6 Equulei

6 Equulei is a probable (95% chance) astrometric binary[9] star system in the northern constellation of Equuleus, located 380 light years from the Sun. It is barely visible to the naked eye as a dim, white-hued star with an apparent visual magnitude of 6.07.[2] The system is moving further away from the Earth with a heliocentric radial velocity of +6.9 km/s.[5] It forms a wide optical double with γ Equulei, at an angular separation of 336 arcseconds in 2011.[10]

6 Equulei
Observation data
Epoch J2000 (ICRS)      Equinox J2000 (ICRS)
Constellation Equuleus
Right ascension  21h 10m 31.31996s[1]
Declination 10° 02′ 56.1180″[1]
Apparent magnitude (V) 6.07[2]
Characteristics
Evolutionary stage main sequence[3]
Spectral type A2 Vs[3] (A1 Si Sr Cr)[4]
U−B color index +0.04[2]
B−V color index +0.02[2]
Astrometry
Radial velocity (Rv)+6.9[5] km/s
Proper motion (μ) RA: –2.696[1] mas/yr
Dec.: +15.802[1] mas/yr
Parallax (π)8.5862 ± 0.1086[1] mas
Distance380 ± 5 ly
(116 ± 1 pc)
Absolute magnitude (MV)+0.236[6]
Details
Mass2.59±0.14[3] M☉
Radius1.7[7] R☉
Luminosity70.6+19.4
−15.2[3] L☉
Temperature9,078+169
−165[3] K
Rotational velocity (v sin i)65[3] km/s
Age970[6] Myr
Other designations
γ Equulei D, BD+09°4735, HD 201616, HIP 104538, HR 8098, SAO 126597[8]
Database references
SIMBADdata

The visible component is an Ap star[3] with a stellar classification of A2Vs,[3] matching the evolutionary state of an A-type main sequence star while displaying "sharp" absorption lines. It is an estimated 970[6] million years old with a projected rotational velocity of 65 km/s.[3] The star has 2.6[3] times the mass of the Sun and around 1.7[7] times the Sun's radius. It is radiating 71[3] times the luminosity of the Sun from its photosphere at an effective temperature of 9,078 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. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99), Bibcode:1966CoLPL...4...99J
  3. Zorec, J.; et al. (2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy and Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691.
  4. Renson, P.; Manfroid, J. (May 2009), "Catalogue of Ap, HgMn and Am stars", Astronomy and Astrophysics, 498 (3): 961–966, Bibcode:2009A&A...498..961R, doi:10.1051/0004-6361/200810788.
  5. Wilson, Ralph Elmer (1953), General Catalogue of Stellar Radial Velocities, Washington: Carnegie Institution of Washington, Bibcode:1953GCRV..C......0W.
  6. "HD 104538", WolframAlpha, retrieved 2012-08-05
  7. Pasinetti Fracassini, L. E.; et al. (February 2001), "Catalogue of Apparent Diameters and Absolute Radii of Stars (CADARS) - Third edition - Comments and statistics", Astronomy and Astrophysics, 367: 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451.
  8. "6 Equ -- Star in double system", SIMBAD Astronomical Database, Centre de Données astronomiques de Strasbourg, retrieved 2012-07-25.
  9. Frankowski, A.; Jancart, S.; Jorissen, A. (March 2007), "Proper-motion binaries in the Hipparcos catalogue. Comparison with radial velocity data", Astronomy and Astrophysics, 464 (1): 377–392, arXiv:astro-ph/0612449, Bibcode:2007A&A...464..377F, doi:10.1051/0004-6361:20065526
  10. Mason, Brian D.; et al. (2001), "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog", The Astronomical Journal, 122 (6): 3466–3471, Bibcode:2001AJ....122.3466M, doi:10.1086/323920.
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