Sat, 03/26/2022 - 19:59
Hey everybody,
To figure out the amplitude of the fundamental period (P0) of a pulsating variable star is apparently pretty straight forward, but how can we figure out the amplitude of the first overtone (P1) of, lets say, a double mode pulsating star? Is there a way to do get this figure out of VStar? I guess it has something to do to make a phase graph of the residuals after the data whitening, but not sure how this is achieved.
Thanks in advance!
Clear and dark skies!
Hi Enrique
Working through an example here may be best. Can you provide/suggest an example dataset, e.g. from AID?
David
Hello, David.
Thanks for your prompt reply! Yes, sure, this is specifically for AS Cas, which through AAVSOnet (BSM) have been achieved a bunch of observations during the past two years.
Best regards,
Enrique
Hi Enrique,
I have some experience with this problem.
When you run the frequence fourier tranform you see the main mode if your data set is big enough. You may see plenty of alias peaks if you have gaps between data, what is always the case for short term pulsators. Pick the main frequency (which is ideally the one in the middle of the alias peaks, but sometimes that's not necessarily the case) and create a model with the main frequency and a few harmonics. Then run the fourier analysis again for the residuals, not the actual measurement data. This porcess is called pre-whitening amd you will get is a power spectrum which should show the overtone (maybe again with alias peaks). The alias peaks of the fundamental mode will dissapear with the mode frequency itself. You can now build a model with both fundamental and overtone and run again the fft on the remaining residuals. This may show you another frequncy which can be another overtone or a combination frequency. Or you see only noise (whciih may disclose other smal amplitude frequncies).
Hope that helps,
Matthias
Vielen dank, Matthias!
So, what you're suggesting is that instead of the DC DFT with Period Range that I was performing, I should use the DC DFT with Frequency Range to find out the amplitude of the 1st overtone, right?
I will try that then.
Viele Grüsse!
Enrique