Wed, 08/16/2023 - 09:51
Hi all. A probably very basic question. In VSX there are ELLs with a large or very large period (ten or more days). How can these long periods be physically compatible with a pair of stars that must be close enough to cause the deformation of the star that produces the variation of the ELL? I was convinced that the only difference with the EW was the line of sight with no eclipse, but evidently this is not the case.
Thanks a lot.
Franco Travaglino
Hello,
This is a very insightful question. The truth is that from the standpoint of the light curve itself there isn't much difference. They can look almost identical. In most cases the ellipsoidal variation is significantly smaller because it's caused by distortion of the star, whereas EW is caused by one star blocking the light of the other. Since the EW stars are almost always the same size (which I'm not going to go into now) there is typically a half a magnitude or more dip. Distortion is typically a much smaller effect because it is hard to change the shape of a star. However, that is only true for main sequence stars. As a star ages it goes through a process of puffing up through the giant or supergiant phase depending on its initial mass. These stars as you may imagine are much easier to "distort" so the ellipsoidal variation can be much larger, even for longer period systems. If however, the spectral type is not a giant or supergiant, then it is possible it is misclassified. Hope this answers your question.
Thanks,
Thanks a lot. In fact, the subject that generated my doubt is on the ascending branch of the HR diagram. However a period of 38 days, as in my subject, should involve a considerable distance, I wonder what kind of companion could deform a red giant to cause an ELL variability.