HD 117939

HD 117939 is a Sun-like star in the southern constellation of Centaurus. With an apparent visual magnitude of 7.29[2] it is too faint to be viewed with the naked eye, but is within the range of binoculars or a small telescope. It is located at a distance of 98.5 light years from the Sun based on parallax measurements,[2] and is drifting further away with a radial velocity of +82 km/s.[1] This is an intermediate disk[5] star with a high proper motion, traversing the celestial sphere at an angular rate of 0.68 arcsec yr−1.[8]

HD 117939
Observation data
Epoch J2000      Equinox J2000
Constellation Centaurus
Right ascension 13h 34m 32.64985s[1]
Declination −38° 54′ 25.9664″[1]
Apparent magnitude (V) 7.29[2]
Characteristics
Evolutionary stage Main sequence
Spectral type G4V[3]
B−V color index 0.669±0.006[2]
Astrometry
Radial velocity (Rv)+82.09±0.17[1] km/s
Proper motion (μ) RA: 446.17[4] mas/yr
Dec.: −394.11[4] mas/yr
Parallax (π)33.1143 ± 0.0431 mas[1]
Distance98.5 ± 0.1 ly
(30.20 ± 0.04 pc)
Absolute magnitude (MV)4.90[2]
Details
Mass0.92[5] M☉
Radius1.01±0.04[5] R☉
Luminosity1.095±0.002[1] L☉
Surface gravity (log g)4.42±0.06[6] cgs
Temperature5,765±40[6] K
Metallicity [Fe/H]−0.22±0.07[5] dex
Rotational velocity (v sin i)1.0±1.0[5] km/s
Age6.1[6] Gyr
Other designations
CD−38° 8635, GJ 9450, HD 117939, HIP 66238, SAO 204606, LHS 2760[7]
Database references
SIMBADdata

An ordinary G-type main-sequence star with a stellar classification of G4V,[3] this star is an "excellent photometric match for the Sun";[6] the atmospheric properties of the star make it a near solar twin. It is older than the sun at 6.1 billion years, but is more chromospherically active.[6]

To date no exact solar twin (precisely matching all important properties of the Sun) has been found. However, there are some stars that come very close to being identical to the Sun, and as such are dubbed solar twins by astronomers. An exact solar twin would be a 4.6 billion years old G2V star with a 5,778K temperature, the correct metallicity, and a 0.1% solar luminosity variation.[9] G2V stars with an age of 4.6 billion years or more have typically reached their most stable state. Proper metallicity and size are also important to low luminosity variation.[10][11]

Sun comparison

Chart compares the sun to HD 117939.

Identifier Stellar
Class		 Temperature
(K)		 Metallicity
(dex)		 Age
(Gyr)		 Notes
Sun G2V 5,778 +0.00 4.6 [12]
HD 117939 G4V 5,765 −0.22 6.1 [6][5]

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. Gray, R. O.; et al. (July 2006). "Contributions to the Nearby Stars (NStars) Project: spectroscopy of stars earlier than M0 within 40 pc-The Southern Sample". The Astronomical Journal. 132 (1): 161–170. arXiv:astro-ph/0603770. Bibcode:2006AJ....132..161G. doi:10.1086/504637. S2CID 119476992.
  4. 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. S2CID 18759600.
  5. Fuhrmann, Klaus; Chini, Rolf (January 2019). "On ancient solar-type stars". Monthly Notices of the Royal Astronomical Society. 482 (1): 471–489. Bibcode:2019MNRAS.482..471F. doi:10.1093/mnras/sty2660.
  6. Porto de Mello, G. F.; et al. (March 2014). "A photometric and spectroscopic survey of solar twin stars within 50 parsecs of the Sun. I. Atmospheric parameters and color similarity to the Sun". Astronomy & Astrophysics. 563: 25. arXiv:1312.7571. Bibcode:2014A&A...563A..52P. doi:10.1051/0004-6361/201322277. S2CID 119111150. A52.
  7. "HD 117939". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2016-09-26.
  8. Bakos, Gáspár Á.; et al. (July 2002). "Revised Coordinates and Proper Motions of the Stars in the Luyten Half-Second Catalog". The Astrophysical Journal Supplement Series. 141 (1): 187–193. arXiv:astro-ph/0202164. Bibcode:2002ApJS..141..187B. doi:10.1086/340115. S2CID 36667868.
  9. "Solar Variability and Terrestrial Climate". Science News. NASA. January 8, 2013.
  10. "Stellar Luminosity Calculator". University of Nebraska-Lincoln astronomy education group.
  11. "The Effects of Solar Variability on Earth's Climate, 2012 Report". National Center for Atmospheric Research.
  12. Williams, D. R. (2004). "Sun Fact Sheet". NASA. Retrieved 2009-06-23.
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