Beta1 Sagittarii

Beta1 Sagittarii, Latinized from β1 Sagittarii, is a binary star system in the zodiac constellation of Sagittarius,[11] next to the southern constellation border with Telescopium. The brighter primary is named Arkab Prior /ˈɑːrkæb ˈpraɪər/, the traditional name of the system.[12][13] It is visible to the naked eye with a combined apparent visual magnitude of +4.01.[2] Based upon an annual parallax shift of 10.40 mas as seen from Earth,[1] it is located roughly 310 light-years from the Sun. At Beta¹ Sagittarii's distance, the visual magnitude is diminished by an extinction factor of 0.17 due to interstellar dust.[9]

For other stars with this Bayer designation, see β Sagittarii.
Beta¹ Sagittarii
Location of β Sagittarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 19h 22m 38.29770s[1]
Declination −44° 27′ 32.2458″[1]
Apparent magnitude (V) +4.01[2]
Characteristics
Spectral type B9 V + A5 V[3][4]
U−B color index −0.39[2]
B−V color index −0.10[2]
Astrometry
Radial velocity (Rv)−10.7±2.7[5] km/s
Proper motion (μ) RA: +13.67[1] mas/yr
Dec.: −19.03[1] mas/yr
Parallax (π)10.40 ± 1.14[1] mas
Distanceapprox. 310 ly
(approx. 100 pc)
Absolute magnitude (MV)−1.32[6]
Details
β¹ Sgr A
Mass3.67±0.14[7] M☉
Radius2.73[4] R☉
Luminosity324[7] L☉
Surface gravity (log g)3.83[8] cgs
Temperature11,960[8] K
Metallicity [Fe/H]−0.35[8] dex
Rotational velocity (v sin i)85±13[4] km/s
Age224[9] Myr
β¹ Sgr B
Radius1.89[4] R☉
Rotational velocity (v sin i)140±21[4] km/s
Other designations
Arkab Prior, β1 Sgr, CD−44° 13277, FK5 1502, HD 181454, HIP 95241, HR 7337, SAO 229646, WDS J19226-4428A[10]
Database references
SIMBADdata

The pair of stars that constitute this system have an angular separation of 28.3[11] arc seconds, with an estimated physical separation of about 3,290 AU.[4] The primary, Beta1 Sagittarii A, is a B-type main sequence star with a stellar classification of B9 V.[3][4] It is about 95% of the way through its lifespan on the main sequence.[7] The star has around 3.7[7] times the mass of the Sun and 2.7[4] times the Sun's radius. It is an estimated 224[9] million years old and is spinning with a projected rotational velocity of 85 km/s.[4] The star is radiating 324[7] times the luminosity of the Sun from its photosphere at an effective temperature of 11,960 K.[8]

The companion, Beta1 Sagittarii B, is a magnitude 7.4[11] A-type main sequence star with a class of A5 V.[3] It has 1.89[4] times the radius of the Sun and may be spinning faster than the primary with a projected rotational velocity of 140 km/s.[4]

Nomenclature

β¹ Sagittarii (Latinised to Beta¹ Sagittarii) is the system's Bayer designation. The designations of the two components as Beta¹ Sagittarii A and B derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[14]

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 Prior for Beta¹ 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, 天淵 (Tiān Yuān), meaning Celestial Spring, refers to an asterism consisting of Beta¹ Sagittarii, Beta² Sagittarii and Alpha Sagittarii. Consequently, the Chinese name for Beta¹ Sagittarii itself is 天淵二 (Tiān Yuān èr, English: the Second Star of Celestial Spring.)[17]

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. Nicolet, B. (1978), "Photoelectric photometric Catalogue of homogeneous measurements in the UBV System", Astronomy and Astrophysics Supplement Series, 34: 1–49, Bibcode:1978A&AS...34....1N.
  3. Levato, H. (1975), "Rotational velocities and spectral types for a sample of binary systems", Astronomy and Astrophysics, 19: 91, Bibcode:1975A&AS...19...91L.
  4. Howe, K. S.; Clarke, C. J. (January 2009), "An analysis of v sin (i) correlations in early-type binaries", Monthly Notices of the Royal Astronomical Society, 392 (1): 448–454, Bibcode:2009MNRAS.392..448H, doi:10.1111/j.1365-2966.2008.14073.x.
  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, S2CID 119231169.
  6. 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.
  7. Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
  8. Hempel, M.; Holweger, H. (September 2003), "Abundance analysis of late B stars. Evidence for diffusion and against weak stellar winds", Astronomy and Astrophysics, 408: 1065–1076, Bibcode:2003A&A...408.1065H, doi:10.1051/0004-6361:20030889.
  9. Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694–706, arXiv:1606.09028, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035, S2CID 119108982.
  10. "bet01 Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-07-07.
  11. 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.
  12. 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.
  13. Naming Stars, IAU.org, retrieved 16 December 2017.
  14. 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].
  15. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  16. "Bulletin of the IAU Working Group on Star Names, No. 2" (PDF). Retrieved 16 December 2017.
  17. (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 7 月 2 日
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