HD 217786

HD 217786 is a binary star[4] system in the equatorial constellation of Pisces. With an apparent visual magnitude of 7.78,[2] it requires binoculars or a small telescope to view. The system is located at a distance of 181 light-years from the Sun based on parallax, and is drifting further away with a radial velocity of +10 km/s.[2] Kinematically, the star system belongs to the thin disk population of the Milky Way.[7]

HD 217786
Observation data
Epoch J2000      Equinox J2000
Constellation Pisces
Right ascension 23h 03m 08.20704s[1]
Declination −00° 25′ 46.6777″[1]
Apparent magnitude (V) 7.78[2]
Characteristics
Spectral type F8V[3]
B−V color index 0.578±0.004[2]
Astrometry
Radial velocity (Rv)+10.00±0.02[2] km/s
Proper motion (μ) RA: −89.933[1] mas/yr
Dec.: −168.781[1] mas/yr
Parallax (π)17.9946 ± 0.0793 mas[1]
Distance181.3 ± 0.8 ly
(55.6 ± 0.2 pc)
Absolute magnitude (MV)4.09[2] + 11.02±0.13[4]
Details[5]
A
Mass1.02 M☉
Radius1.32±0.06 R☉
Luminosity1.93±0.04[6] L☉
Surface gravity (log g)4.13±0.02 cgs
Temperature5,882±8[7] K
Metallicity−0.19±0.01
Rotational velocity (v sin i)1.18±0.05 km/s
Age9.40±0.22 Gyr
HD 217786 B
Mass0.1622+0.0071
−0.0068[4] M☉
Other designations
BD−01°4382, Gaia DR2 2650902026099857920, HD 217786, HIP 113834, TYC 5242-591-1, GSC 05242-00591, 2MASS J23030822-0025465[8]
Database references
SIMBADdata

The primary is an F-type main-sequence star with a stellar classification of F8V. It is much older than Sun with an estimated age of 9.4 billion years and is spinning slowly with a projected rotational velocity of 1.2 km/s. The star has a lower proportion of heavy elements than the Sun, having 65% of solar abundance.[7] It has about the same mass as the Sun but a 32% larger radius.[5] The star is radiating nearly double[6] the luminosity of the Sun from its photosphere at an effective temperature of 5,882 K.[7]

A low-mass stellar companion at a projected separation of 155 AU was discovered in 2016.[4] The proper motion of this co-moving object suggests it is gravitationally-bound to the primary, and their orbit is being viewed edge-on. If the orbit is assumed to be circular, then the orbital period for the pair is ~6.2 Myr.[4] No other companion stars have been detected at separations from 2.74 to 76.80 AUs.[6]

The star system exhibits strong stellar flare activity in the ultraviolet.[9]

Planetary system

In 2010 one superjovian planet or brown dwarf on an eccentric orbit was discovered utilising the radial velocity method.[10] Designated component Ab, the high eccentricity of this object may have been caused by interaction with the secondary star.[4] In 2022, the inclination and true mass of HD 217786 Ab were measured via astrometry, and a second planet was discovered orbiting closer to the star.[11]

The HD 217786 A planetary system[11]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
c ≥0.023±0.002 MJ 0.038±0.002 2.5+0.00010
−0.00005		 — — —
b 13.852+1.267
−1.311 MJ		 2.446+0.109
−0.119		 1,301.4+1.2
−0.5		 0.311+0.002
−0.003		 69.767+0.601
−0.386°		 —

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. Houk, N.; Swift, C. (1999), "Michigan catalogue of two-dimensional spectral types for the HD Stars", Michigan Spectral Survey, 5, Bibcode:1999MSS...C05....0H
  4. Ginski, C.; et al. (2016), "A lucky imaging multiplicity study of exoplanet host stars – II", Monthly Notices of the Royal Astronomical Society, 457 (2): 2173–2191, arXiv:1601.01524, Bibcode:2016MNRAS.457.2173G, doi:10.1093/mnras/stw049, S2CID 53626523
  5. Quarles, Billy; Li, Gongjie; Kostov, Veselin; Haghighipour, Nader (2020), "Orbital Stability of Circumstellar Planets in Binary Systems", The Astronomical Journal, 159 (3): 80, arXiv:1912.11019, Bibcode:2020AJ....159...80Q, doi:10.3847/1538-3881/ab64fa, S2CID 209444271
  6. Wittrock, Justin M.; Kane, Stephen R.; Horch, Elliott P.; Howell, Steve B.; Ciardi, David R.; Everett, Mark E. (2017), "Exclusion of Stellar Companions to Exoplanet Host Stars", The Astronomical Journal, 154 (5): 184, arXiv:1709.05315, Bibcode:2017AJ....154..184W, doi:10.3847/1538-3881/aa8d69, S2CID 55789971
  7. Maldonado, J.; Villaver, E. (2017), "Searching for chemical signatures of brown dwarf formation", Astronomy & Astrophysics, 602: A38, arXiv:1702.02904, Bibcode:2017A&A...602A..38M, doi:10.1051/0004-6361/201630120, S2CID 56225222
  8. "HD 217786". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 29 September 2020.
  9. Shkolnik, Evgenya L. (2013), "An Ultraviolet Investigation of Activity on Exoplanet Host Stars", The Astrophysical Journal, 766 (1): 9, arXiv:1301.6192, Bibcode:2013ApJ...766....9S, doi:10.1088/0004-637X/766/1/9, S2CID 118415788
  10. Moutou, Claire; Mayor, Michel; Lo Curto, Gaspare; Ségransan, Damien; Udry, Stéphane; Bouchy, François; Benz, Willy; Lovis, Christophe; Naef, Dominique; Pepe, Francesco; Queloz, Didier; Santos, Nuno C.; Sousa, Sérgio Gonçalves (2010), The HARPS search for southern extra-solar planets: XXVI: Seven new planetary systems, arXiv:1012.3830, doi:10.1051/0004-6361/201015371, S2CID 118696125
  11. Feng, Fabo; Butler, R. Paul; et al. (August 2022). "3D Selection of 167 Substellar Companions to Nearby Stars". The Astrophysical Journal Supplement Series. 262 (21): 21. arXiv:2208.12720. Bibcode:2022ApJS..262...21F. doi:10.3847/1538-4365/ac7e57. S2CID 251864022.
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