HD 219828

HD 219828 is an 8th magnitude star approximately 239 light years away in the constellation of Pegasus. It is a yellow subgiant, meaning that hydrogen fusion has ceased in its core.

HD 219828
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Pegasus
Right ascension  23h 18m 46.7342s[1]
Declination 18° 38′ 44.6152″[1]
Apparent magnitude (V) 8.04
Characteristics
Spectral type G0IV
Astrometry
Proper motion (μ) RA: −5.075±0.139[1] mas/yr
Dec.: 6.037±0.067[1] mas/yr
Parallax (π)13.6489 ± 0.0660[1] mas
Distance239 ± 1 ly
(73.3 ± 0.4 pc)
Details
Other designations
BD17 4896, HIP 115100, SAO 108536, GSC 01716-01182[2]
Database references
SIMBADdata

Planetary system

In 2007, a Neptune-mass planet was found orbiting the star by Melo. According to the author, assuming an Earth-like rocky composition,[3] the planet could yield a radius 2.2 times that of Earth. This could be furtherly proved if transit were observed, though, as authors state, it is a difficult task.[4] At this point, it was suggested that a best fit orbital solution hints the presence of an additional planetary companion (so far unconfirmed) with 70% of Jupiter's mass, likely orbital separation of 0.68 Astronomical units and eccentric orbit (e=0.3). However, in 2016, further analysis or radial velocity data confirmed the presence of an outer planet larger and more eccentric than was originally believed. With high eccentricity and a high mass ratio between the two planets, the system is quite unique.[5] The planet c is also a potential target for GAIA astrometry or atmospheric characterization using direct imaging or high-resolution spectroscopy.

The HD 219828 planetary system
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b >21.0 ± 1.4 M⊕ 0.045 3.834887 ± 0.000096 0.059 ± 0.036 — —
c >15.1 ± 0.85 MJ 5.96 4791 ± 75 0.8115 ± 0.0032 — —
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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 219828". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2018-12-19.
  3. Valencia; Oconnell, R; Sasselov, D (2006). "Internal structure of massive terrestrial planets". Icarus (Submitted manuscript). 181 (2): 545–554. arXiv:astro-ph/0511150. Bibcode:2006Icar..181..545V. doi:10.1016/j.icarus.2005.11.021.
  4. Melo, C.; et al. (2007). "A new Neptune-mass planet orbiting HD 219828". Astronomy and Astrophysics. 467 (2): 721–727. arXiv:astro-ph/0702459. Bibcode:2007A&A...467..721M. doi:10.1051/0004-6361:20066845.
  5. N. C. Santos; A. Santerne; J. P. Faria; J. Rey; A. C. M. Correia; J. Laskar; S. Udry; V. Adibekyan; F. Bouchy; E. Delgado-Mena; C. Melo; X. Dumusque; G. Hébrard; C. Lovis; M. Mayor; M. Montalto; A. Mortier; F. Pepe; P. Figueira; J. Sahlmann; D. Ségransan; S. G. Sousa (2016). "An extreme planetary system around HD219828. One long-period super Jupiter to a hot-neptune host star". Astronomy & Astrophysics. 592: A13. arXiv:1605.06942. Bibcode:2016A&A...592A..13S. doi:10.1051/0004-6361/201628374.


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