Beta Lyrae

Beta Lyrae

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
Distance960 ± 50 ly
(290 ± 10 pc)
Absolute magnitude (MV)−3.91
Absolute bolometric
magnitude (Mbol)		–6.3 ± 0.2 / –4.7 ± 0.1[7]
Orbit[2]
CompanionBeta 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
Mass13.16 ± 0.3 M☉
Radius6.0 ± 0.2 R☉
Luminosity26,300 L☉
Surface gravity (log g)4.0 ± 0.1 cgs
Temperature30,000 ± 2,000 K
β Lyr B
Mass2.97 ± 0.2 M☉
Radius15.2 ± 0.2 R☉
Luminosity6,500 L☉
Surface gravity (log g)2.5 ± 0.1 cgs
Temperature13,300 K
Age23 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
SIMBADdata

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

Etymology

Beta Lyrae has the traditional name Sheliak (occasionally Shelyak or Shiliak),[8] derived from الشلياق šiliyāq or Al Shilyāk, the Arabic name of the constellation of Lyra. The meaning of the name Sheliak is debated. It has been suggested to derive from السلحفاة al-sulḥafāt, the Arabic word for "tortoise." This, however, is likely an error related to a fellow star in Lyra: Sulafat.[10][11] Sheliak has also been linked to the meaning "eagle." Again, this is likely due to another star in the same constellation, Vega. Its name has been linked to the Arabic word wāqi‘, meaning "falling" or "landing", via the phrase an-nasr al-wāqi‘, "the falling eagle".[12] It is possible the name Sheliak is of non-Arabic origin, as it has no other meaning in Arabic and cannot be identified with an Arabic triliteral root.[13]

In China, the star was named Tsan Tae.,[11] from 漸台 (Jiāntāi), meaning Clepsydra Terrace, refers to an asterism consisting of this star, δ2 Lyrae, γ Lyrae and ι Lyrae.[14] Consequently, β Lyrae itself is known as 漸台二 (Jiāntāièr, English: the Second Star of Clepsydra Terrace.)

The Bayer designation for this star was given by the German astronomer Johann Bayer with the publication of his star atlas Uranometria in 1603. It was given the Flamsteed designation 10 Lyrae by John Flamsteed in 1712 with the first publication of his star catalogue. The variable luminosity of this system was discovered in 1784 by the British amateur astronomer John Goodricke.[15]

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 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[16] and the Michigan InfraRed Combiner (MIRC)[17] 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.[18]

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. β Lyr C is magnitude 9.9v separation 86" and with a luminosity 7 times that of the Sun. The Washington Double Star Catalog lists three more faint companions at one to two arc minutes separation.[19]

See also

Notes

  1. 1 2 3 4 5 van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. 1 2 3 4 5 6 Zhao, M.; et al. (September 2008), "First Resolved Images of the Eclipsing and Interacting Binary β Lyrae", The Astrophysical Journal 684 (2): L95–L98, arXiv:0808.0932, Bibcode:2008ApJ...684L..95Z, doi:10.1086/592146.
  3. 1 2 Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/gcvs. Originally published in: 2009yCat....102025S 1. Bibcode:2009yCat....102025S.
  4. ↑ Grzenia, B. J.; Tycner, C.; Jones, C. E.; Rinehart, S. A.; Van Belle, G. T.; Sigut, T. A. A. (2013). "Modeling Circumstellar Disks of B-type Stars with Observations from the Palomar Testbed Interferometer". The Astronomical Journal 145 (5): 141. Bibcode:2013AJ....145..141G. doi:10.1088/0004-6256/145/5/141.
  5. 1 2 Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Observatory, Bibcode:1978ppch.book.....N.
  6. ↑ Wilson, Ralph Elmer (1953), "General catalogue of stellar radial velocities", Washington (Carnegie Institution of Washington), Bibcode:1953QB901.W495......
  7. 1 2 Mennickent, R. E.; et al. (2006), "On the accretion disc and evolutionary stage of β Lyrae", Monthly Notices of the Royal Astronomical Society 432 (1): 799–809, arXiv:1303.5812, Bibcode:2013MNRAS.432..799M, doi:10.1093/mnras/stt515.
  8. 1 2 Allen, Richard Hinckley (1899), "Star-names and their meanings", New York (G. E. Stechert): 287, Bibcode:1899sntm.book.....A.
  9. ↑ "V* bet Lyr -- Eclipsing binary of beta Lyr type", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2011-12-20.
  10. ↑ http://stars.astro.illinois.edu/sow/sulafat.html
  11. 1 2 http://www.constellationsofwords.com/stars/Sheliak.html [Star Names, Their Lore and Meaning, Richard Hinckley Allen, 1889].
  12. ↑ https://books.google.com/books?id=szgnwKRanHEC&pg=PA55&lpg=PA55&dq=sheliak+meaning+arabic+star&source=bl&ots=sa57hfTAG-&sig=_DhwI7YPnSff3p5NsSSRoK8_q0o&hl=en&sa=X&ved=0CEkQ6AEwCGoVChMIo5288pSaxwIVFjaICh03_AAo#v=onepage&q=sheliak%20meaning%20arabic%20star&f=false
  13. ↑ Edward William Lane, Arabic-English Lexicon
  14. ↑ (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 3 日
  15. ↑ Hoskin, M. (1979), "Goodricke, Pigott and the Quest for Variable Stars", Journal for the History of Astronomy 10: 23–41, Bibcode:1979JHA....10...23H.
  16. ↑ ten Brummelaar, Theo; et al. (July 2005), "First Results from the CHARA Array. II. A Description of the Instrument", The Astrophysical Journal 628 (453): 453, arXiv:astro-ph/0504082, Bibcode:2005ApJ...628..453T, doi:10.1086/430729.
  17. ↑ Monnier, John D.; et al. (2006), "Michigan Infrared Combiner (MIRC): commissioning results at the CHARA Array", Proceedings of the SPIE, Advances in Stellar Interferometry 6268 (62681P): 62681P, Bibcode:2006SPIE.6268E..55M, doi:10.1117/12.671982.
  18. ↑ Carrier, F.; Burki, G.; Burnet, M. (2002). "Search for duplicity in periodic variable Be stars". Astronomy and Astrophysics 385 (2): 488. Bibcode:2002A&A...385..488C. doi:10.1051/0004-6361:20020174.
  19. ↑ Mason, Brian D.; Wycoff, Gary L.; Hartkopf, William I.; Douglass, Geoffrey G.; Worley, Charles E. (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466. Bibcode:2001AJ....122.3466M. doi:10.1086/323920.

External links

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