| absmag_v = +1.20[12]
}}{{Starbox detail
| source =
| mass = 1.43[13]
| radius =
| luminosity = 20[14]
| temperature = {{Val|7035|239|fmt=commas}}[13]
| gravity = 3.57[13]
| metal_fe = −0.54[8]
| rotational_velocity = 155[18]
| age_myr = 933[13]
}}{{Starbox catalog
| names = {{odlist | name=Arkab Posterior | B=β² Sgr | CD=−45° 13171 | HD=181623 | HIP=95294 | HR=7343 | SAO=229654 }}[20]
}}{{Starbox reference
| Simbad = bet02+Sgr
}}{{Starbox end}}Beta² Sagittarii (β² Sagittarii, abbreviated Beta² Sgr, β² Sgr) is a star in the zodiac constellation of Sagittarius. It is visible to the naked eye, having an apparent visual magnitude of +4.29.[3] Based upon an annual parallax shift of 24.31 mas as seen from Earth,[ it is located 134 light-years from the Sun.]
Based upon variations in its proper motion, this is a probable astrometric binary system.[23] As such, its two components would be designated Beta² Sagittarii A (also named Arkab Posterior[1]) and B
Nomenclature
β² Sagittarii (Latinised to Beta² Sagittarii) is the system's Bayer designation. The designations of the two components as Beta² 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).[2]In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN)[3] 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.[1] 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.[4]
In Chinese, {{lang|zh|天淵}} ({{lang|zh-Latn|Tiān Yuān}}), meaning Celestial Spring, refers to an asterism consisting of Beta² Sagittarii, Beta¹ Sagittarii and Alpha Sagittarii. Consequently, Beta² Sagittarii itself is known as {{lang|zh|天淵一}} ({{lang|zh-Latn|Tiān Yuān yī}}, {{lang-en|the First Star of Celestial Spring}}.)[5]
Properties
Houk (1978) categorizes the visible component (Beta² Sagittarii A) as an F-type main-sequence star with a stellar classification of F2/3 V.[4] However, Malaroda (1975) lists it as an F-type giant star.[5] 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.[18] Beta² Sagittarii has an estimated 1.4[13] times the mass of the Sun and is around 933[13] million years old.
References
1. ^1 {{cite web | url=https://www.iau.org/public/themes/naming_stars/ | title=Naming Stars |publisher=IAU.org |accessdate=16 December 2017}}
2. ^{{cite arXiv |title=On the naming convention used for multiple star systems and extrasolar planets |date=2010 |eprint=1012.0707 |class=astro-ph.SR |last1= Hessman |first1=F. V. |last2= Dhillon |first2=V. S. |last3= Winget |first3=D. E. |last4= Schreiber |first4=M. R. |last5= Horne |first5=K. |last6= Marsh |first6=T. R. |last7= Guenther |first7=E. |last8= Schwope |first8=A. |last9= Heber |first9=U. }}
3. ^{{cite web | url=https://www.iau.org/science/scientific_bodies/working_groups/280/ | title=IAU Working Group on Star Names (WGSN)|accessdate=22 May 2016}}
4. ^{{cite web | url=http://www.pas.rochester.edu/~emamajek/WGSN/WGSN_bulletin2.pdf | title=Bulletin of the IAU Working Group on Star Names, No. 2 |accessdate=16 December 2017}}
5. ^{{zh icon}} 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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11. ^1 2 3 4 5 6 {{citation | last1=David | first1=Trevor J. | last2=Hillenbrand | first2=Lynne A. | title=The Ages of Early-Type Stars: Strömgren Photometric Methods Calibrated, Validated, Tested, and Applied to Hosts and Prospective Hosts of Directly Imaged Exoplanets | journal=The Astrophysical Journal | volume=804 | issue=2 | pages=146 | year=2015 | bibcode=2015ApJ...804..146D | doi=10.1088/0004-637X/804/2/146 | arxiv=1501.03154 | postscript=. }}
12. ^1 2 {{citation | last1=Houk | first1=Nancy | title=Michigan catalogue of two-dimensional spectral types for the HD stars | volume=2 | publication-place=Ann Arbor | publisher=Dept. of Astronomy, University of Michigan | year=1978 | bibcode=1978mcts.book.....H | postscript=. }}
13. ^1 2 {{citation | last=Malaroda | first=S. | title=Study of the F-type stars. I. MK spectral types | journal=Astronomical Journal | postscript=. | volume=80 | pages=637–641 |date=August 1975 | doi=10.1086/111786 | bibcode=1975AJ.....80..637M }}
14. ^1 2 3 4 {{citation | display-authors=1 | last1=Johnson | first1=H. L. | last2=Iriarte | first2=B. | last3=Mitchell | first3=R. I. | last4=Wisniewskj | first4=W. Z. | title=UBVRIJKL photometry of the bright stars | journal=Communications of the Lunar and Planetary Laboratory | volume=4 | issue=99 | year=1966 | bibcode=1966CoLPL...4...99J | postscript=. }}
15. ^1 {{cite simbad | title=bet02 Sgr | accessdate=2017-07-10 | postscript=. }}