|Binary system Beta Lyrae|
Astronomical artist © Fahad Sulehria
image Encyclopedia of Science
Beta Lyrae (β Lyr, β Lyrae) is a binary star system approximately 960 light-years away in the constellation Lyra. The traditional name is Sheliak derived from الشلياق šiliyāq or Al Shilyāk, the Arabic name of the constellation of Lyra.***
The Bayer designation for this star was given by the German lawyer and uranographer (celestial cartographer) Johann Bayer (1572 – 1625) with the publication of his star atlas Uranometria Omnium Asterismorum in 1603.
|John Flamsteed in 1702|
|John Goodricke about 1785|
Semidetached binary system
Beta Lyrae is a semidetached binary system made up of a stellar class B7II primary star and a secondary that is probably also a B-type star.
B-type stars are very luminous and blue. Their spectra have neutral helium, which are most prominent at the B2 subclass, and moderate hydrogen lines. As O- and B-type stars are so energetic, they only live for a relatively short time. Thus, due to the low probability of kinematic interaction during their lifetime, they do not, and are unable to, stray far from the area in which they were formed, apart from runaway stars.
The fainter, less massive star (B7II) in the system was once the more massive member of the pair, which caused it to evolve away from the main sequence first and become a giant star. Because the pair are in a close orbit, as this star expanded into a giant it filled its Roche lobe and transferred most of its mass over to its companion.
The secondary, now more massive star is surrounded by an accretion disk from this mass transfer, with bipolar, jet-like features projecting perpendicular to the disk. This accretion disk blocks our view of the secondary star, lowering its apparent luminosity and making it difficult for astronomers to pinpoint what its stellar type is.
The amount of mass being transferred between the two stars is about 2 × 10−5 solar masses per year, or the equivalent of the Sun's mass every 50,000 years, which results in an increase in orbital period of about 19 seconds each year
|CHARA One of the six telescopes that are part of the interferometer|
"CHARA 1497" by Davefoc - Own work.
Licensed under CC BY-SA 3.0 via Commons
The orbital plane of this system is nearly aligned with the line of sight from the Earth, so the two stars periodically eclipse each other. This causes Beta Lyrae to regularly change its apparent magnitude from +3.4 to +4.6 over an orbital period of 12.9414 days.
The two components are so close together that they cannot be resolved with optical telescopes, forming a spectroscopic binary.
In 2008, the primary star and the accretion disk of the secondary star were resolved and imaged using the CHARA Array interferometer at Georgia State University and the Michigan InfraRed Combiner (MIRC) in the near infrared H band, allowing the orbital elements to be computed for the first time.
Michigan InfraRed Combiner (MIRC) is a near-infrared image-plane combiner at the CHARA array which consists of six 1-m diameter telescopes with the longest baseline of 330m. MIRC was upgraded from a 4-beam to a full 6-beam combiner in July 2011, which now records interferometry data of 15 baselines and 20 triangles simultaneously.
The improved snapshot UV coverage has greatly boosted the ability for imaging complicated targets such as the asymmetry of circumstellar disks, interacting binaries and the surfaces of spotted stars.
In addition, the Photometric Channels subsystem, which directly measures the real time flux of individual beams, has been upgraded to increase the light throughput to improve the visibility and closure phase calibration.
The system sensitivity has been improved as well to allow fainter objects such as Young Stellar Objects (YSOs) to be observable with MIRC for the first time. Our presentation will conclude with first preliminary results of imaging two Be binaries observed by the upgraded MIRC.
SAO/NASA ADS Astronomy Abstract Service
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