Gamma Hydri

γ Hydri, Latinised as Gamma Hydri, is a solitary,[9] red-hued star in the constellation Hydrus. It has an apparent visual magnitude of 3.26,[2] making it easily visible to the naked eye at night. Based upon an annual parallax shift of 15.24 mas as measured from Earth,[1] the system is located about 214 light years from the Sun.

Gamma Hydri
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydrus
Right ascension 03h 47m 14.34062s[1]
Declination −74° 14′ 20.2686″[1]
Apparent magnitude (V) 3.26[2]
Characteristics
Spectral type M1 III[3]
U−B color index +1.98[4]
B−V color index +1.62[4]
Astrometry
Radial velocity (Rv)+15.8±0.6[5] km/s
Proper motion (μ) RA: +50.85[1] mas/yr
Dec.: +114.74[1] mas/yr
Parallax (π)15.24 ± 0.11[1] mas
Distance214 ± 2 ly
(65.6 ± 0.5 pc)
Absolute magnitude (MV)−0.83[6]
Details[7]
Mass1.0 M☉
Radius62±1 R☉
Luminosity513 L☉
Surface gravity (log g)0.84 cgs
Temperature3499 K
Metallicity [Fe/H]0.0 dex
Other designations
γ Hyi, CD−74° 276, HD 24512, HIP 17678, HR 1208, SAO 256029[8]
Database references
SIMBADdata

This is an evolved red giant star with a stellar classification of M1 III,[3] and is most likely on the asymptotic giant branch of the HR diagram.[10] It is a semiregular variable that pulsates between magnitudes 3.26 and 3.33, although its period is not known precisely.[11] It has about the same mass as the Sun, but has expanded to around 62 times the Sun's radius. The star is radiating 513 times the Sun's luminosity from its enlarged photosphere at an effective temperature of 3,499 K.[7]

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, S2CID 18759600.
  2. Ducati, J. R. (2002), "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system", CDS/ADC Collection of Electronic Catalogues, 2237, Bibcode:2002yCat.2237....0D.
  3. Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.
  4. Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
  5. 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.
  6. Cardini, D. (January 2005), "Mg II chromospheric radiative loss rates in cool active and quiet stars", Astronomy and Astrophysics, 430: 303–311, arXiv:astro-ph/0409683, Bibcode:2005A&A...430..303C, doi:10.1051/0004-6361:20041440, S2CID 12136256.
  7. Cruzalèbes, P.; et al. (September 2013), "Fundamental parameters of 16 late-type stars derived from their angular diameter measured with VLTI/AMBER", Monthly Notices of the Royal Astronomical Society, 434 (1): 437–450, arXiv:1306.3288, Bibcode:2013MNRAS.434..437C, doi:10.1093/mnras/stt1037, S2CID 49573767.
  8. "gam Hyi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-18.
  9. 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, S2CID 14878976.
  10. Eggen, O. J. (1992), "Asymptotic giant branch stars near the sun", The Astronomical Journal, 104: 275, Bibcode:1992AJ....104..275E, doi:10.1086/116239.
  11. Tabur, V.; Bedding, T. R.; Kiss, L. L.; Moon, T. T.; Szeidl, B.; Kjeldsen, H. (2009), "Long-term Photometry and Periods for 261 Nearby Pulsating M Giants", Monthly Notices of the Royal Astronomical Society, 400 (4): 1945–61, arXiv:0908.3228, Bibcode:2009MNRAS.400.1945T, doi:10.1111/j.1365-2966.2009.15588.x, S2CID 15358380.
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