# Tag Info

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
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### 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
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### 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
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### 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

### 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 ...
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### 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

### 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
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### 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 ...

### 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
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### 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
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### 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
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### 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
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### 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

### 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
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### 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
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### 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

### 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/?...
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### 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 ...
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### 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
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### 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
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### 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
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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 ...
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### 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

### 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
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
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

### 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 ...
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### 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