HD 100655

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]

HD 100655 / Formosa
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]
Characteristics
Evolutionary stage giant star
Spectral type G9 III[3]
B−V color index 1.010±0.015[2]
Astrometry
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 mas[1]
Distance449 ± 3 ly
(137.7 ± 0.9 pc)
Absolute magnitude (MV)1.02[2]
Details[5]
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
Formosa, BD+21° 2331, Gaia DR2 3979226627820659072, HD 100655, HIP 56508, HR 4459, SAO 81886, 2MASS J11350375+2026295[8]
Database references
SIMBADdata
Exoplanet Archivedata
Extrasolar Planets
Encyclopaedia		data

The star HD 100655 is named Formosa. The name was selected in the NameExoWorlds campaign by Taiwan, during the 100th anniversary of the IAU. Formosa is the historical name of Taiwan used in the 17th century, meaning beautiful in Portuguese. The planet HD 100655 b is named Sazum, after the township Yuchi and it means water in the language of the Thao people.[9][10]

This is an evolved giant star with a stellar classification of G9 III.[3] It is a red clump giant,[11] 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]

Planetary system

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.[11]

The HD 100655 planetary system[7]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b / Sazum >1.7 MJ 0.76+0.02
−0.04		 157.57 ± 0.65 0.085 ± 0.054 — —

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. 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. 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. 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, S2CID 59451347, A61.
  5. 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. S2CID 54555839.
  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, S2CID 73575554, A94
  7. 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. S2CID 56129987.
  8. "HD 100655". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-02-05.
  9. "Approved names". NameExoworlds. Retrieved 2020-01-02.
  10. "International Astronomical Union | IAU". www.iau.org. Retrieved 2020-01-02.
  11. 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. S2CID 119197073.
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