# Questions tagged [variable-star]

Questions regarding stars that undergo changes in their spectra, temperature, or luminosity.

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### How do you tell if a variable star is periodic or not by its light curve?

I have light curves for a particular star. I'm able to construct a periodogram of the stars' light curve, a plot of the power of the light curve vs. the signal's period. For a nonperiodic but ...
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1 vote
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### What is an actual value for the Eddington pulsation constant?

What numerical value does the pulsation constant $Q$ take in the formula that Eddington derived for variable stars: $$P\sqrt{\rho} = Q,$$ where $\rho$ — average star density, $P$ — period?
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### Lightcurve Labels

I had a query regarding light curve labels. As simple as it goes we can plot time (MJD, BJD, etc) on X-axis. Also, I know we can plot magnitudes on Y-axis. Again I've seen papers showing Relative flux ...
1 vote
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### What is the period of Gamma Cassiopeiae?

Gamma Cassiopeiae is a variable star whose magnitude changes between 1.6 and 3. On what timescale does it vary? The Wikipedia page says that it is irregular, but what is the timescale of its ...
• 16.7k
1 vote
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### What is the unit for durations on the AAVSO website?

The AAVSO website has a page for observers with binoculars. On this page, there is a table with stars of interest, and the period of each variable is indicated. However, the unit for the period is not....
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### Be stars - short variations

The origin of short-times variations in the brightness of Be stars is not clear. Some researchers consider them a consequence of non-radial pulsations. Some researchers consider them a consequence of ...
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### Spurious periods of stars

What exactly is meant by spurious periods of stars? E. Tanner writes in Spurious Periods in Spectroscopic Binaries in 1948 Furthermore: Can spurious periods be produced by aliasing, and how can they ...
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### What is the theoretical maximum variability a pulsating red giant can have such that a habitable planet can stay habitable for long periods of time?

I was reading about red giants and came across this statement: Some research suggests that, during the evolution of a 1 M☉ star along the red-giant branch, it could harbor a habitable zone for ...
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### Frequency analysis on Semiperiodic object(s) using Lomb-Scargle

So I already did a frequency analysis of the SRv-type's light curve using Period04. I already have the 'periodicities' of the object/star of choice which is quite hard since the latter/other periods ...
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### Why do the pulsations of a Cepheid variable occur?

I understand the theory of the mechanism by which Cepheid variables pulsate, where helium is ionised and deionised, leading to changes in diameter. However, I am unsure if the brightness changes due ...
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### Calibrating raw photometric measurements

So I have a photometry data sourced from Solar Mass Ejection Imager's (SMEI) server as an ‘add-on data’ for my point source of interest (a variable star) with a 104 minute cadence. However, it’s not ...
• 105
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### Delta Velorum - non-observed variable star

I am a beginner variable star observer from the Southern Hemisphere (but with experience in astronomy) and, when I was looking for VS to observe, I saw that Del Vel has almost no observations. Thus, ...
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### How do you correct the Period-Luminosity relationship for metallicity?

Refer to the link: https://www.astro.utoronto.ca/DDO/research/cepheids/cepheids.html Tha author has used the relationship $M_V=-2.902log(P)-1.203$. It is mentioned that this is not corrected for ...
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### How is V1057 Cygni supposed to go from K type dwarf to F type giant?

FU Orionis variables are protostars that go through massive outbursts that drastically change the star's spectral type and magnitude. With the star V1057 Cygni, this star was known to go from a K type ...
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### Is Betelgeuse is continually expelling material on the scale of the 2019/2020 event?

The AUGUST 13, 2020 Phys.org article Results from Hubble suggest that Betelgeuse's recent dimming was due to material ejected from the star says: ...the star's unexpected and significant dimming ...
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1 vote
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### Why does the Gaia color-magnitude diagram have this shape?

I was looking at the visualization tools of Gaia, and tried plotting a color-magnitude diagram. On the right hand side of the image, photGMeanMag (mag) (the amount ...
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### How variable does a star have to be, to be a variable star?

Variable stars are stars whose apparent magnitude varies. But there are so many phenomena that can cause a star to be variable, that I would expect all stars to be variable. A rotating star has a ...
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### Color index B-V of the dimming Betelgeuse

Using AAVSO light curve generator I have plotted V and B magnitudes of Betelgeuse in the past 150 days to see trend of B-V color index. If dust would be the cause of the recent drop in the star ...
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### What are these data in light curve generator

I'm generating light curves for some variable stars on the AAVSO website (see https://www.aavso.org/lcg ) . I can choose what type of data must be plotted. Can you explain what they are? Thank you in ...
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### Are stars expected to become dimmer before a supernova?

With the recent news about the "fainting" of Betelgeuse and the speculation that this might be a precursor to a supernova, I'm wondering if there is any theoretical/observational basis for this ...
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### When we say a variable star is "fainting" does it mean something more or different than "dimming" or "fading"?

A comment below the question Does the current “fainting” of Betelgeuse show any spectral trends that differ from it's normal variability? suggests that "dimming" would be a better term, but I have a ...
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### Does the current "fainting" of Betelgeuse show any spectral trends that differ from it's normal variability?

update: With all the newest news about including what the Dr. Becky video discusses as linked in How do magnetic fields mess with astronomers' observations? I'll bet this question can now be ...
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1 vote
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### Why do these photometric observations of Betelgeuse look "quantized" in 0.1 magnitude steps?

The most interesting question related to this Will Kinney tweet would be what's going on with Betelgeuse? but I can't help but wonder why much but not all of the photometric data is clustered in ...
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### Astrophysics of Supernovae - Energy over Distance?

I need this for worldbuilding, but it is a physics question. I want to be able calculate the energy over distance from a hypernova of a variable star like Eta Carinae. Understanding what energy levels ...
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### Brown dwarf magnetic activity

I have not been able to find an answer to my question through google, and therefore ask it on this medium. Do brown dwarfs have spots and faculae similar to other heavier stars?
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### Large amplitude dipole pulsator

Consider a semiregular variable with amplitude of 1.5 mag. Is it possible to explain brightness variations by purely dipole pulsations?
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### What is period doubling in a variable star?

I'm coming across the concept of "period doubling" in RR Lyrae stars. When I look up what period doubling is on the Internet, I find general-level explanations of bifurcations of dynamical systems ...
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### Are stars beyond the asteroid belt less constant?

If we graph the variability of a small bright star which is lined up with the asteroid belt, is it less constant than stars that are far away from the asteroid belt? To what degree does variability ...
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### Stopping down a telescope to reduce brightness by 5 magnitudes

Suppose we have a variable star with a change in magnitude between maximum and minimum of 5 mag. How much would you need to stop down a telescope (block some of the area) so that the star at maximum ...
283 views

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

I understand that the kappa mechanism (that leads to star variability) causes an increase of opacity with increasing temperature in partial ionization zones. However, I'm not sure I understand what ...
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1 vote
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### Do stars vary their own brightness?

All I could find on the internet was about how stars vary in brightness depending on their distance to Earth, temperature, type of star... But my question is, can a star can change its brightness.
1 vote