Gamma2 Sagittarii

γ² Sagittarii

Location of γ^2 Sagittarii (circled)
Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Sagittarius
Right ascension	18^h 05^m 48.48810^s[1]
Declination	–30° 25′ 26.7235″[1]
Apparent magnitude (V)	+2.98[2]
Characteristics
Spectral type	K1 III[2]
U−B color index	+0.77[3]
B−V color index	+1.01[3]
Astrometry
Radial velocity (Rv)	22.0[2] km/s
Proper motion (μ)	RA: –53.92[1] mas/yr Dec.: -180.90[1] mas/yr
Parallax (π)	33.67 ± 0.18[1] mas
Distance	96.9 ± 0.5 ly (29.7 ± 0.2 pc)
Details
Radius	12[4] R☉
Surface gravity (log g)	2.72[5] cgs
Temperature	4,760[5] K
Metallicity [Fe/H]	–0.36[5] dex
Other designations
Alnasl, Nushaba, Warida,[6] γ Sagittarii, γ Sgr, Gamma^2 Sgr, 10 Sagittarii, CPD-30  5241, FK5 679, GC 24632, HD 165135, HIP 88635, HR 6746, PPM 297231, SAO 209696,[7]
Database references
SIMBAD	data

Gamma² Sagittarii (Gamma² Sgr, γ² Sagittarii, γ² Sgr) is a 3rd-magnitude star in the zodiac constellation Sagittarius. The location of this star forms the tip of the arrow in the bow of Sagittarius the Centaur. It has the proper names Alnasl (Nasl, El Nasl), Nushaba (Nash) and Warida.^[6]

This star is close enough to the Earth that its distance can be determined using parallax, yielding a value of about 96.9 light-years (29.7 parsecs). It has an apparent visual magnitude of +2.98,^[2] making it the seventh brightest star in the constellation. A stellar classification of K1 III reveals that this is a giant star,^[2] having expanded to an estimated 12 times the Sun's radius.^[4] This means it has exhausted the hydrogen in its core and evolved away from the main sequence. The abundance of elements other than hydrogen and helium in this star, what astronomers term the star's metallicity,^[5] is lower than in the Sun. Gamma² Sagittarii has an effective temperature of 4,760 K,^[5] compared to 5,778 K for the Sun.^[8] It is this lower temperature that gives Gamma² Sagittarii the orange hue that is a characteristic of K-type stars.

There is a fainter optical companion Gamma¹ Sagittarii located about 50 arcminutes north of this star. It is magnitude 4.7 Cepheid variable star designated W Sagittarii.^[9][10]

Name and etymology

• Alnasl is derived from the Arabic النصل al-naşl meaning "arrowhead".,^[11] Nushaba is derived from the Arabic Zujj al-Nashshaba meaning the same as Alnasl.,^[12] Warida is derived from النعم الوارد Al Naʽām al Wārid, the Going Ostriches, the asterism consisting this star, δ Sgr, ε Sgr and η Sgr.^[12]
• This star, together with :
  • δ Sgr, ε Sgr, ζ Sgr, λ Sgr, σ Sgr, τ Sgr and φ Sgr, comprising the asterism Teapot.^[13][14]
  • δ Sgr and ε Sgr were Akkadian Sin-nun‑tu, or Si-nu-nu‑tum, the Swallow.^[12]
• In the catalogue of stars in the Calendarium of Al Achsasi al Mouakket, this star was designated Aoul al Waridah, which was translated into Latin as Prima τού al Warida, meaning first going ostrich.^[15]
• In Chinese, 箕 (Jī), meaning Winnowing Basket, refers to an asterism consisting of γ Sagittarii, δ Sagittarii, ε Sagittarii and η Sagittarii. Consequently, γ Sagittarii itself is known as 箕宿一 (Jī Sù yī, English: the First Star of Winnowing Basket.)^[16]

References

1. van Leeuwen, F. (November 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
2. Wielen, R.; et al. (1999), "Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions", Veröff. Astron. Rechen-Inst. Heidelb (Astronomisches Rechen-Institut Heidelberg) 35 (35): 1, Bibcode:1999VeARI..35....1W
3. 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
4. Pasinetti-Fracassini, L. E.; et al. (February 2001), "Catalogue of Stellar Diameters (CADARS)", Astronomy and Astrophysics 367 (2): 521–524, arXiv:astro-ph/0012289, Bibcode:2001A&A...367..521P, doi:10.1051/0004-6361:20000451
5. McWilliam, Andrew (December 1990), "High-resolution spectroscopic survey of 671 GK giants. I - Stellar atmosphere parameters and abundances", Astrophysical Journal Supplement Series 74: 1075–1128, Bibcode:1990ApJS...74.1075M, doi:10.1086/191527
6. Olcott, William Tyler (1907), A field book of the stars (2nd ed.), G. P. Putnam's sons, p. 136
7. "gam Sgr -- Variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg), retrieved 2012-01-05
8. "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, retrieved 2012-01-16
9. Kaler, James B., "ALNASL (Gamma-2 and Gamma-1=W Sagittarii)", Stars (University of Illinois), retrieved 2012-01-05
10. Burnham, Robert (1978), Burnham's celestial handbook: an observer's guide to the universe beyond the solar system, Dover books explaining science 3 (2nd ed.), Courier Dover Publications, p. 1560, ISBN 0-486-23673-0
11. Ridpath, Ian (1989), Star tales, James Clarke & Co., p. 113, ISBN 0-7188-2695-7
12. 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.
13. "Sagittarius". deepsky.astroinfo.org. Retrieved 30 August 2008.
14. skywatchers Archived May 17, 2007, at the Wayback Machine.
15. Knobel, E. B. (June 1895). "Al Achsasi Al Mouakket, on a catalogue of stars in the Calendarium of Mohammad Al Achsasi Al Mouakket". Monthly Notices of the Royal Astronomical Society 55: 435. Bibcode:1895MNRAS..55..429K. doi:10.1093/mnras/55.8.429.
16. (Chinese) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 11 日