Friday, November 13, 2015

Lyra - V361 Lyrae a contact binary

Contact binary
Image David Darling, The Internet Encyclopedia of Science 
V361 Lyrae is a faint star at the very northernmost edge of the constellation. It can be found less than a degree away from the naked-eye star 16 Lyrae,

V361 us a 5th-magnitude A-type subgiant located around 120.6 ly (37 parsecs) distant. It is an eclipsing binary that does not easily fall into one of the traditional classes, with features of Beta Lyrae, W Ursae Majoris, and cataclysmic variables.

It may be a representative of a very brief phase in which the system is transitioning into a contact binary.

Contact binaries
Contact binary is a binary star system whose component stars are so close that they touch each other or have merged to share their gaseous envelopes.

A binary system whose stars share an envelope may also be called an overcontact binary.

Almost all known contact binary systems are eclipsing binaries; eclipsing contact binaries are known as W Ursae Majoris variables, after their type star, W Ursae Majoris.

Contact binaries are sometimes confused with common envelopes. However, whereas the configuration of two touching stars in a contact binary has a typical lifetime of millions to billions of years, the common envelope is a dynamically unstable phase in binary evolution that either expels the stellar envelope or merges the binary in a timescale of months to years.

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