Light Curves
The light curves of beta Lyrae variables are quite smooth: eclipses start and end so gradually that the exact moments are impossible to tell. This is because the flow of mass between the components is so large that it envelopes the whole system in a common atmosphere. The amplitude of the brightness variations is in most cases less than one magnitude; the largest amplitude known is 2.3 magnitudes (V480 Lyrae).
The period of the brightness variations is very regular. It is determined by the revolution period of the binary, the time it takes for the two components to once orbit around each other. These periods are short, typically one or a few days. The shortest known period is 0.29 days (QY Hydrae); the longest is 198.5 days (W Crucis). In beta Lyrae systems with periods longer than 100 days one of the components generally is a supergiant.
Beta Lyrae systems are sometimes considered to be a subtype of the Algol variables; however, their light curves are different (the eclipses of Algol variables are much more sharply defined). On the other hand, beta Lyrae variables look a bit like W Ursae Majoris variables; however, the latter are in general yet closer binaries (so-called contact binaries), and their component stars are mostly lighter than the beta Lyrae system components (about one solar mass).
Read more about this topic: Beta Lyrae Variable
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