Mu Lyrae

μ Lyrae, Latinized as Mu Lyrae, is a solitary[8] star in the northern constellation Lyra. It has the traditional name Alathfar /əˈlæθfɑːr/, from the Arabic الأظفار al-ʼaẓfār "the talons (of the swooping eagle)", a name it shares with Eta Lyrae[9] (though the latter is spelled "Aladfar" by the IAU).[10] This white-hued object is visible to the naked eye as faint point of light with an apparent visual magnitude of 5.11.[2] It is located approximately 412 light years distant from the Sun based on parallax,[1] but is drifting closer with a radial velocity of −24 km/s.[2]

Mu Lyrae
Observation data
Epoch J2000      Equinox J2000
Constellation Lyra
Right ascension 118h 24m 13.78599s[1]
Declination +39° 30′ 26.0473″[1]
Apparent magnitude (V) 5.11[2]
Characteristics
Evolutionary stage subgiant[3]
Spectral type A0 IV[4]
U−B color index +0.07[5]
B−V color index +0.047±0.004[2]
Astrometry
Radial velocity (Rv)−24.0±4.2[2] km/s
Proper motion (μ) RA: −21.825±0.260[1] mas/yr
Dec.: −4.460±0.288[1] mas/yr
Parallax (π)7.9161 ± 0.1438[1] mas
Distance412 ± 7 ly
(126 ± 2 pc)
Absolute magnitude (MV)–0.53[2]
Details
Mass3.04±0.04[3] M☉
Radius4.5[6] R☉
Luminosity200+23
−10[3] L☉
Temperature9,016+167
−165[3] K
Rotational velocity (v sin i)165[3] km/s
Other designations
μ Lyr, 2 Lyrae, BD+39°3410, HD 169702, HIP 90191, HR 6903, SAO 66943[7]
Database references
SIMBADdata

This object has evolved off the main sequence,[3] becoming a subgiant with a stellar classification of A0 IV.[4] It has a fairly high rate of spin, showing a projected rotational velocity of 165 km/s.[3] This is giving the star an equatorial bulge that is an estimated 17% larger than the polar radius.[11] The star has three[3] times the mass of the Sun and about 4.5[6] times the Sun's radius. It is radiating 200[3] times the Sun's luminosity from its photosphere at an effective temperature of 9,016 K.[3]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015, S2CID 119257644.
  3. Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
  4. Van Belle, Gerard T.; von Braun, Kaspar (2009). "Directly Determined Linear Radii and Effective Temperatures of Exoplanet Host Stars". The Astrophysical Journal. 694 (2): 1085–1098. arXiv:0901.1206. Bibcode:2009ApJ...694.1085V. doi:10.1088/0004-637X/694/2/1085. S2CID 18370219.
  5. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  6. Pasinetti Fracassini, L. E.; et al. (February 2001). "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS)". Astronomy and Astrophysics (Third ed.). 367 (2): 521–524. arXiv:astro-ph/0012289. Bibcode:2001A&A...367..521P. doi:10.1051/0004-6361:20000451. S2CID 425754.
  7. "mu Lyr". SIMBAD. Centre de données astronomiques de Strasbourg.
  8. 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. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x. S2CID 14878976.
  9. Allen, Richard Hinckley (2018). Star-Names and Their Meanings. Creative Media Partners, LLC. ISBN 978-0-344-21405-9.
  10. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  11. van Belle, Gerard T. (March 2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474
  • Kaler, James B. (October 7, 2011). "Al Athfar". STARS. Retrieved 2019-09-25.
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