Gamma Lyrae

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Gamma Lyrae
Diagram showing star positions and boundaries of the Lyra constellation and its surroundings
Cercle rouge 100%.svg

Location of γ Lyrae
Observation data
Epoch J2000      Equinox J2000
Constellation Lyra
Right ascension 18h 58m 56.62241s[1]
Declination +32° 41′ 22.4003″[1]
Apparent magnitude (V) 3.261[2]
Characteristics
Spectral type B9 III[3]
U−B color index –0.125[2]
B−V color index –0.047[2]
Astrometry
Radial velocity (Rv) –21.1[4] km/s
Proper motion (μ) RA: –3.09[1] mas/yr
Dec.: +1.11[1] mas/yr
Parallax (π) 5.26 ± 0.27[1] mas
Distance 620 ± 30 ly
(190 ± 10 pc)
Details
Radius 15[5] R
Surface gravity (log g) 3.5[6] cgs
Temperature 10,080[6] K
Metallicity [Fe/H] +0.11[6] dex
Rotational velocity (v sin i) 71–72[7] km/s
Other designations
Sulafat, Gamma Lyrae, γ Lyr, γ Lyrae, NSV 11624, 14 Lyr, HR 7178, HD 176437, SAO 67663, FK5 713.[8]

Gamma Lyrae (γ Lyr, γ Lyrae) is the second brightest star in the northern constellation of Lyra. It has the traditional names Sulafat (Sulaphat), from the Arabic السلحفاة al-sulḥafāt "turtle", and Jugum,[9] from the Latin iugum "yoke". The connection with turtles is that fine harps were traditionally made of tortoiseshell. The apparent visual magnitude of Sulafat is 3.3,[2] which is readily visible to the naked eye. Parallax measurements yield an estimated distance of 620 light-years (190 parsecs) from the Earth.

This is a giant star with a stellar classification of B9 III,[3] indicating it has exhausted the supply of hydrogen at its core and evolved away from the main sequence. The effective temperature of the outer envelope of this star is 10,080 K,[6] giving it the blue-white hue typical of a B-type star.[10] The interferometry-measured angular diameter of this star is 0.74 ± 0.10 mas,[11] which, at its estimated distance, equates to a physical radius of roughly 15 times the radius of the Sun.[5]

In 1909, Canadian astronomer Samuel A. Mitchell identified this star as a spectroscopic binary, although he was unable to split the absorption lines of the components. He found that a period of 25.6 days matched his measurements.[12] It was reported as a spectroscopic binary as recently as 2001,[13] but is now believed to be a single star[14][15] with a high rate of rotation for stars of this type.[13]

References[edit]

  1. ^ a b c d e 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. ^ a b c d Oja, T., "UBV photometry of stars whose positions are accurately known. III", Astronomy and Astrophysics Supplement Series 65 (2): 405–4 
  3. ^ a b Cowley, A. et al. (April 1969), "A study of the bright A stars. I. A catalogue of spectral classifications", Astronomical Journal 74: 375–406, Bibcode:1969AJ.....74..375C, doi:10.1086/110819 
  4. ^ Evans, D. S. (June 20–24, 1966), "The Revision of the General Catalogue of Radial Velocities", in Batten, Alan Henry; John Frederick, Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30, University of Toronto: International Astronomical Union, Bibcode:1967IAUS...30...57E 
  5. ^ a b Lang, Kenneth R. (2006), Astrophysical formulae, Astronomy and astrophysics library 1 (3 ed.), Birkhäuser, ISBN 3-540-29692-1 . The radius (R*) is given by:
    \begin{align} 2\cdot R_*
 & = \frac{(10^{-3}\cdot 190\cdot 0.74)\ \text{AU}}{0.0046491\ \text{AU}/R_{\bigodot}} \\
 & \approx 30\cdot R_{\bigodot}
\end{align}
  6. ^ a b c d Balachandran, S. et al. (April 1986), "The chemical composition of algol systems. III - Beta Lyrae-nucleosynthesis revealed", Monthly Notices of the Royal Astronomical Society 219: 479–494, Bibcode:1986MNRAS.219..479B 
  7. ^ Royer, F. et al. (October 2002), "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i", Astronomy and Astrophysics 393: 897–911, arXiv:astro-ph/0205255, Bibcode:2002A&A...393..897R, doi:10.1051/0004-6361:20020943 
  8. ^ "SULAFAT -- Star in double system", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-12 
  9. ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 287 
  10. ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16 
  11. ^ Richichi; Percheron, I.; Khristoforova, M. (February 2005), "CHARM2: An updated Catalog of High Angular Resolution Measurements", Astronomy and Astrophysics 431: 773–777, Bibcode:2005A&A...431..773R, doi:10.1051/0004-6361:20042039 
  12. ^ Mitchell, S. A. (October 1909), "Seven spectroscopic binaries", Astrophysical Journal 30: 239–242, Bibcode:1909ApJ....30..239M, doi:10.1086/141699 
  13. ^ a b Adelman, Saul J. et al. (June 2001), "Elemental abundance analyses with DAO spectrograms. XXV. The superficially normal B and A stars alpha Draconis, tau Herculis, gamma Lyrae, and HR 7926", Astronomy and Astrophysics 371: 1078–1083, Bibcode:2001A&A...371.1078A, doi:10.1051/0004-6361:20010408 
  14. ^ Roberts, Lewis C., Jr.; Turner, Nils H.; ten Brummelaar, Theo A. (February 2007), "Adaptive Optics Photometry and Astrometry of Binary Stars. II. A Multiplicity Survey of B Stars", The Astronomical Journal 133 (2): 545–552, Bibcode:2007AJ....133..545R, doi:10.1086/510335 
  15. ^ 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 

External links[edit]