# 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 ...
• 33.8k
Accepted

### 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 ...
• 14.7k
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 ...
• 115k
Accepted

### 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 ...
• 33.8k
Accepted

### 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 ...
• 14.4k

### 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 ...
• 88.7k

### 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 ...
• 4,961

### 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 ...
• 5,142

### 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 ...
• 1,335
Accepted

### 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 ...
• 88.7k

### 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 ...
• 121
Accepted

### 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 ...
• 5,294

### 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 ...

### 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 ...
• 88.7k

### 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.
• 115k
Accepted

### 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{\...
• 1,680

### What is the period of Gamma Cassiopeiae?

The variation isn't periodic. The light curve below (from aavso) shows the period from 1960. In the 1930s the star also had an episode of fading and brightening, It faded by about a magnitude over ...
• 88.7k

### Be stars - short variations

Learning how to tactfully and strategically read/skim/scan through many papers to find the bits of information or other papers that you're looking for (and leaving a more in-depth examination for ...
• 3,819
1 vote
Accepted

### Frequency analysis on Semiperiodic object(s) using Lomb-Scargle

This is a partial answer based on the discussion in comments below the question. If one already has an "amplitude spectrum" and one wants to convert to a power spectrum, all you have to do ...
• 31.5k
1 vote
Accepted

### What is the unit for durations on the AAVSO website?

Based on a few stars that I recognize (omicron Ceti, R Aqr) the period is in units of days. The period for these types of stars is often on the order of one year. The precision is misleading. I assume ...
• 7,085
1 vote
Accepted

### What are these data in light curve generator

The file format for submitting observations to AAVSO sheds some light on this. "Visual" data are estimates by visual comparison to nearby reference stars of similar brightness. U, B, V, R, I data ...
• 16.5k
1 vote

### Astrophysics of Supernovae - Energy over Distance?

In short, there are no nice standard formulas for this. One can make some order-of-magnitude calculations, though. The key formula you need is the inverse-square law: the intensity of a spherical ...
• 10.3k
1 vote

### Stopping down a telescope to reduce brightness by 5 magnitudes

Treating as a school question Each change of 1 magnitude changes brightness by how much? So by what factor will a change of 5 magnitudes give? (5 magnitudes is a very convenient number for this ...
• 88.7k
1 vote
Accepted

### What leads to increase in opacity in kappa mechanism?

It's a bit subtle, the key thing the partial ionization does is to keep the temperature from changing much. What you really want is an increase in density, not temperature. The reason the kappa ...
• 5,142

Only top scored, non community-wiki answers of a minimum length are eligible