Omega Serpentis

Omega Serpentis (ω Ser, ω Serpentis) is a solitary[6] star within the Serpens Caput part of the equatorial constellation of Serpens. It is visible to the naked eye with an apparent visual magnitude of +5.22.[2] Based upon an annual parallax shift of 11.93 mas as seen from Earth, it is located about 273 light years from the Sun. At that distance, its visual magnitude is diminished by an extinction factor of 0.19 due to interstellar dust.[4] It is a member of the Ursa Major Stream, lying among the outer parts, or corona, of this moving group of stars that roughly follow a common heading through space.[7]

Omega Serpentis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Serpens
Right ascension  15h 50m 17.54635s[1]
Declination +02° 11′ 47.4362″[1]
Apparent magnitude (V) +5.22[2]
Characteristics
Spectral type G8 III[3]
U−B color index +0.805[2]
B−V color index +1.02[2]
Astrometry
Radial velocity (Rv)−3.11±0.08[4] km/s
Proper motion (μ) RA: +29.15[1] mas/yr
Dec.: −47.31[1] mas/yr
Parallax (π)11.93 ± 0.28[1] mas
Distance273 ± 6 ly
(84 ± 2 pc)
Absolute magnitude (MV)+0.49[3]
Details[4]
Mass1.20±0.24 M☉
Radius10.48±0.52 R☉
Luminosity69 L☉
Surface gravity (log g)2.88±0.03 cgs
Temperature4,797±16 K
Metallicity [Fe/H]−0.26±0.02 dex
Rotational velocity (v sin i)0.99±0.98 km/s
Age3.94±2.16 Gyr
Other designations
ω Ser, 34 Ser, BD+02° 3007, HD 141680, HIP 77578, HR 5888, SAO 121215.[5]
Database references
SIMBADdata

With an estimated age of around four billion years,[4] Omega Serpentis is an evolved G-type giant star with a stellar classification of G8 III.[3] It is a red clump giant, which means that it is generating energy at its core through the nuclear fusion of helium.[8] The star has an estimated 120% of the Sun's mass but has expanded to 10.48 times the radius of the Sun. It is radiating 69 times the solar luminosity from its photosphere at an effective temperature of 4,797 K.[4]

Planetary system

Observations made between 2001–2003 by the Okayama Planet Search Program showed that Omega Serpentis is undergoing periodic radial velocity variations with a preliminary period estimate of 312.3 days.[9] Following this announcement in 2005, further observations were performed that were best explained by a planet following a Keplerian orbit. This companion has an estimated orbital period of 277 days, a semimajor axis of 1.1 AU, and an eccentricity of 0.1.[3]

Since the inclination of the orbit is unknown, only a lower bound on the mass of the planet can be determined. The object has at least 170% times the mass of Jupiter. However, these values for the semimajor axis and planetary mass are based on an adopted stellar mass of 2.17 times the mass of the Sun.[3] More recent results by Jofré et al. (2015) give a lower stellar mass estimate of 1.20 solar masses.[4]

The Omega Serpentis planetary system[3]
Companion
(in order from star)		 Mass Semimajor axis
(AU)		 Orbital period
(days)		 Eccentricity Inclination Radius
b ≥ 1.7 MJ 1.1 277.02+0.52
−0.51		 0.106+0.079
−0.069		 — —
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References
  1. van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  2. Mermilliod, J.-C. (1986), "Compilation of Eggen's UBV data, transformed to UBV (unpublished)", Catalogue of Eggen's UBV Data, Bibcode:1986EgUBV........0M.
  3. Sato, Bun'ei; Omiya, Masashi; Harakawa, Hiroki; Liu, Yu-Juan; et al. (August 2013), "Planetary Companions to Three Evolved Intermediate-Mass Stars: HD 2952, HD 120084, and omega Serpentis", Publications of the Astronomical Society of Japan, 65 (4): 12, arXiv:1304.4328, Bibcode:2013PASJ...65...85S, doi:10.1093/pasj/65.4.85, 85.
  4. Jofré, E.; et al. (2015), "Stellar parameters and chemical abundances of 223 evolved stars with and without planets", Astronomy & Astrophysics, 574: A50, arXiv:1410.6422, Bibcode:2015A&A...574A..50J, doi:10.1051/0004-6361/201424474, A50.
  5. "ome Ser". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-03-23.
  6. Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x.
  7. Chupina, N. V.; et al. (June 2006), "Kinematic structure of the corona of the Ursa Major flow found using proper motions and radial velocities of single stars", Astronomy and Astrophysics, 451 (3): 909–916, Bibcode:2006A&A...451..909C, doi:10.1051/0004-6361:20054009.
  8. Puzeras, E.; et al. (October 2010), "High-resolution spectroscopic study of red clump stars in the Galaxy: iron-group elements", Monthly Notices of the Royal Astronomical Society, 408 (2): 1225–1232, arXiv:1006.3857, Bibcode:2010MNRAS.408.1225P, doi:10.1111/j.1365-2966.2010.17195.x.
  9. Sato, Bun'ei; et al. (February 2005), "Radial-Velocity Variability of G-Type Giants: First Three Years of the Okayama Planet Search Program", Publications of the Astronomical Society of Japan, 57 (1): 97–107, Bibcode:2005PASJ...57...97S, doi:10.1093/pasj/57.1.97.
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