# Tag Info

21

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 immediately preceding a supernova. There are several mechanisms that could lead to this sort of mass loss (see slides 24-25), including gravity-wave driven ...

4

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 categories: Pulsating stars, where fluctuations lead to increases and decreases in size or temperature, which in turn produce changes in the star's brightness. ...

3

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 star-like behaviours, but are in fact much closer to planets (due to them being below critical mass for hydrogen fusion in their cores) All planets that ...

3

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 observational meaning, which happens when you have a clear periodic pulsation in a star, but the amplitude shows a higher-lower-higher-lower pattern that implies a "...

3

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 measured to have such small variations that they are recorded as "standard" stars and for most purposes can be considered to have a constant brightness and thus be ...

3

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 average luminosity (and so their average absolute magnitude). This graph relates the period to their average absolute magnitude. To use the graph, observe a cepheid ...

3

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 that the conventions you seem to be referencing don't come from Hipparcos at all. Likely you're seeing the names of these stars as they're referred to by some ...

3

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 true star (check out the Hertzsprung Russell diagram showing stellar evolution) later in its life, depending mainly on its mass it can either evolve into a ...

3

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 general catalogue of variable stars lists stars like Alpha Triangulum, with a variability of 0.01 magnitudes. Ultimately a variable star is a star which has had ...

2

The diagram you've plotted is a color-magnitude diagram, and the magnitude it plots is the apparent magnitude. If you click the Plot2D button and select the plot type, under "Astrophysical parameters" you will find "GDR2 HR diagram". This produces a plot that looks like this: This is probably somewhat closer to what you are expecting. It isn't the same ...

2

Try plotting absolute G magnitude (i.e. corrected for the fact tthat all the stars are at different distances) on the y-axis.

1

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 come from CCD cameras using standard filters in the Johnson-Cousins photometric system, with passbands ranging from near ultraviolet to near infrared. The J and H ...

1

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 energy source falls off with the inverse square of distance. $$I(r)=\frac{I}{r^2}.$$ The useful thing is that if you know that some source with intensity $I_1$ ...

1

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 question) You will need to reduce the area of the telescope by the same factor.

1

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 mechanism is important is that it allows heat to be added to the gas when it is compressed, and removed when the gas is expanded, that's what allows for the ...

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