Omega Sagittarii

Omega Sagittarii, which is Latinized from ω Sagittarii, is a binary star system in the constellation of Sagittarius,[9] near the eastern constellation border with Capricornus. It is formally named Terebellum /tɛrɪˈbɛləm/.[10][11] This system has a yellow hue and is faintly visible to the naked eye with an apparent visual magnitude of 4.70.[2] It is located at a distance of 76 light years away from the Sun based on parallax,[1] and is drifting closer with a radial velocity of −16 km/s.[1] The position of this star near the ecliptic means it is subject to lunar occultations.[12]

Omega Sagittarii
Location of ω Sagittarii (circled)
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Sagittarius
Right ascension 19h 55m 50.36255s[1]
Declination −26° 17′ 57.6933″[1]
Apparent magnitude (V) 4.70[2]
Characteristics
Evolutionary stage subgiant
Spectral type G5 IV[3]
U−B color index +0.32[4]
B−V color index +0.748±0.015[1]
R−I color index +0.37[4]
Astrometry
Radial velocity (Rv)−16.22±0.43[1] km/s
Proper motion (μ) RA: 203.96[5] mas/yr
Dec.: 74.40[5] mas/yr
Parallax (π)42.7159 ± 0.5538[1] mas
Distance76.4 ± 1.0 ly
(23.4 ± 0.3 pc)
Absolute magnitude (MV)2.64[2]
Orbit[6]
Period (P)1,712.74±0.29 d
Semi-major axis (a)≥ 1.1044 ± 0.0051 AU
Eccentricity (e)0.8200±0.0012
Periastron epoch (T)57549.31±0.20 HJD
Argument of periastron (ω)
(secondary)		141.17±0.33°
Semi-amplitude (K1)
(primary)		12.255±0.041 km/s
Details[7]
Mass1.52+0.08
−0.06 M☉
Radius2.87+0.37
−0.34[1] R☉
Luminosity7.1±0.1[1] L☉
Surface gravity (log g)3.64±0.05 cgs
Temperature5,499±91 K
Metallicity [Fe/H]0.06±0.06 dex
Rotational velocity (v sin i)5.6[8] km/s
Age3.00+0.13
−0.61 Gyr
Other designations
Terebellum, ψ Sgr, 58 Sagittarii, CPD−26°6880, FK5 1629, GC 27583, HD 188376, HIP 98066, HR 7597, SAO 188722, PPM 270451[9]
Database references
SIMBADdata

The members of this system orbit each other with a period of 4.6892 yr and an eccentricity of 0.82.[6] The visible component is a G-type subgiant star with a stellar classification of G5 IV.[3] It is three[7] billion years old and is spinning with a projected rotational velocity of 5.6 km/s.[8] The star is radiating seven[1] times the luminosity of the Sun from its photosphere at an effective temperature of 5,499 K.[7]

Nomenclature
The four stars of the Terebellum

ω Sagittarii (Latinised to Omega Sagittarii) is the star's Bayer designation.

This star, together with 60, 62 and 59 Sagittarii, formed the asterism called Terebellum.[13] According to a 1971 NASA memorandum, Terebellum was originally the title for four stars: Omega Sagittarii as Terebellum I, 59 Sagittarii as Terebellum II, 60 Sagittarii as Terebellum III and 62 Sagittarii as Terebellum IV .[14] In 2016, the IAU organized a Working Group on Star Names (WGSN)[15] to catalog and standardize proper names for stars. The WGSN approved the name Terebellum for Omega Sagittarii on 5 September 2017 and it is now so included in the List of IAU-approved Star Names.[10]

In Chinese, 狗國 (Gǒu Guó), meaning Dog Territory, refers to an asterism consisting of Omega Sagittarii, 60 Sagittarii, 62 Sagittarii and 59 Sagittarii. Consequently, the Chinese name for Omega Sagittarii itself is 狗國一 (Gǒu Guó yī, English: the First Star of Dog Territory.)[16]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. 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.
  3. Keenan, Philip C.; McNeil, Raymond C. (1989), "The Perkins catalog of revised MK types for the cooler stars", Astrophysical Journal Supplement Series, 71: 245, Bibcode:1989ApJS...71..245K, doi:10.1086/191373.
  4. Hoffleit, D.; Warren, Jr., W. H., The Bright Star Catalogue (5th Revised ed.), CDS ID V/50. HR 7597 Archived 2016-03-04 at the Wayback Machine, database entry. Accessed on line November 19, 2009.
  5. Van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653, arXiv:0708.1752, Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357.
  6. Fekel, Francis C.; et al. (September 2018), "Spectroscopic Orbits for Late-type Stars. II", The Astronomical Journal, 156 (3): 15, Bibcode:2018AJ....156..117F, doi:10.3847/1538-3881/aad3c1, 117.
  7. Aguilera-Gómez, Claudia; et al. (June 2018), "Lithium abundance patterns of late-F stars: an in-depth analysis of the lithium desert", Astronomy & Astrophysics, 614: 15, arXiv:1803.05922, Bibcode:2018A&A...614A..55A, doi:10.1051/0004-6361/201732209, A55.
  8. Luck, R. Earle (January 2017), "Abundances in the Local Region II: F, G, and K Dwarfs and Subgiants", The Astronomical Journal, 153 (1): 19, arXiv:1611.02897, Bibcode:2017AJ....153...21L, doi:10.3847/1538-3881/153/1/21, 21.
  9. "ome Sgr". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2019-10-28.
  10. "Naming Stars". IAU.org. Retrieved 16 December 2017.
  11. "Terebella". Oxford English Dictionary (Online ed.). Oxford University Press. (Subscription or participating institution membership required.)
  12. Evans, David S.; et al. (November 1986), "Photoelectric observations of lunar occultations. XVI.", Astronomical Journal, 92: 1210–1215, Bibcode:1986AJ.....92.1210E, doi:10.1086/114254, hdl:2152/34378.
  13. Allen, R. H. (1963). Star Names: Their Lore and Meaning (Reprint ed.). New York: Dover Publications Inc. p. 355. ISBN 0-486-21079-0. Retrieved 2012-09-04.
  14. Rhoads, Jack W. (November 15, 1971), Technical Memorandum 33-507-A Reduced Star Catalog Containing 537 Named Stars (PDF), California Institute of Technology: Jet Propulsion Laboratory, retrieved 2019-10-28.
  15. "IAU Working Group on Star Names (WGSN)". Retrieved 22 May 2016.
  16. (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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