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HD 2638 is a ternary star system[9] system in the equatorial constellation of Cetus. The pair have an angular separation of 0.53″ along a position angle of 166.7°, as of 2015.[9] This is system too faint to be visible to the naked eye, having a combined apparent visual magnitude of 9.44;[2] a small telescope is required. The distance to this system is 179.5 light years based on parallax, and it is drifting further away with a radial velocity of +9.6 km/s.[1] The magnitude 7.76 star HD 2567 forms a common proper motion companion to this pair[9] at projected separation 839″.[5]

The HD 2638 members A and BC have a projected separation of about 25.5±1.9 AU and thus an orbital period of around 130 years.[4] They have a combined stellar classification of K1V.[3] The primary component is a G-type main-sequence star with a class of G8V.[4] It is smaller and less massive than the Sun, and has a lower luminosity.[6] The secondary is a binary consisting of two red dwarf stars on close orbit with combined mass less than half the mass of the primary, and a composite spectral class of M1V.[4]

Planetary system

In 2005, the discovery of an extrasolar planet HD 2638 b orbiting the primary was announced by the Geneva Extrasolar Planet Search Team. The planet has a mass 0.48 times that of Jupiter and 152.6 times that of Earth.[10] The planet existence was placed under doubt in 2015 due to discovered additional stellar companions.[5]

[10]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination
(°)		 Radius
b >0.48 MJ 0.044 3.4442±0.0002 0.0407 — —

See also

References

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.
  • 1 2 Houk, N.; Swift, C. (1999). “Michigan catalogue of two-dimensional spectral types for the HD Stars”. Michigan Spectral Survey. 5. Bibcode:1999MSS…C05….0H.
  • 1 2 3 4 5 6 7 8 9 Wittrock, Justin M.; et al. (November 2016). “Stellar Companions to the Exoplanet Host Stars HD 2638 and HD 164509”. The Astronomical Journal. 152 (5): 7. arXiv:1609.00016. Bibcode:2016AJ….152..149W. doi:10.3847/0004-6256/152/5/149. S2CID 45942803. 149.
  • 1 2 3 Roberts Jr, Lewis C.; Tokovinin, Andrei; Mason, Brian D.; Riddle, Reed L.; Hartkopf, William I.; Law, Nicholas M.; Baranec, Christoph (2015), “Know the Star, Know the Planet. III. Discovery of Late-Type Companions to Two Exoplanet Host Stars”, The Astronomical Journal, 149 (4): 118, arXiv:1503.01211, Bibcode:2015AJ….149..118R, doi:10.1088/0004-6256/149/4/118, S2CID 30908636
  • 1 2 Bonfanti, A.; et al. (2015). “Revising the ages of planet-hosting stars”. Astronomy and Astrophysics. 575. A18. arXiv:1411.4302. Bibcode:2015A&A…575A..18B. doi:10.1051/0004-6361/201424951. S2CID 54555839.
  • ↑ Tsantaki, M.; Sousa, S. G.; Adibekyan, V. Zh.; Santos, N. C.; Mortier, A.; Israelian, G. (2013). “Deriving precise parameters for cool solar-type stars. Optimizing the iron line list”. Astronomy and Astrophysics. 555. arXiv:1304.6639. Bibcode:2013A&A…555A.150T. doi:10.1051/0004-6361/201321103.
  • ↑ “HD 2638”. SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2011-12-20.
  • 1 2 3 Riddle, Reed L.; et al. (January 2015). “A Survey of the High Order Multiplicity of Nearby Solar-type Binary Stars with Robo-AO”. The Astrophysical Journal. 799 (1): 21. arXiv:1411.0682. Bibcode:2015ApJ…799….4R. doi:10.1088/0004-637X/799/1/4. S2CID 5642378. 4.
  • 1 2 Moutou, C.; et al. (2015). “The HARPS search for southern extra-solar planets IV. Three close-in planets around HD 2638, HD 27894 and HD 63454”. Astronomy and Astrophysics. 439 (1): 367–373. arXiv:1411.7048. Bibcode:2005A&A…439..367M. doi:10.1051/0004-6361:20052826.