Gamma Coronae Australis

Gamma Coronae Australis (γ CrA), is a binary star located in the constellation Corona Australis. The system has a combined apparent visual magnitude of 4.20,[2] making it faintly visible to the naked eye. It is located 56.4 light-years (17.3 parsecs) from the Sun, based on its parallax.[1] Gamma Coronae Australis is a member of the Milky Way's thin disk.[6]

γ Coronae Australis
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Corona Australis
Right ascension  19h 06m 25.11014s[1]
Declination −37° 03′ 48.3901″[1]
Apparent magnitude (V) 4.20[2]
Characteristics
Spectral type F8V + F8V[3]
U−B color index +0.51[4]
B−V color index +0.01[4]
Astrometry
Radial velocity (Rv)−51.60 ± 0.3[5] km/s
Proper motion (μ) RA: 96.74 ± 1.05[1] mas/yr
Dec.: −281.71 ± 0.58[1] mas/yr
Parallax (π)57.79 ± 0.75[1] mas
Distance56.4 ± 0.7 ly
(17.3 ± 0.2 pc)
Absolute magnitude (MV)3.73 / 3.80[6]
Orbit[7]
Period (P)121.76 yr
Semi-major axis (a)1.896″
Eccentricity (e)0.320
Inclination (i)149.6°
Longitude of the node (Ω)50.3°
Periastron epoch (T)2000.64
Argument of periastron (ω)
(secondary)		349.0°
Details[6]
γ CrA A
Mass1.15 M☉
Radius1.47 R☉
Surface gravity (log g)4.17 cgs
Temperature6,090 K
Metallicity [Fe/H]−0.07 dex
Age5 Gyr
γ CrA B
Mass1.14 M☉
Radius1.42 R☉
Surface gravity (log g)4.19 cgs
Temperature6,100 K
Age5 Gyr
Other designations
γ CrA, CD−37° 13048, HIP 93825, SAO 210928, CCDM J19064-3704AB[2]
γ CrA A: HD 177474, HR 7226[8]
γ CrA B: HD 177475, HR 7227[9]
Database references
SIMBADγ CrA
γ CrA A
γ CrA B

The system is a visual binary, where the orbit is calculated from observations of one star orbiting the other. The primary, Gamma Coronae Australis A, is a late F-type main-sequence star with an effective temperature of 6,090 K.[6] It has an absolute an absolute magnitude of +3.73, and a mass of 1.15 solar masses.[6] The secondary, Gamma Coronae Australis B, is also F-type. With an effective temperature of 6,100 K, an absolute magnitude of +3.80, and a mass of 1.14 solar masses, the companion is almost identical to the primary.[6] Gamma Coronae Australis has been known to be a binary for a long time, and its two components have been given Henry Draper Catalogue designations of HD 177474[8] and HD 177475,[9] respectively. The two stars are separated by 1.896″ and orbit each other every 121.76 years.[7]

References
  1. van Leeuwen, F. (November 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. "* gam CrA". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 June 2017.
  3. Eggl, S.; Pilat-Lohinger, E.; Funk, B.; Georgakarakos, N.; Haghighipour, N. (2012). "Circumstellar habitable zones of binary-star systems in the solar neighbourhood". Monthly Notices of the Royal Astronomical Society. 428 (4): 3104. arXiv:1210.5411. Bibcode:2013MNRAS.428.3104E. doi:10.1093/mnras/sts257.
  4. Mermilliod, J.-C. (1986). "Compilation of Eggen's UBV data, transformed to UBV (unpublished)". Catalogue of Eggen's UBV Data. Bibcode:1986EgUBV........0M.
  5. Gontcharov, G. A. (2006). "Pulkovo Compilation of Radial Velocities for 35 495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065.
  6. Fuhrmann, K.; Chini, R. (2015). "Multiplicity Among F-Type Stars. II". The Astrophysical Journal. 809: 107. Bibcode:2015ApJ...809..107F. doi:10.1088/0004-637X/809/1/107.
  7. "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory. Retrieved 20 June 2017.
  8. "* gam CrA A". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 June 2017.
  9. "* gam CrA B". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 20 June 2017.
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