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

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]

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. 1 2 3 4 5 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. 1 2 3 4 5 6 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. 1 2 3 4 5 6 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. 1 2 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. 1 2 3 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. 1 2 3 4 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. 1 2 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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