite (Pyroxene - MgSiO₃) Oxides: Alumina (Al2O3) Spinel (MgAl2O4) Wuestite (FeO) Hibonite (CaAl12O19) Rutile (TiO2) Carbides: Silicon Carbide (SiC) Titanium Carbide (TiC)
Bayes analysis: P(Girl|pants) = P(Girl)*P(pants|Girl)/(P(Boy)*P(Pants|Boy) + P(Girl)*P(pants|Girl))
南极天文台
median PWV = 0.14 mm 南极， 1 mm Mauna Kea, 0.5 mm ALMA
For frequnecy switching of IRAM30m, the offsets of 7.14 MHz, 11.7 MHz, 14.28 MHz are the best values for E090, E150, and E230. from Pepe Cernicharo?
甘氨酸是最简单的氨基酸，所以是目前天体化学的圣杯，Glycine, NH3CH2COOH.
The system temperature of a telescope can be estimated with the equation,
$T_{\rm sys} = (T_{\rm r} + T_{\rm sky})/(exp(-\tau))$,
where $T_{\rm r}$ is the receiver temperature, $T_{\rm sky}$ is the sky temperature inside the atmosphere ($2.73*exp(-\tau)+T_{\rm a}*(1-exp(-\tau))$), $\tau$ is the opacity, and $T_{\rm a}$ is the atmosphere effective temperature.
SKYDIP (Tipping): measure the optical depth of atmosphere at zenith (Wilson, T. L., Tools of Radio Astronomy).
$T_{\rm abs}(z) = T_{\rm rx}+\eta T_{\rm atm}(1-e^{-\tau_{0} sec(z)})+T_{\rm amb}(1-\eta)$.
This can be converted to $V_{\rm abs}(z) = -V_{\rm atm} e^{-\tau_{0} sec(z)}+ (V_{\rm rx}+V_{\rm atm})$. With this equation and measurements of $V_{\rm abs}(z)$ and z at different zenith angles, we can fit $\tau_{0}$ and other constants.
A source can reach the highest EL: $EL=90-|\phi - \delta|$, where $\phi$ is the latitude and $\delta$ is the declination.
Calculating the size of fits files and data rates:
NXPIXEL x NYPIXEL x Channels x 4 bytes (data size)
Σ(Npol x basebands x Channels x 4 bytes)/tdump (data rate)
wiggle baselines: the distance between the primary and secondary focus is about 50m, leading to a standing wave with a period of 3e8/50/1e6 MHz in Effelsberg spectra.
The N2H+ ion is mainly formed through reactions between H3+ and N2. It is mainly destroyed by N2H+ + CO ---> HCO+ + N2.
The solid angle is 1.133$\theta^{2}$.
To upgrade packages of pip, pip install aplpy --upgrade.
To upgrade pip itself, pip install --upgrade pip.
In case that MAC OS lack python-dev, try "xcode-select --install".
down the whole directory, wget -c -r -np -k -L -p /the/directory/url/
for Synchrotron Emission which is highly linearly polarised, this emission is parallel to E, and thus perpendicular to B.
13C fractionation into CO at low temperatures due to the reaction:
13C+ + 12CO ---> 13CO + 12C+ erengy (35 K)
Notes on Imagemagick: create a gif movie
/usr/local/bin/convert -resize 50% -delay 5 -loop 0 *png try.gif
Main beam efficiencies change from compact sources to extended sources (increasing). Greve+1998
Notes on Linus command lines
replace a string in multiple files in Linux:
sed -i 's/foo/bar/g' *.txt
replace all "foo" in *.txt with "bar".
Merge pdf files
gs -q -dNOPAUSE -dBATCH -sDEVICE=pdfwrite -sOutputFile=merged.pdf *pdf
gs -sDEVICE=pdfwrite -sOutputFile="output.pdf" -dNOPAUSE -dEPSCrop -c "<> setpagedevice" -f *.eps -c quit
Using VNC:
vnc
vncserver -geometry 1360x850 -depth 16 :1
..password..
ssh -g -L 5902:ip1.ip2.ip3.ip4:5901 portal.mpifr-bonn.mpg.de -l ygong
..password..
command+K
vnc://localhost:5902
copy files from remote ip with different ports:
rsync -rvz -e 'ssh -p xxxx' --progress * xxx@ip1.ip2.ip3.ip4:~/
Tunneling scp: In terminal 1, > ssh -A ygong@portal.mpifr-bonn.mpg.de # enabling the forwarding
In terminal 2, > scp -o ProxyJump=ygong@portal.mpifr-bonn.mpg.de myfile ygong@mcn15:/diskb/ygong/ # directly toward mcn15
Planck data

Ionization potential and dissociation energy

H₂CO -- 4.2e4 K (3.6eV).
ibus installation in Ubuntu
sudo apt-get install ibus-pinyin
ibus restart
ibus-setup (add shortcut)
system Setting --> Languague support --> Chinese (Pinyin)
Check Keyboard input method (add Pinyin)
Notes on Class projection none
If the projection is not defined, we can use the commands below
set variable position wirte
let R%HEAD%POS%PROJ 7
modify position 80.40 0.50
Notes on How to install RATRAN
1. download related files and tar the file
2. cd to the directory and ./configure
3. change "sky.make.lnx" with "MIRLISB = 'mirlibs' "
4. Install Miriad and configure Miriad
5. try with amc and sky.
Why can low-mass YSOs be used to derive parallax with VLBA?
Answer:: Low-mass young stars often generate non-thermal continuum emission produced by the interaction of free electrons with the intense magnetic fields that tend to exist near their surfaces (see the review, Feigelson & Montmerle 1999). This can make them very bright so that they can be detected by VLBI measurements.
Mass-loss rate of AGB stars
The formula to estimate the mass-loss rates using CO lines can be found in Ramstedt+2008, De Beck+2010, and the references therein.
Detection of CO in LMC AGB stars (Groenewegen+2016).
Ammonia
The formula to estimate the ammonia column density can be found in Harju+1993 and Mangum+1992
hot corinos: inside Class 0 low-mass stars, densities > 1e7 cm-3, temperature >100 K, and typical size of <150 AU (Ceccarelli, C.+2004).
spatial power spectra: L~1/lambda, the pixel resolution in the fft domain is determined by the maximum angular scale.
RFI: airborne radar from planes (4.1--4.3 GHz)
In case that the html created by the CASA pipeline does not work
1. firefox/chrome open the html file.
2. python3 -m http.server 3. localhost:8000 in the browser
uGMRT: 250-500 MHz
molecules: 3N-6 vibrational modes for a polyatomic molecule, and 3N-5 vibrational modes for a linear molecule
unsaturated and saturated masers (Colom+2018)
For single lines associated with an unsaturated maser, an increase in the flux density F is accompanied by narrowing of the line : $\Delta V \propto (ln F_{0})^{-1/2} $
In the case of a saturated maser, $\Delta V \propto F_{0}^{-1/2} $
Here, F0 is the flux at the line center.
Firefox issues that I met a few times: "Firefox is already runnning but not responding. To open a new..."
delete the two lock files in the profile folder:
>cd ~/.mozilla/firefox/xxxxxx/
>rm lock .parentlock
Transparent orange stuff occupying half of my screen in Ubuntu 24.04
Disable Enhanced Tiling in the settings, Ubuntu Desk top, or use "gnome-extensions disable tiling-assistant@ubuntu.com"
Four golden lessons by Steven Weinberg
1. No one knows everything, and you don't have to.
2. go for the messes.
3. forgive yourself for wasting time.
4. learn something about the history of science, or at a minimum the history of your own branch of science.
Tell students before they write paper
1. Do not copy, or it will affect your career.
2. Read your draft first, and then send it to your collaborators.
3. the minus line should be longer. e.g. -45 --> $-$45.
4. Only variables should be given in italic. Subscripts, superscripts, units, and constants should be given in Roman. e.g., $T_{ex}$ --> $T_{\rm ex}$.
Questions to be answered (collected from different talks and websites):
1. Formation of molecular clouds
2. Origin and statistical characteristics of ISM turbulence.
3. Star (cluster) formation in molecular clouds and at different scales.
4. Origin of stellar initial mass function.
a. where, when, and how do molecular clouds form?
b. what are molecular cloud properties?
c. how do stars form in their interior?
d. what determine the Kennicutt-Schmit (Gao-Solomon) relation?
e. What are the structure, dynamics, energy balance, and chemistry of the clouds?
f. What are the characterized scales of turbulence in the ISM？
g. Are there differences between low and high-mass star-forming clouds?
h. A census of star-forming cores.
i. the energy balance of gas heating and cooling.
j. the impact of sub-solar mentalities.
k. different phases of the ISM.
l. isotopic ratios (e.g., C/N/O/Si/S) to trace the chemical evolution of the Galaxy.
Observational notes for well-known sources
Orion KL, "hot core": J2000 RA=05:35:14.5, DEC=-05:22:30 (off: 900",0)
TMC-1 (CP): J2000 RA=04:41:42.5 , DEC = 25:41:2 (off: 720", 720")
IRC +10216: J2000 RA=09:47:57.4 , DEC= 13:16:43.8 (off: 600", 0)
SgrB2: J2000 RA=17:47:19.8 DEC=-28:22:17 (off: -3600", 0) only 60' East Azimuth Hollis+2006
In case of Anaconda-gfortran crashed with gfortran-7, reconfigure Anaconda manually, put Anaconda--PATH in the last line
Zeeman effect
I should create an ADS library including published Zeeman measurements. Here are some to be added, Schwarz+1990, Killeen+1992, Plante+1995, Bourke+2001, Crutcher+1996, Crutcher+1996, Crutcher+1999, Crutcher+2012, Crutcher+2010, Crutcher+2000
6.7 GHz maser flare sources
M2O papers
G358.931-0.030
PAPERS
Monitoring
G24.33+0.14
PAPERS
info