Astronomy:Eta Lyrae

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Eta Lyrae
Observation data
Equinox J2000.0]] (ICRS)
Constellation Lyra
Right ascension  19h 13m 45.48832s[1]
Declination +39° 08′ 45.4801″[1]
Apparent magnitude (V) 4.43[2]
Characteristics
Spectral type B2.5IV[3]
B−V color index −0.150±0.002[2]
Astrometry
Radial velocity (Rv)−8.1±0.9[1] km/s
Proper motion (μ) RA: −0.60[1] mas/yr
Dec.: −1.26[1] mas/yr
Parallax (π)2.35 ± 0.13[1] mas
Distance1,390 ± 80 ly
(430 ± 20 pc)
Absolute magnitude (MV)−3.71[2]
Orbit[4]
Period (P)56.4±0.5 d
Semi-major axis (a)≥ 1.841 Gm (0.01231 astronomical unit|AU)
Eccentricity (e)0.53±0.12
Periastron epoch (T)2,441,868.4±3.4 JD
Argument of periastron (ω)
(secondary)		337±28°
Semi-amplitude (K1)
(primary)		2.8±0.5 km/s
Details
Mass9.97±0.98 M☉[5]
10.1±1.0[6] M☉
Radius4.3[7] R☉
Luminosity6,605[2] L☉
Luminosity (bolometric)19,095[5] L☉
Surface gravity (log g)3.38[8] cgs
Temperature17,360 K[8]
19,525[5] K
Metallicity [Fe/H]−0.01[8] dex
Rotational velocity (v sin i)10[9] km/s
Age22.5±2.6[6] Myr
Other designations
Eta Lyr or η Lyr, 20 Lyr, BD+38°3490, HD 180163, HIP 94481, HR 7298, SAO 68010, WDS 19138+3909[10]
Database references
SIMBADdata

Eta Lyrae, a name Latinized from η Lyrae, is a likely binary star[11] system in the northern constellation of Lyra. It has the traditional name Aladfar /əˈlædfɑːr/ and is faintly visible to the naked eye with an apparent visual magnitude of 4.43.[2] The system is located at a distance of approximately 1,390 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −8 km/s.[1]

Nomenclature

η Lyrae (Latinised to Eta Lyrae) is the binary star's Bayer designation. Its designation as the A component of a double star, and of its two constituents as the Aa and Ab components, derives from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[12]

'BD +38 3491' is the 'B' component's designation in the Bonner Durchmusterung astrometric star catalogue.

Eta Lyrae bore the traditional name Aladfar, from the Arabic الأظفر al-ʼuẓfur "the talons (of the swooping eagle)", a name it shares with Mu Lyrae (though the latter is typically spelled Alathfar).[13] The Working Group on Star Names (WGSN)[14] has approved the name Aladfar for the Aa component of the system (the primary component of Eta Lyrae).[15]

Properties

The suspected radial velocity variations of this star in 1938 led to it being incorrectly classified as a Beta Cephei-type star, although there was some early disagreement about the variation.[16] In 1951, J. A. Pearce and R. M. Petrie also noted that the star appeared to have a variable radial velocity.[17] It was announced as a binary system by H. A. Abt and S. G. Levy in 1978, who listed it as a single-lined spectroscopic binary, albeit with marginal elements. The putative components have an orbital period of 56 days with an eccentricity (ovalness) of 0.5 and a small radial velocity variation of 2.8 km/s.[4]

The visible component of this system is a massive B-type star with a stellar classification of B2.5IV.[3] It is around 23[6] million years old with ten[6] times the mass of the Sun and a low rotational velocity. The star is radiating around 19,525 times the luminosity of the Sun from its photosphere at an effective temperature of 19,525 K.[5] A magnetic field has been detected with an average quadratic field strength of (169.0±115.9)×10−4 T.[18]

The magnitude 8.58 star BD +38 3491 forms a visual companion to this pair. It is designated Eta Lyrae B in the Washington Double Star Catalog, and is located at an angular separation of 28.40 arcseconds along a position angle of 81°, as of 2017.[19]

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 van Leeuwen, F. (November 2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V. 
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Anderson, E.; Francis, Ch. (2012). "XHIP: An extended hipparcos compilation". Astronomy Letters 38 (5): 331. doi:10.1134/S1063773712050015. Bibcode: 2012AstL...38..331A. 
  3. ↑ 3.0 3.1 Lesh, Janet Rountree (December 1968), "The Kinematics of the Gould Belt: an Expanding Group?", Astrophysical Journal Supplement 17: 371, doi:10.1086/190179, Bibcode: 1968ApJS...17..371L 
  4. ↑ 4.0 4.1 Abt, H. A.; Levy, S. G. (1978). "Binaries among B2-B5 IV, V absorption and emission stars". The Astrophysical Journal Supplement Series 36: 241. doi:10.1086/190498. Bibcode: 1978ApJS...36..241A. 
  5. ↑ 5.0 5.1 5.2 5.3 Hohle, M. M. et al. (April 2010). "Masses and luminosities of O- and B-type stars and red supergiants". Astronomische Nachrichten 331 (4): 349. doi:10.1002/asna.200911355. Bibcode: 2010AN....331..349H. 
  6. ↑ 6.0 6.1 6.2 6.3 Tetzlaff, N. et al. (January 2011). "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun". Monthly Notices of the Royal Astronomical Society 410 (1): 190–200. doi:10.1111/j.1365-2966.2010.17434.x. Bibcode: 2011MNRAS.410..190T. 
  7. ↑ Pasinetti Fracassini, L. E. et al. (2001). "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)". Astronomy & Astrophysics 367 (2): 521–24. doi:10.1051/0004-6361:20000451. Bibcode: 2001A&A...367..521P. 
  8. ↑ 8.0 8.1 8.2 Cenarro, A. J. et al. (2007). "Medium-resolution Isaac Newton Telescope library of empirical spectra - II. The stellar atmospheric parameters". Monthly Notices of the Royal Astronomical Society 374 (2): 664–690. doi:10.1111/j.1365-2966.2006.11196.x. Bibcode: 2007MNRAS.374..664C. 
  9. ↑ Prugniel, Ph. et al. (2011). "The atmospheric parameters and spectral interpolator for the MILES stars". Astronomy & Astrophysics 531: A165. doi:10.1051/0004-6361/201116769. Bibcode: 2011A&A...531A.165P. 
  10. ↑ "* eta Lyr". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=%2A+eta+Lyr. 
  11. ↑ Eggleton, P. P.; Tokovinin, A. A. (September 2008). "A catalogue of multiplicity among bright stellar systems". Monthly Notices of the Royal Astronomical Society 389 (2): 869–879. doi:10.1111/j.1365-2966.2008.13596.x. Bibcode: 2008MNRAS.389..869E. 
  12. ↑ Hessman, F. V.; et al. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
  13. ↑ Allen, Richard Hinckley (25 October 2018). Star-Names and Their Meanings. Creative Media Partners, LLC. ISBN 978-0-344-21405-9. https://books.google.com/books?id=TPJAvwEACAAJ. 
  14. ↑ "IAU Working Group on Star Names (WGSN)". https://www.iau.org/science/scientific_bodies/working_groups/280/. 
  15. ↑ "Naming Stars". IAU.org. https://www.iau.org/public/themes/naming_stars/. 
  16. ↑ Heard, J. F. (1949). "An Analysis of Radial-Velocity Measures of Eight Stars Formerly Assigned to the Beta Cephei Group". The Astrophysical Journal 109: 185. doi:10.1086/145122. Bibcode: 1949ApJ...109..185H. 
  17. ↑ Pearce, J. A.; Petrie, R. M. (1951). "Revised radial velocities of seventy-nine B-type stars". Publications of the Dominion Astrophysical Observatory Victoria 8: 409–427. Bibcode: 1951PDAO....8..409P. 
  18. ↑ Bychkov, V. D. et al. (August 2003). "Catalogue of averaged stellar effective magnetic fields. I. Chemically peculiar A and B type stars". Astronomy and Astrophysics 407 (2): 631–642. doi:10.1051/0004-6361:20030741. Bibcode: 2003A&A...407..631B. 
  19. ↑ Mason, B. D. et al. (2014). "The Washington Visual Double Star Catalog". The Astronomical Journal 122 (6): 3466–3471. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M. 



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