Beta Lyrae

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Beta Lyrae
Lyra constellation map.svg

Location of β Lyrae in Lyra
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Lyra
Right ascension 18h 50m 04.79525s[1]
Declination +33° 21′ 45.6100″[1]
Apparent magnitude (V) 3.52[2] (3.25 – 4.36[3])
Characteristics
Spectral type B7Ve[4] + B[2]
U−B color index −0.56[5]
B−V color index +0.00[5]
Variable type β Lyr[3]
Astrometry
Radial velocity (Rv) −19.2[6] km/s
Proper motion (μ) RA: 1.90[1] mas/yr
Dec.: −3.53[1] mas/yr
Parallax (π) 3.39 ± 0.17[1] mas
Distance 960 ± 50 ly
(290 ± 10 pc)
Absolute magnitude (MV) −3.91[citation needed]
Absolute bolometric
magnitude (Mbol)		 –6.3 ± 0.2 / –4.7 ± 0.1[7]
Orbit[2]
Companion Beta Lyrae B
Period (P) 12.9414 days
Semi-major axis (a) 0.865 ± 0.048"
Eccentricity (e) 0
Inclination (i) 92.25 ± 0.82°
Longitude of the node (Ω) 254.39 ± 0.83°
Details[7]
β Lyr A
Mass 13.16 ± 0.3 M☉
Radius 6.0 ± 0.2 R☉
Luminosity 26,300 L☉
Surface gravity (log g) 4.0 ± 0.1 cgs
Temperature 30,000 ± 2,000 K
β Lyr B
Mass 2.97 ± 0.2 M☉
Radius 15.2 ± 0.2 R☉
Luminosity 6,500 L☉
Surface gravity (log g) 2.5 ± 0.1 cgs
Temperature 13,300 K
Age 23 Myr
Other designations
Sheliak, Shelyak, Shiliak, [8] 10 Lyrae, AAVSO 1846+33, BD+33°3223, FK5 705, HD 174638, HIP 92420, HR 7106, SAO 67451.[9]
Database references
SIMBAD data

Beta Lyrae (β Lyr, β Lyrae) is a binary star system approximately 960 light-years (290 parsecs) away in the constellation Lyra.

Names

The Bayer designation for this star, Beta Lyrae, is due to Johann Bayer's Uranometria of 1603. It was given the Flamsteed designation 10 Lyrae by John Flamsteed in 1712 with the first publication of his star catalogue.

Beta Lyrae has the alternative name Sheliak (occasionally Shelyak or Shiliak), derived from الشلياق šiliyāq or Al Shilyāk, one of the Arabic names of the constellation of Lyra.[8]

In Chinese astronomy, Tsan Tae (漸台 (Jiāntāi), meaning Clepsydra Terrace, refers to an asterism consisting of this star, δ2 Lyrae, γ Lyrae and ι Lyrae.[10] Consequently, β Lyrae itself is known as 漸台二 (Jiāntāièr, English: the Second Star of Clepsydra Terrace.)


Properties

Beta Lyrae is a semidetached binary system made up of a stellar class B7 main sequence primary star and a secondary that is probably also a B-type star. The fainter, less massive star 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.[2] 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. The spectrum of Beta Lyrae shows emission lines produced by the accretion disc. The disc produces around 20% of the brightness of the system.[2]

Variability

The variable luminosity of this system was discovered in 1784 by the British amateur astronomer John Goodricke.[11] 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 +3.2 to +4.4 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[12] and the Michigan InfraRed Combiner (MIRC)[13] in the near infrared H band (see video below), allowing the orbital elements to be computed for the first time.[2]

In addition to the regular eclipses, the system shows smaller and slower variations in brightness. These are thought to be caused by changes in the accretion disc and are accompanied by variation in the profile and strength of spectral lines, particularly the emission lines. The variations are not regular but have been characterised with a period of 282 days.[14]

Companions

In addition to the spectroscopic pair, several other companions to Beta Lyrae have been catalogued. β Lyr B, at an angular distance of 45.7", is of spectral type B7 V, has an apparent magnitude of +7.2, and can easily be seen with binoculars. It is about 80 times as luminous as the Sun and is also a spectroscopic binary with a period of 4.34 days.[citation needed] β Lyr C is magnitude 9.9v separation 86" and with a luminosity 7 times that of the Sun.[citation needed] The Washington Double Star Catalog lists three more faint companions at one to two arc minutes separation.[15]

See also

Notes

  1. ↑ 1.0 1.1 1.2 1.3 1.4 Lua error in package.lua at line 80: module 'strict' not found.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 2.5 Lua error in package.lua at line 80: module 'strict' not found.
  3. ↑ 3.0 3.1 Lua error in package.lua at line 80: module 'strict' not found.
  4. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  5. ↑ 5.0 5.1 Lua error in package.lua at line 80: module 'strict' not found.
  6. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  7. ↑ 7.0 7.1 Lua error in package.lua at line 80: module 'strict' not found.
  8. ↑ 8.0 8.1 "Sheliak, Shelyak, and Shiliak are from Al Shilyāk, one of the Arabian names for Lyra" Lua error in package.lua at line 80: module 'strict' not found.
  9. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  10. ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
  11. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  12. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  13. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  14. ↑ Lua error in package.lua at line 80: module 'strict' not found.
  15. ↑ Lua error in package.lua at line 80: module 'strict' not found.

External links

  • Lua error in package.lua at line 80: module 'strict' not found.
  • Philippe Stee's homepage: Hot and Active Stars Research
  • Lua error in package.lua at line 80: module 'strict' not found.
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