Gamma Capricorni

Gamma Capricorni or γ Capricorni, formally named Nashira (/ˈnæʃɪrə/),[12] is a giant star in the constellation of Capricornus. Based on parallax measurements obtained during the Hipparcos mission, it is located at a distance of approximately 157 light-years from the Sun. The star is drifting closer with a radial velocity of −31 km/s.[6] It is 2.56 degrees south of the ecliptic, so it can be occulted by the Moon, and (rarely) by planets.

γ Capricorni
Location of γ Capricorni (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Capricornus
Right ascension 21h 40m 05.45648s[1]
Declination −16° 39′ 44.307184″[1]
Apparent magnitude (V) +3.67[2]
Characteristics
Spectral type kF0hF1VmF2[3]
U−B color index +0.22[4]
B−V color index +0.32[4]
Variable type α2 CVn[5]
Astrometry
Radial velocity (Rv)−31.2±0.5[6] km/s
Proper motion (μ) RA: +187.56[1] mas/yr
Dec.: −22.45[1] mas/yr
Parallax (π)20.77 ± 0.72 mas[1]
Distance157 ± 5 ly
(48 ± 2 pc)
Absolute magnitude (MV)+2.60[7]
Details
Mass2.44[8] M☉
Radius2.35[8] R☉
Surface gravity (log g)3.69[8] cgs
Temperature7,520[9] K
Metallicity [Fe/H]+0.5[9] dex
Rotational velocity (v sin i)40[10] km/s
Other designations
Nashira, Gamma Cap, Gam Cap, γ Cap, 40 Capricorni, BD−17°6340, FK5 812, GJ 4209, HD 206088, HIP 106985, HR 8278, SAO 164560[11]
Database references
SIMBADdata

Nomenclature

γ Capricorni (Latinised to Gamma Capricorni) is the star's Bayer designation.

It bore the traditional name Nashira, derived from the Arabic سعد ناشرة sa'd nashirah "the lucky one" or "bearer of good news". In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[13] to catalogue and standardize proper names for stars. The WGSN approved the name Nashira for this star on 21 August 2016 and it is now so included in the List of IAU-approved Star Names.[12]

In Chinese, 壘壁陣 (Lěi Bì Zhèn), meaning Line of Ramparts, refers to an asterism consisting of Gamma Capricorni, Kappa Capricorni, Epsilon Capricorni, Delta Capricorni, Iota Aquarii, Sigma Aquarii, Lambda Aquarii, Phi Aquarii, 27 Piscium, 29 Piscium, 33 Piscium and 30 Piscium.[14] Consequently, the Chinese name for Gamma Capricorni itself is 壘壁陣三 (Lěi Bì Zhèn sān, English: the Third Star of Line of Ramparts).[15]

Namesake

Nashira (AK-85) was a United States Navy ship, though it was never commissioned and never bore the USS designation.[16][17]

Properties

γ Capricorni is classified as a hot chemically peculiar Am star with a mean apparent magnitude of +3.67. The spectrum displays abundance anomalies of the elements strontium, chromium, and europium.[8] It was first classified as an Am star in 1965 by K. Osawa, but in 1974 C. Bertaud and M. Floquet found it to be an Ap star with a strontium abundance anomaly. In 1998, F. A. Catalano and associates found a slight variability in the infrared J band with a period of 2.78 days, which suggests the Ap classification is correct. However, no magnetic field is detected, which points to the Am classification, as does the infrared spectrum. The star displays large radial velocity variations, which could be explained by star spots and rotation. Alternatively it may be a double-lined spectroscopic binary viewed from nearly pole-on.[18]

This star is classified as an α2 Canum Venaticorum type variable star and its brightness varies by 0.03 magnitudes.[5] It has 2.44 times the mass and 2.35 times the radius of the Sun.[8] O. J. Eggen included it as a member of the Hyades Stream.[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. Abt, Helmut A.; Morrell, Nidia I. (1995). "The Relation between Rotational Velocities and Spectral Peculiarities among A-Type Stars". Astrophysical Journal Supplement. 99: 135. Bibcode:1995ApJS...99..135A. doi:10.1086/192182.
  4. Johnson, H. L.; Iriarte, B.; Mitchell, R. I.; Wisniewskj, W. Z. (1966). "UBVRIJKL photometry of the bright stars". Communications of the Lunar and Planetary Laboratory. 4 (99): 99. Bibcode:1966CoLPL...4...99J.
  5. Samus, N. N.; Durlevich, O. V.; et al. (2009). "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)". VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S. 1. Bibcode:2009yCat....102025S.
  6. Gontcharov, G. A. (November 2006). "Pulkovo Compilation of Radial Velocities for 35495 Hipparcos stars in a common system". Astronomy Letters. 32 (11): 759–771. arXiv:1606.08053. Bibcode:2006AstL...32..759G. doi:10.1134/S1063773706110065. S2CID 119231169.
  7. Eggen, Olin J. (July 1998), "The Age Range of Hyades Stars", The Astronomical Journal, 116 (1): 284–292, Bibcode:1998AJ....116..284E, doi:10.1086/300413.
  8. Glagolevskij, Yu. V. (January 2019). "On Properties of Main Sequence Magnetic Stars". Astrophysical Bulletin. 74 (1): 66–79. Bibcode:2019AstBu..74...66G. doi:10.1134/S1990341319010073. S2CID 149900274.
  9. Burkhart, C.; Coupry, M. F. (September 1991). "The A and Am-Fm stars. I - The abundances of Li, Al, Si, and Fe". Astronomy and Astrophysics. 249 (1): 205–216. Bibcode:1991A&A...249..205B.
  10. Royer, F.; Grenier, S.; Baylac, M.-O.; Gómez, A. E.; Zorec, J. (October 2002). "Rotational velocities of A-type stars in the northern hemisphere. II. Measurement of v sin i". Astronomy and Astrophysics. 393 (3): 897–911. arXiv:astro-ph/0205255. Bibcode:2002A&A...393..897R. doi:10.1051/0004-6361:20020943. S2CID 14070763.
  11. "gam Cap". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2021-06-20.
  12. "Naming Stars". IAU.org. Retrieved 7 March 2018.
  13. IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  14. (in Chinese) 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, ISBN 978-986-7332-25-7.
  15. (in Chinese) 香港太空館 - 研究資源 - 亮星中英對照表 Archived January 30, 2011, at the Wayback Machine, Hong Kong Space Museum. Accessed on line November 23, 2010.
  16. "Ship Naming in the United States Navy". Naval History & Heritage Command. Archived from the original on 3 January 2015.
  17. "NavSource Online: Service Ship Photo Archive: AK-85 Nashira". navsource.org. Retrieved 28 December 2016.
  18. Carrier, F.; North, P.; Udry, S.; Babel, J. (October 2002). "Multiplicity among chemically peculiar stars. II. Cool magnetic Ap stars". Astronomy and Astrophysics. 394: 151–169. arXiv:astro-ph/0208082. Bibcode:2002A&A...394..151C. doi:10.1051/0004-6361:20021122. S2CID 14223227.
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