HD 20782

HD 20782 is a 7th magnitude G-type main sequence star 117.5 light-years away from Earth, in the constellation of Fornax. HD 20782 is a part of a wide binary system in which the other star is designated HD 20781, and both stars host planetary systems. Indeed, this is the first known case of a binary star system where there are planetary systems around both the primary and the secondary stars in the system. The companion star HD 20781 has a very large angular separation of 252 arcsec, corresponding to 9080 AU at the distance of HD 20782.[3] It is estimated to be 7.1 (± 4) billion years old, with a mass close to that of our Sun. (Note that, despite the numbering, HD 20782 is the primary star of the system, and HD 20781 the secondary star.)

HD 20782
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Fornax
Right ascension 03h 20m 03.5777s[1]
Declination −28° 51′ 14.6604″[1]
Apparent magnitude (V) 7.38
Characteristics
Spectral type G3V
Astrometry
Proper motion (μ) RA: 349.057±0.036[1] mas/yr
Dec.: −65.299±0.041[1] mas/yr
Parallax (π)27.7593 ± 0.0317[1] mas
Distance117.5 ± 0.1 ly
(36.02 ± 0.04 pc)
Absolute magnitude (MV)4.60
Other designations
CD−29°1231, HIP 15527, SAO 168469, WDS J03201-2851A, 2MASS J03200355-2851145[2]
Database references
SIMBADdata
Exoplanet Archivedata

An extremely eccentric extrasolar planet was announced around HD 20782 in 2006.[4][5] In 2009 this planet's orbit was narrowed down, and it was found to have the highest eccentricity of all known exoplanets; this distinction has stood since 2012.

And in 2011 two also-eccentric (but less so) Neptune-mass planets were announced around the HD 20781.[6][7]

Planetary system
The HD 20782 planetary system[8]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b >1.43 ± 0.03 MJ 1.397 ± 0.009 597.065 ± 0.043 0.956 ± 0.004 >1.22° —

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. "HD 20782". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2020-08-15.
  3. http://www.aanda.org/index.php?option=com_article&access=bibcode&Itemid=129&bibcode=2007A%2526A...462..345DFUL
  4. Jones, Hugh R. A.; et al. (2006). "High-eccentricity planets from the Anglo-Australian Planet Search". Monthly Notices of the Royal Astronomical Society. 369 (1): 249–256. arXiv:astro-ph/0603335. Bibcode:2006MNRAS.369..249J. doi:10.1111/j.1365-2966.2006.10298.x.
  5. Schneider, J. "Notes for HD 20782". The Extrasolar Planets Encyclopaedia.
  6. Schneider, J. "Notes for star HD 20781". The Extrasolar Planets Encyclopaedia. Retrieved 2011-09-12.
  7. Mayor, M. Marmier,M. Lovis,C. Udry,S. Ségransan,D. Pepe,F. Benz,W. Bertaux,J.-L. Bouchy,F. Dumusque, G. Curto,Lo Mordasini,C. Queloz,D. Santos,N. C.; et al. (2011). "The HARPS search for southern extra-solar planets XXXIV. Occurrence, mass distribution and orbital properties of super-Earths and Neptune-mass planets". arXiv:1109.2497 [astro-ph].CS1 maint: multiple names: authors list (link)
  8. Kane, Stephen R.; et al. (2016). "Evidence for Reflected Light from the Most Eccentric Exoplanet Known". The Astrophysical Journal. 821 (1). 65. arXiv:1511.08679. Bibcode:2016ApJ...821...65K. doi:10.3847/0004-637X/821/1/65.

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