Alpha Octantis

Alpha Octantis is a binary star[11] system in the constellation of Octans. The name is Latinized from α Octantis. Despite being labeled the "alpha" star by Johann Bayer in his star atlas Uranometria, it is not the brightest star in the constellation – that title belongs to Nu Octantis. It is visible to the naked eye as a faint, yellow-white hued point of light with an overall apparent visual magnitude of approximately 5.13.[2] The system is located approximately 148 light years away from the Sun based on parallax,

Alpha Octantis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Octans
Right ascension  21h 04m 43.06347s[1]
Declination −77° 01′ 25.5735″[1]
Apparent magnitude (V) 5.13[2]
Characteristics
Spectral type F4III + F5III
(spectroscopic binary)[3]
U−B color index +0.13[4]
B−V color index +0.490±0.008[2]
Variable type EB[5]
Astrometry
Radial velocity (Rv)85.9±1.5[2] km/s
Proper motion (μ) RA: +22.5215[1] mas/yr
Dec.: −369.325[1] mas/yr
Parallax (π)22.5215 ± 0.0955[1] mas
Distance144.8 ± 0.6 ly
(44.4 ± 0.2 pc)
Absolute magnitude (MV)1.93±0.02[6]
Orbit[3]
Period (P)9.073 d
Eccentricity (e)0.39
Periastron epoch (T)2435302.404
Argument of periastron (ω)
(secondary)		276°
Semi-amplitude (K1)
(primary)		47 km/s
Semi-amplitude (K2)
(secondary)		47 km/s
Details
Mass1.42[7] M☉
Radius3.69[8] R☉
Temperature6,270[6] K
Metallicity [Fe/H]0.07[6] dex
Rotational velocity (v sin i)85[9] km/s
Age1.5±0.1[6] Gyr
Other designations
α Oct, CD−77°1053, CPD−77°1474, FK5 787, GC 29343, HD 199532, HIP 104043, HR 8021, SAO 257879, PPM 374864, LTT 8327, NLTT 50332[10]
Database references
SIMBADdata

This is a double-lined spectroscopic binary star which consists of two similar giant stars, each with spectral type F, orbiting each other with a period of just over 9 days and an eccentricity of 0.39.[3] The pair form a Beta Lyrae-type eclipsing binary system, dropping by magnitude 0.04 during the primary eclipse.[5] This system is a bright X-ray source with a luminosity of 22.78×1029 ergs s−1.[12] The system displays an infrared excess suggesting the presence of two debris disks; the first has a temperature of 450 K and is orbiting at a distance of 1.40 AU from its host star, while the second is a much cooler 40 K and orbits 187.8 AU from the system.[8]

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.
  3. The double-lined binary alpha Octantis, William Buscombe and Pamela M. Morris, The Observatory 80 (February 1960), pp. 28–29, Bibcode: 1960Obs....80...28B.
  4. HR 8021, database entry, The Bright Star Catalogue, 5th Revised Ed. (Preliminary Version), D. Hoffleit and W. H. Warren, Jr., CDS ID V/50. Accessed on line September 4, 2008.
  5. Samus', N. N; et al. (2017). "General catalogue of variable stars". Astronomy Reports. 5.1. 61 (1): 80. Bibcode:2017ARep...61...80S. doi:10.1134/S1063772917010085.
  6. Nordström, B.; et al. (2004). "The Geneva-Copenhagen survey of the Solar neighbourhood. Ages, metallicities, and kinematic properties of ˜14 000 F and G dwarfs". Astronomy and Astrophysics. 418: 989–1019. arXiv:astro-ph/0405198. Bibcode:2004A&A...418..989N. doi:10.1051/0004-6361:20035959.
  7. Tokovinin, A.; et al. (May 2006), "Tertiary companions to close spectroscopic binaries", Astronomy and Astrophysics, 450 (2): 681–693, arXiv:astro-ph/0601518, Bibcode:2006A&A...450..681T, doi:10.1051/0004-6361:20054427
  8. Cotten, Tara H.; Song, Inseok (July 2016), "A Comprehensive Census of Nearby Infrared Excess Stars", The Astrophysical Journal Supplement Series, 225 (1): 24, arXiv:1606.01134, Bibcode:2016ApJS..225...15C, doi:10.3847/0067-0049/225/1/15, 15.
  9. 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.
  10. "* alf Oct". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved September 4, 2008.
  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. arXiv:0806.2878. Bibcode:2008MNRAS.389..869E. doi:10.1111/j.1365-2966.2008.13596.x.
  12. Makarov, Valeri V. (October 2003), "The 100 Brightest X-Ray Stars within 50 Parsecs of the Sun", The Astronomical Journal, 126 (4): 1996–2008, Bibcode:2003AJ....126.1996M, doi:10.1086/378164.
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