HD 100655

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HD 100655
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Leo
Right ascension  11h 35m 03.75298s[1]
Declination +20° 26′ 29.5637″[1]
Apparent magnitude (V) +6.45[2]
Spectral type G9 III[3]
B−V color index 1.010±0.015[2]
Radial velocity (Rv)−5.2±0.3[4] km/s
Proper motion (μ) RA: –59.695[1] mas/yr
Dec.: –1.047[1] mas/yr
Parallax (π)7.2613 ± 0.0472[1] mas
Distance449 ± 3 ly
(137.7 ± 0.9 pc)
Absolute magnitude (MV)1.02[2]
Mass2.2±0.1 M
Radius8.8±0.1 R
Luminosity40.8±0.3 L
Surface gravity (log g)2.89±0.02 cgs
Temperature4,918±8 K
Metallicity [Fe/H]0.07±0.03[6] dex
Rotational velocity (v sin i)1.6±1.0[7] km/s
Age900±200 Myr
Other designations
BD+21° 2331, HD 100655, HIP 56508, HR 4459, SAO 81886[8]
Database references
Exoplanet Archivedata
Extrasolar Planets

HD 100655 is a star in the zodiac constellation of Leo, located 449[1] light years away from the Sun. It has an apparent visual magnitude of +6.45,[2] which makes it a challenge to see with the naked eye under ideal viewing conditions. The star is moving closer to the Earth with a heliocentric radial velocity of −5 km/s.[4] It has one confirmed planet.[7]

This is an evolved giant star with a stellar classification of G9 III.[3] It is a red clump giant,[9] which means it is currently on the horizontal branch and is generating energy through helium fusion at its core. This star is around 900 million years old with 2.2 times the mass of the Sun and has expanded to 8.8 times the Sun's radius. It is radiating 4,918 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 4,918 K.[5]

The planetary companion, announced in 2011, was discovered by a Korean–Japanese planet search program by the radial velocity method. The motions of the host star displayed Keplerian variation, indicating a perturbing body in orbit. The best fit model suggests a body having a minimum mass of 1.7 MJ and showing a 158-day orbital period with a semimajor axis of 0.76 astronomical units (114 Gm) and a low eccentricity of 0.085.[7] This is one of the two least massive planets known around clump giants, as of 2012.[9]

The HD 100655 planetary system[7]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b >1.7 MJ 0.76+0.02
157.57 ± 0.65 0.085 ± 0.054


  1. ^ a b c d e f 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. ^ a b c d 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.
  3. ^ a b Halliday, Ian (September 1955), "Luminosity Function and Space Motions of G8-K1 Stars Derived from Spectroscopic Parallaxes", Astrophysical Journal, 122: 222, Bibcode:1955ApJ...122..222H, doi:10.1086/146080
  4. ^ a b de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  5. ^ a b Bonfanti, A.; et al. (2015). "Revising the ages of planet-hosting stars". Astronomy and Astrophysics. 575. A18. arXiv:1411.4302. Bibcode:2015A&A...575A..18B. doi:10.1051/0004-6361/201424951.
  6. ^ Sousa, S. G.; et al. (April 2015), "Homogeneous spectroscopic parameters for bright planet host stars from the northern hemisphere. The impact on stellar and planetary mass", Astronomy & Astrophysics, 576: 8, arXiv:1503.02443, Bibcode:2015A&A...576A..94S, doi:10.1051/0004-6361/201425227, A94
  7. ^ a b c d Omiya, Masashi; et al. (2012). "A Planetary Companion to the Intermediate-Mass Giant HD 100655". Publications of the Astronomical Society of Japan. 64 (2). 34. arXiv:1111.3746. Bibcode:2012PASJ...64...34O. doi:10.1093/pasj/64.2.34.
  8. ^ "HD 100655". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-02-05.
  9. ^ a b Sato, Bun'ei; et al. (2012). "Substellar Companions to Seven Evolved Intermediate-Mass Stars". Publications of the Astronomical Society of Japan. 64 (6). 135. arXiv:1207.3141. Bibcode:2012PASJ...64..135S. doi:10.1093/pasj/64.6.135.