HD 59686

HD 59686 is a binary star[7] system in the northern constellation of Gemini. It is visible to the naked eye as a dim point of light with an apparent visual magnitude of +5.45.[2] The distance to this system is approximately 292 light years based on parallax,[1] but it is drifting closer with a radial velocity of −34 km/s.[1]

HD 59686
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Gemini
Right ascension 07h 31m 48.40415s[1]
Declination +17° 05′ 09.76945″[1]
Apparent magnitude (V) +5.45[2]
Characteristics
Spectral type K2III[3]
B−V color index 1.126±0.006[2]
Astrometry
Radial velocity (Rv)−33.55±0.18[1] km/s
Proper motion (μ) RA: +39.712[1] mas/yr
Dec.: -76.077[1] mas/yr
Parallax (π)11.1741 ± 0.0911 mas[1]
Distance292 ± 2 ly
(89.5 ± 0.7 pc)
Absolute magnitude (MV)0.52[2]
Orbit[4]
Period (P)11,680+234
−173 d
Semi-major axis (a)13.56+0.18
−0.14
Eccentricity (e)0.729+0.004
−0.003
Argument of periastron (ω)
(secondary)		149.4±0.2°
Semi-amplitude (K1)
(primary)		4.014+0.010
−0.008 km/s
Details[5]
A
Mass1.43±0.23 M☉
Radius11.22±0.70 R☉
Luminosity57.5+14.9
−11.8 L☉
Surface gravity (log g)2.63±0.09 cgs
Temperature4,670±34 K
Metallicity [Fe/H]0.01±0.03 dex
Rotational velocity (v sin i)1.03±0.23 km/s
Age2.73±1.11 Gyr
B
Mass≥0.53 M☉
Other designations
BD+17°1596, GC 10073, HD 59686, HIP 36616, HR 2877, SAO 96985, GSC 01364-01582[6]
Database references
SIMBADdata

This is a single-lined spectroscopic binary system with an orbital period of 32.0 years and a high eccentricity of 0.73.[4] The visible component is an aging giant star with a stellar classification of K2III,[3] meaning it has ceased fusing hydrogen in its core and on its way to becoming a red giant. The stellar radius is very large: 11.2 times that of the Sun.[5] The star is around 2.7 billion years old with 1.4 times the mass of the Sun. It is radiating 58 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,670 K.[5]

The secondary component has a minimum mass 53% that of the Sun, which indicates it must be a star rather than a brown dwarf or a planet.[5]

Planetary system

In November 2003, a planet was announced orbiting the giant star. A doppler spectrometer was used to look for effects on the star caused by the gravitational tug of the orbiting planet. Using the amplitude from the radial velocity method, he calculated the planetary mass as 5.25 Jupiter masses and with period 303 days. However that mass is only a minimum because the inclination of the orbit is not known. Using the stellar mass and period, he calculated the semimajor axis as 0.911 astronomical units. He found that the shape of the stellar wobble is circular, implying that the planet has zero eccentricity.[8]

The HD 59686 A planetary system[4]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b 6.92+0.18
−0.24 MJ		 1.0860+0.0006
−0.0007		 299.36+0.26
−0.31		 0.05+0.03
−0.02		 — —

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, S2CID 119257644.
  3. Adams, Walter S.; Joy, Alfred H.; Humason, Milton L.; Brayton, Ada Margaret (1935), "The Spectroscopic Absolute Magnitudes and Parallaxes of 4179 Stars", Astrophysical Journal, 81: 187, Bibcode:1935ApJ....81..187A, doi:10.1086/143628.
  4. Ortiz, Mauricio; et al. (October 2016), "Precise radial velocities of giant stars. IX. HD 59686 Ab: a massive circumstellar planet orbiting a giant star in a 13.6 au eccentric binary system", Astronomy & Astrophysics, 595: 14, arXiv:1608.00963, Bibcode:2016A&A...595A..55O, doi:10.1051/0004-6361/201628791, S2CID 26289447, A55.
  5. Jofré, E.; et al. (2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy and Astrophysics, 574: A50, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, S2CID 53666931.
  6. "HD 59686". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-01-06.
  7. Trifonov, Trifon; et al. (April 2018), "Dynamical Analysis of the Circumprimary Planet in the Eccentric Binary System HD 59686", The Astronomical Journal, 155 (4): 14, arXiv:1803.01434, Bibcode:2018AJ....155..174T, doi:10.3847/1538-3881/aab439, S2CID 119487750, 174.
  8. Mitchell, D.; et al. (2003), "Four Substellar Companions Found Around Nearby K Giant Stars", Bulletin of the American Astronomical Society, 35: 1234, Bibcode:2003AAS...203.1703M.
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