HD 202206

HD 202206 is a binary star system in the southern constellation of Capricornus. With an apparent visual magnitude of +8.1,[2] it is too faint to be visible to the naked eye. It is located at a distance of 150 light years from the Sun based on parallax, and is drifting further away with a radial velocity of +14.7 km/s.[5]

HD 202206
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Capricornus
Right ascension 21h 14m 57.76850s[1]
Declination −20° 47′ 21.1624″[1]
Apparent magnitude (V) +8.07±0.01[2]
Characteristics
Spectral type G6V[3] + M8V[2]
B−V color index 0.714±0.012[4]
Astrometry
Radial velocity (Rv)+14.68±0.23[5] km/s
Proper motion (μ) RA: −39.079[1] mas/yr
Dec.: −119.999[1] mas/yr
Parallax (π)21.7264 ± 0.0651 mas[1]
Distance150.1 ± 0.4 ly
(46.0 ± 0.1 pc)
Absolute magnitude (MV)+4.80[4]
Orbit[2]
Period (P)256.33 days
Semi-major axis (a)1.40±0.10 mas
Eccentricity (e)0.432±0.001
Inclination (i)10.9±0.8°
Longitude of the node (Ω)121±4°
Periastron epoch (T)2,452,176.14±0.12 JD
Argument of periastron (ω)
(secondary)		161.9±0.2°
Semi-amplitude (K1)
(primary)		0.567±0.001 km/s
Details
A
Mass1.07±0.08[2] M☉
Radius1.05+0.02
−0.03[1] R☉
Luminosity1.084+0.004
−0.005[1] L☉
Surface gravity (log g)4.5±0.1[2] cgs
Temperature5,735+76
−74[1] K
Metallicity [Fe/H]0.29±0.01[4] dex
Rotational velocity (v sin i)2.3±0.5[2] km/s
Age2.9±1.0[2] Gyr
B
Mass0.089+0.007
−0.006[2] M☉
Other designations
BD−21° 5972, HD 202206, HIP 104903, SAO 190163[6]
Database references
SIMBADdata

The primary component is a G-type main-sequence star with a stellar classification of G6V,[3] indicating it is generating energy through core hydrogen fusion. It is an estimated three[2] billion years old and is spinning with a projected rotational velocity of 2.3 km/s.[2] It is a metal-rich star – what astronomers term the abundance of elements of higher atomic number than helium – which may explain the star's unusually high luminosity for its class.[7] The star has a slightly greater mass and radius compared to the Sun.[2]

Companions

In 2000, analysis of radial velocity measurements of the star revealed the existence of a brown dwarf companion[8] with at least 17 times the mass of Jupiter around the star in an eccentric orbit with a period of around 256 days.[7] Even after the brown dwarf was accounted for, the star still showed a drift in the radial velocity measurements, suggesting another companion in a longer-period orbit. In 2004 after further observations, the parameters of a proposed companion was announced.[9]

Further observation of this system revised this picture in 2017, showing that the system instead consisted of a pair of co-orbiting stars being viewed nearly face-on, with the pair being orbited in turn by a Super-Jupiter designated HD 202206 c. The secondary stellar companion, now designated component B rather than 'b', is a red dwarf star with 8.9% of the mass of the Sun.[2]

The HD 202206 planetary system[2]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
c 17.9+2.9
−1.8 MJ		 2.41 1,260±11 0.22±0.03 7.7±1.1° —

See also

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. Benedict, G. Fritz; Harrison, Thomas E. (June 2017). "HD 202206: A Circumbinary Brown Dwarf System". The Astronomical Journal. 153 (6): 12. arXiv:1705.00659. Bibcode:2017AJ....153..258B. doi:10.3847/1538-3881/aa6d59. S2CID 119105717. 258.
  3. Houk, N.; Smith-Moore, M. (1988). Michigan Catalogue of Two-dimensional Spectral Types for the HD Stars. Vol. 4. Bibcode:1988mcts.book.....H.
  4. 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.
  5. Valenti, Jeff A.; Fischer, Debra A. (2005). "Spectroscopic Properties of Cool Stars (SPOCS). I. 1040 F, G, and K Dwarfs from Keck, Lick, and AAT Planet Search Programs". The Astrophysical Journal Supplement Series. 159 (1): 141–166. Bibcode:2005ApJS..159..141V. doi:10.1086/430500.
  6. "HD 202206". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-07-05.
  7. Udry, S.; et al. (2002). "The CORALIE survey for southern extra-solar planets VIII. The very low-mass companions of HD 141937, HD 162020, HD 168443, HD 202206: Brown dwarfs or "superplanets"?". Astronomy and Astrophysics. 390 (1): 267–279. arXiv:astro-ph/0202458. Bibcode:2002A&A...390..267U. doi:10.1051/0004-6361:20020685. S2CID 9389274.
  8. "Exoplanets Galore!" (Press release). Garching, Germany: European Southern Observatory. April 15, 2000. Retrieved December 30, 2012.
  9. Correia, A.; et al. (2005). "The CORALIE survey for southern extra-solar planets. XIII. A pair of planets around HD202206 or a circumbinary planet?". Astronomy and Astrophysics. 440 (2): 751–758. arXiv:astro-ph/0411512. Bibcode:2005A&A...440..751C. doi:10.1051/0004-6361:20042376. S2CID 16175663.
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