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Originally Posted by orestis
This is very interesting stuff,just wondering how do they determine which is the primary and secondary components?
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Orestis,
For any double star, the primary is the brighter of the two stars. The apparent brightness of the stars will depend on their luminosity and distance. Generally, for a main sequence star luminosity is proportional to mass i.e. the larger the mass the higher the luminosity and the hotter the star. However, if a double star is a chance alignment, it is possible that the secondary is inherently more massive and luminous but appears less bright because it is much further way.
In the case of binary systems, the two stars are essentially the same distance from the Earth. If they are both main sequence stars then the brighter and more luminous star should also be the most massive. However, with these extremely close binaries I guess the stars are not "normal" and involve mass transfers and accretion disks etc. Thus, in the beta Lyrae system, the more luminous primary is less massive.
Regards, Rob