Zeta Sagittarii

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ζ Sagittarii
Location of ζ Sagittarii (circled)
Observation data
J2000.0
Constellation Sagittarius
Right ascension 19h 02m 36.73024s[1]
Declination –29° 52′ 48.2279″[1]
Apparent magnitude (V) +2.59[2] (3.27/3.48)[3]
Characteristics
Spectral type A2.5 Va[4]
U−B color index +0.05[2]
B−V color index +0.08[2]
Distance
88 ± 2 ly
(27.0 ± 0.6 pc)
Absolute magnitude (MV)1.11/1.32[3]
Argument of periastron
(ω)
(secondary)		7.2 ± 0.6°
Details
Myr
Other designations
Ascella, ζ Sagittarii, ζ Sgr, Zeta Sgr, 38 Sagittarii, CCDM J19026-2953AB, CPD-30  5798, GC 26161, HD 176687, HIP 93506, HR 7194, IDS 18562-3001 AB, PPM 269230, SAO 187600, WDS J19026-2953AB
Database references
SIMBADdata

Zeta Sagittarii (ζ Sagittarii, abbreviated Zeta Sgr, ζ Sgr) is a triple star system and the third-brightest star in the constellation of Sagittarius after Kaus Australis and Nunki. Based upon parallax measurements, it is about 88 light-years (27 parsecs) from the Sun.[1]

The three components are designated Zeta Sagittarii A (officially named Ascella /əˈsɛlə/, the traditional name for the entire system)[8][9] and B, themselves forming a binary pair, and a smaller companion star, C.

Nomenclature

ζ Sagittarii (Latinised to Zeta Sagittarii) is the system's Bayer designation. The designations of the three components as ζ Sagittarii A, B and C derive from the convention used by the Washington Multiplicity Catalog (WMC) for multiple star systems, and adopted by the International Astronomical Union (IAU).[10]

It bore the traditional name Ascella, from a

multiple systems.[13] It approved the name Ascella for the component Zeta Sagittarii A on 12 September 2016 and it is now so included in the List of IAU-approved Star Names.[9]

This star, together with Gamma Sagittarii, Delta Sagittarii, Epsilon Sagittarii, Lambda Sagittarii, Sigma Sagittarii, Tau Sagittarii and Phi Sagittarii comprise the Teapot asterism.[14]

In

Chinese name for Zeta Sagittarii itself is 斗宿一 (Dǒu Sù yī, English: the First Star of Dipper).[15]

Properties

Zeta Sagittarii has a combined

apparent visual magnitude of +2.59.[2] It is moving away from the Solar System with a radial velocity of 22 km s−1,[5] and some 1.0–1.4 million years ago, came within 7.5 ± 1.8 ly (2.30 ± 0.55 pc) of the Sun.[16]

The two components Zeta Sagittarii A and B

spectral class A2 giant with an apparent magnitude of +3.27, and B is an A4 subgiant with apparent magnitude of +3.48. The pair have a mean separation of 13.4 AU.[17]

The binary pair have a faint, 10th-magnitude companion, C, separated from them by a distance of 75

arcseconds
.

Zeta Sagittarii was the brightest star in the night sky around 1.2 million years ago,[18] peaking with an apparent magnitude of -2.74.[18]

References

  1. ^
    S2CID 18759600
  2. ^
    Bibcode:1966CoLPL...4...99J
    .
  3. ^
    S2CID 102487103
  4. ^ "* zet Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2012-02-18.
  5. ^
    Bibcode:1953GCRV..C......0W
    .
  6. ^
    S2CID 119417105
  7. S2CID 18475298
  8. Bibcode:1944PA.....52....8D
    .
  9. ^ a b "Naming Stars". IAU.org. Retrieved 16 December 2017.
  10. arXiv:1012.0707 [astro-ph.SR
    ].
  11. doi:10.1093/mnras/55.8.429
    .
  12. ^ IAU Working Group on Star Names (WGSN), International Astronomical Union, retrieved 22 May 2016.
  13. ^ "WG Triennial Report (2015-2018) - Star Names" (PDF). p. 5. Retrieved 2018-07-14.
  14. ^ "Teapot". constellation-guide.com. Retrieved 2017-05-13.
  15. ^ (in Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日
  16. doi:10.1051/0004-6361:20054284
  17. ^ Kaler, James B., "ASCELLA (Zeta Sagittarii)", Stars, University of Illinois, retrieved 2012-02-18
  18. ^
    HIPPARCOS data. (The calculations exclude stars whose distance or proper motion is uncertain.) PDF[permanent dead link
    ]
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