19
votes
Accepted
What is sin i in this graph and why is it there?
If you discover an exoplanet via the Doppler (radial velocity) method, then the amplitude of the radial velocity variations depends on the inclination, $i,$ of the exoplanet's orbital axis with ...
- 118k
12
votes
Accepted
How do you propagate asymmetric errors? (on the practical way to...)
I'm not sure this question really belongs here, but you mention the word "astronomy", and I'm an astronomer and I have an opinion on how to add numbers with asymmetric uncertainties:
...
- 33.8k
11
votes
Accepted
Locate stars in sky from list of (x, y) co-ordinates
Upload your photo to nova.astrometry.net and in a few minutes you will get a result page that tells you the plate scale in arcseconds/pixel, the celestial coordinates of the center of the frame, the ...
- 1,450
8
votes
Accepted
What is z in this program?
Welcome to the world of software developed by scientists for their own use.
There are not many clues.
The top-level README cites Nemravová et al. 2016.
That paper mentions PYTERPOL briefly in section ...
- 16.6k
5
votes
How to interpret this spectrum of the "new DESI Quasar at z = 6.53"; what causes the big edge at about 9150 Angstroms?
Thomas' answer is completely correct, I'd just like to elaborate a little on the reason for such a spectrum.
Quasar spectra generally have broad emission lines, in particular Lyman $\alpha$ at a rest ...
- 33.8k
5
votes
How to interpret this spectrum of the "new DESI Quasar at z = 6.53"; what causes the big edge at about 9150 Angstroms?
The jump occurs at the redshifted wavelength of the Lyman-$\alpha$ line, so this is the Gunn-Peterson trough, which is caused by neutral hydrogen in the intergalactic medium suppressing any radiation ...
- 2,318
5
votes
Examples of the oldest "precoveries"; objects that were first discovered in recent data but then looking back are confirmed in much older data
If handwritten notes of visual observation are valid, a good candidate is the observation of Neptune by Galileo in 1612, 234 years before the actual discovery.
Also available without paywall here
- 151
5
votes
Accepted
Procedures to test an hypothesis
A solution would be attempts at measuring those parameters directly for a large number of disks (not possible at the moment, except for a few cases and few variables) or use population synthesis ...
- 9,088
5
votes
Is there a centralized database of all stars?
The SIMBAD database hosted by the Centre de Donnees Astronomique de Strasbourg is the closest you are likely to find to a centralised database.
http://simbad.u-strasbg.fr/simbad/sim-basicIdent=m33&...
- 118k
4
votes
Accepted
Extracting specific star data from Gaia DR2?
You can do this via VizieR (main site at CDS, Strasbourg, France linked; worldwide mirrors are available). You can search by catalog name from that form or enter ...
- 7,250
4
votes
Accepted
How did astronomers "measure a large (>40 degrees) misalignment between the black hole spin and the orbital spin" of MAXI J1820+70?
See Figure 3 from https://arxiv.org/pdf/2109.07511.pdf:
In this picture, the North and East directions are in the plane of the sky, and the $\hat{o}$ direction is in the direction of the observer. In ...
- 316
4
votes
Accepted
How do you tell if a variable star is periodic or not by its light curve?
There are some nice and well-tested routines to create periodograms and test the periodicities for significance in the astropy.timeseries package, containing the LombScargle class.
This class includes ...
- 118k
4
votes
Accepted
How to get phase-folded data (-0.5,0.5)?
Take your final result for the phase and then subtract 1 if it is $>0.5$.
- 118k
4
votes
How to get phase-folded data (-0.5,0.5)?
Let's see if this is what you need:
Starting with
phi = ((HJD-T0)/P)%1
rewriting in MathJax:
$$\phi = \mod((H_{JD} - T_0) \ / P, \ 1)$$
We just need to push it ...
- 31.8k
3
votes
Accepted
How to convert spectra to log-wavelength and interpolate them into linear spacing in log-wavelength
If your limits in wavelength are $\lambda_1$ and $\lambda_2$, then take the log of these and then divide your x-axis into $n$ bins with equal steps in log wavelength.
If you already have your spectra ...
- 118k
3
votes
Accepted
How do I phase fold the light curve for a variable star?
"Phase folding" is just a procedure whereby you replace the time-axis values by t % P, where P is the period and % is the modulo operator that returns the remainder of t/P.
There are are a ...
- 118k
3
votes
How and where can I get the continuum and/or FITS data for Jupiter and Saturn from ALMA, GMRT and VLA Telescopes?
Most observatories have their own separate data archives, so you’ll likely have to do three separate searches. Here’s a query for Jupiter in the ALMA archive: https://almascience.nrao.edu/aq/?...
- 4,744
3
votes
How to fit LOSVD of a galaxy with gauss hermite parametrization
If you read the documentation for the curve_fit function, you’ll see that it has an optional parameter (p0) for the initial ...
- 14.9k
3
votes
Are chirped gravitational wave events generally first identified by searching through libraries of chirps?
LIGO/Virgo has multiple detection pipelines. Several of them (GstLAL, MBTA, PyCBC Live and SPIIR) are "modelled" searches which use large grids of pre-computed models to compare the signal ...
- 1,281
3
votes
Accepted
What does "RV model including a GP with a quasi-periodic covariance structure" mean?
What does "RV model including a GP with a quasi-periodic covariance structure" mean?
RV stands for radial velocity, which is an often used quantity in exoplanet science - it is a usual ...
- 3,989
3
votes
Accepted
How to plot 68% contours?
From your comment I would take that you already know how to plot contours in python, but are not sure, at what level/height to plot them to get a 1-sigma/68% contour.
The answer you can find, e.g., in ...
- 2,548
3
votes
Accepted
Downloadable GCNS (Gaia Catalog of Nearby Stars)
Perhaps I am late, but the GCNS is available via VizieR. The data can be both queried there and downloaded via FTP: https://cdsarc.cds.unistra.fr/viz-bin/cat/J/A+A/649/A6#/browse, theoretically it is ...
- 146
3
votes
Why Nyquist Sampling Rate depends on Bandwidth and not max frequency?
This is a great question and sampling is always a little tricky.
side note: It's important to make sure that no down-conversion has been done, that the " 1000-1400 MHz band" has not already ...
- 31.8k
3
votes
How does the Hubble Space Telescope measure the speed of the wind inside Jupiter's Great Red Spot?
There's nothing special happening to determine the velocity: Several pictures are taken, e.g. each Jovian day and the distance some features in the clouds have moved is calculated. For that, image ...
- 382
2
votes
Accepted
How to calculate an infrared SED from the specific intensities?
Say that you have an image with $N \times N$ pixels that covers a region of sky of $\theta \times \theta$ steradians. For each pixel $i$ you have a value of flux density $J_i$, expressed in Jy/sr. The ...
- 3,840
2
votes
Accepted
Why histogram does not look like the Gaussian curve?
I hope that someone more knowledgeable than me will answer this question, but this is what I understand it is happening.
The bootstrap method gives an estimate of the probability distribution of the ...
- 3,840
2
votes
Are chirped gravitational wave events generally first identified by searching through libraries of chirps?
If I’m understanding everything about what you’re asking and how it relates to this other thing, I believe a kind of library you’re thinking of refers to a surrogate model.
The idea behind a surrogate ...
- 2,647
2
votes
What are the applications of cross matching astronomical catalogues?
I did work in the 90s on cross-matching optical catalogues with catalogues of X-ray emitting sources. The main reason for doing this was to figure out which object was responsible for the X-ray ...
- 118k
2
votes
How to use Astropy to edit a keyword (not value) in batches of FITS file headers to be used in AstroimageJ (AIJ)? (summer undergrad research project)
This code snippet should do what you want for an individual fits file. It searches for the HDU containing 'DATE-BEG' and then writes a header 'DATE-OBS' containing the value of 'DATE-BEG'. You can use ...
- 21
1
vote
What are the applications of cross matching astronomical catalogues?
If I’m understanding what you’re asking, then it boils down to two things: resource management and different physics.
Let’s say you’re looking at a given variable star. Maybe you just started ...
- 2,647
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