Beta2 Sagittarii
Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
---|---|
Constellation | Sagittarius |
Right ascension | 19h 23m 13.13745s[1] |
Declination | −44° 47′ 59.2051″[1] |
Apparent magnitude (V) | +4.29[2] |
Characteristics | |
Spectral type | F2/3 V[3] or F2 III[4] |
U−B color index | +0.07[2] |
B−V color index | +0.34[2] |
Astrometry | |
Radial velocity (Rv) | +19.0[5] km/s |
Proper motion ( | RA: +93.45[1] mas/yr Dec.: −54.09[1] mas/yr |
Parallax ( | 24.31 ± 0.19 mas[1] |
Distance | 134 ± 1 ly (41.1 ± 0.3 pc) |
Absolute magnitude (MV) | +1.20[6] |
Details | |
Mass | 1.43[7] M☉ |
Luminosity | 20[8] L☉ |
Surface gravity (log g) | 3.57[7] cgs |
Temperature | 7,035±239[7] K |
Metallicity [Fe/H] | −0.54[5] dex |
Rotational velocity (v sin i) | 155[9] km/s |
Age | 933[7] Myr |
Other designations | |
Database references | |
SIMBAD | data |
Beta2 Sagittarii (
Based upon variations in its proper motion, this is a probable astrometric binary system.[11] As such, its two components would be designated Beta2 Sagittarii A (officially named Arkab Posterior /ˈɑːrkæb pɒˈstɪəriər/, the traditional name of the system)[12][13] and B.
Nomenclature
[edit]In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN approved the name Arkab Posterior for Beta2 Sagittarii on 5 October 2016 and it is now so included in the List of IAU-approved Star Names.[13] For such names relating to members of multiple star systems, and where a component letter (from e.g. Washington Double Star Catalog) is not explicitly listed, the WGSN says that the name should be understood to be attributed to the brightest component by visual brightness.[16]
In Chinese,
Properties
[edit]Houk (1978) categorizes the visible component (Beta2 Sagittarii A) as an F-type main-sequence star with a stellar classification of F2/3 V.[3] However, Malaroda (1975) lists it as an F-type giant star.[4] It is spinning rapidly with a projected rotational velocity of 155 km/s. This is giving it an oblate shape with an equatorial bulge that is 22% larger than the polar radius.[9] Beta2 Sagittarii has an estimated 1.4[7] times the mass of the Sun and is around 933[7] million years old.
References
[edit]- ^ a b c d e f 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.
- ^ a b c d 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.
- ^ a b Houk, Nancy (1978), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 2, Ann Arbor: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.
- ^ a b Malaroda, S. (August 1975), "Study of the F-type stars. I. MK spectral types", Astronomical Journal, 80: 637–641, Bibcode:1975AJ.....80..637M, doi:10.1086/111786.
- ^ a b Casagrande, L.; et al. (2011), "New constraints on the chemical evolution of the solar neighbourhood and Galactic disc(s). Improved astrophysical parameters for the Geneva-Copenhagen Survey", Astronomy & Astrophysics, 530 (A138): 21, arXiv:1103.4651, Bibcode:2011A&A...530A.138C, doi:10.1051/0004-6361/201016276, S2CID 56118016.
- ^ 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.
- ^ a b c d e f David, Trevor J.; Hillenbrand, Lynne A. (2015), "The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets", The Astrophysical Journal, 804 (2): 146, arXiv:1501.03154, Bibcode:2015ApJ...804..146D, doi:10.1088/0004-637X/804/2/146, S2CID 33401607.
- ^ McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x, S2CID 118665352.
- ^ a b Belle, G. T. (2012), "Interferometric observations of rapidly rotating stars", The Astronomy and Astrophysics Review, 20 (1): 51, arXiv:1204.2572, Bibcode:2012A&ARv..20...51V, doi:10.1007/s00159-012-0051-2, S2CID 119273474.
- ^ "bet02 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-10.
- ^ 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.
- ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
- ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
- ^ Hessman, F. V.; Dhillon, V. S.; Winget, D. E.; Schreiber, M. R.; Horne, K.; Marsh, T. R.; Guenther, E.; Schwope, A.; Heber, U. (2010). "On the naming convention used for multiple star systems and extrasolar planets". arXiv:1012.0707 [astro-ph.SR].
- ^ "I
AU Working Group on Star Names (WGSN)". Retrieved 22 May 2016. - ^ "Bulletin of the I
AU Working Group on Star Names, No. 2" (PDF). Retrieved 16 December 2017. - ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy)
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