# Tag Info

Accepted

### Are stars expected to become dimmer before a supernova?

The connection between the dimming and a putative supernova relies on the interpretation that the decrease in luminosity may be due to circumstellar material, ejected in the years/decades/centuries ...
• 37.3k
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### What does HJD-2450000 mean?

HJD is the "Heliocentric Julian Date" HJD-2450000 is HJD minus 2450000 The Julian day is the number of days since the start of 4713 BC, with 0 assigned to the day of Monday, January 1st 4713 ...
• 127k
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### Does the expansion and contraction of a variable star affect the measured radial velocity?

The radial velocity variations of beta Cep were discovered by Frost (1902) using a spectrograph with photographic plates. The amplitude of the variations was approximately what you have measured. ...
• 157k

### Intuitive connection between the periods of oscillation of Betelgeuse and the elemental concentrations at its core? (Betelgeuse; Saio et al. (2023))

Sensationalist stuff and the $10^1$ to $10^2$ years till supernova claim is not made by the authors. The radial pulsation frequencies of a ball of gas depend on mass and radius. For a given mass, the ...
• 157k
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### When we say a variable star is "fainting" does it mean something more or different than "dimming" or "fading"?

Saying a star is "fainting" is simply an error; the correct terminology is "dimming" or "fading". (I suspect it's a plausible mistake for non-native speakers if they know ...
• 17.9k

### How does one actually fold a light curve?

Assume I have a bunch of measurements of something like brightness or flux versus time, and I know or guess a period for these data. Pick a zeropoint in time - say the time of the first observation - ...
• 157k

### Does the expansion and contraction of a variable star affect the measured radial velocity?

Yes, though I'd not expect the values to vary around 0,but around $-10km/s$. For example see https://www.aavso.org/vsots_betacep
• 20.1k

### Delta Velorum - non-observed variable star

I am the discoverer of delta Velorum's variability (along with the Galileo spacecraft) and I detected those variations visually, so yes, they can be observed, and they are really fun! If you go to the ...
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### Do stars vary their own brightness?

They can, and some do. These stars are called variable stars, because their luminosities as observed from Earth vary over time, often (though not always) in a regular period. Here are some broad ...
• 37.3k
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### Variable Types of Stars

It seems to me that you're mostly asking about star naming conventions, which is unfortunately a difficult thing to master because there are many many conventions. What makes this process difficult is ...
• 15.1k
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### Other than Lomb-Scargle Periodograms and String Length Minimization, what other methods can be used to find the period of unevenly spaced data?

A common method is to use the autocorrelation function (ACF). A description of an application of this technique for finding the rotation periods of stars in Kepler data is given by McQuillan et al. (...
• 157k
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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 ...
• 157k
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### What are the twinkling stars in the New Horizons Arrokoth approach?

I got a still from the video and uploaded it to nova.astrometry.net. This successfully identified the field and provided an astrometrically calibrated image. The two stars are: The fainter, large ...
• 157k

### Period-Luminosity Relation of Cepheids via Gaia Data

Here is a similar plot I adapted from Clementini et al. (2019). It shows mean absolute Gaia G-magnitude (derived from Gaia-DR2 parallaxes) versus period for 998 known Cepheid variables. I guess that ...
• 157k
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### What element drives pulsations in T Tauri Stars?

T-Tauri stars are not pulsational variables. Their variability, on timescales of minutes to decades, is associated with: spots and magnetically active regions on their surfaces; with variability of ...
• 157k

### Calibrating raw photometric measurements

I have never worked with SMEI but I do have some experience with photometry and, while I do not understand completely the question, I think I can give you some ideas. First of all, did you get the ...
• 131
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### Calibrating raw photometric measurements

If I understand the question correctly, you have raw data from a CCD sensor in arbitray units (which correlate with brightness) and your challenge is to callibrate this intensity for a certain ...
• 5,636
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### How variable does a star have to be, to be a variable star?

There is no lower limit, and as you say, all stars are somewhat variable. However catalogues of variable stars exist, and they can record a wide range of levels of variability. For example, the ...
• 127k

### Do stars vary their own brightness?

Looking at the question longer-term, a star's brightness also changes as it evolves: starting possibly with some brightness of its initial accretion disc, then as nuclear burning begins it becomes a ...
• 151

### How to find a Cepheid's pulsation period using its graph?

This graph is not the light curve of a cepheid. It is used to find the average brightness of the star, and from that, estimate its distance. The rate at which cepheids pulse is related to their ...
• 127k

### Brown dwarf magnetic activity

So far, opinion is divided, as evidence has not been found to prove either way. Back in 2015, a study published in Nature, and linked via the Verge, here suggested that no, brown dwarfs do not exhibit ...
• 5,097

### What is period doubling in a variable star?

I think part of the confusion comes from the fact that "period doubling" can mean two rather different things, which are probably related but this is not completely known. The first is a purely ...
• 5,336

### Are stars beyond the asteroid belt less constant?

No, stars that are seen through the asteroid belt are not any more variable than stars in any other part of the sky. All stars vary in brightness on measurable timescales, although some have been ...
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### Delta Velorum - non-observed variable star

Yes it varies in the visible spectrum. The paper The nearby eclipsing stellar system δ Velorum describes why this is difficult target. Surprisingly it is because it is so bright. The absolute ...
• 127k
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### What determines how accurate a particular method is at finding the period between Lomb-Scargle and String Length Minimization?

I think they are just not the best period-finding algorithms. They are too simple. For high signal-to-nose data with SINGLE periods they seem to work ok, but the problem is always with low-quality ...

### Why does the Gaia color-magnitude diagram have this shape?

Try plotting absolute G magnitude (i.e. corrected for the fact tthat all the stars are at different distances) on the y-axis.
• 157k
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### What is an actual value for the Eddington pulsation constant?

This is an attempt to answer the question as to the value of the Eddington pulsation constant as it relates to Cepheid variables. The constant, $Q$, is defined as: Q = P\sqrt{\rho} = P\sqrt{\frac{\...
• 2,349