Gamma Sagittarii
 Location of γ Sagittarii (circled) |
|
| Observation data Epoch J2000.0 Equinox J2000.0 |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 18h 05m 48.48810s[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] |
| Temperature | 4,760[5] K |
| Metallicity [Fe/H] | –0.36[5] dex |
| Other designations | |
| Database references | |
| SIMBAD | data |
Gamma Sagittarii (γ Sagittarii, γ 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] Alnasl is derived from the Arabic النصل al-naşl meaning "arrowhead".[8] Nushaba is derived from the Arabic Zujj al-Nashshaba meaning the same as Alnasl.[9]
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. Gamma Sagittarii has an effective temperature of 4,760 K,[5] compared to 5,778 K for the Sun.[10] It is this lower temperature that gives Gamma Sagittarii the orange hue that is a characteristic of K-type stars.
There is a fainter optical companion located about 50 arcminutes north of this star. It is magnitude 4.7 Cepheid variable star designated W Sagittarii.[11][12]
[edit] References
- ^ a b c d e van Leeuwen, F. (November 2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics 474 (2): 653–664, Bibcode 2007A&A...474..653V, doi:10.1051/0004-6361:20078357
- ^ a b c d e Wielen, R. et al. (1999), Sixth Catalogue of Fundamental Stars (FK6). Part I. Basic fundamental stars with direct solutions, Astronomisches Rechen-Institut Heidelberg, Bibcode 1999VeARI..35....1W
- ^ a b Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99), Bibcode 1966CoLPL...4...99J
- ^ a b Pasinetti-Fracassini, L. E. et al. (February 2001), "Catalogue of Stellar Diameters (CADARS)", Astronomy and Astrophysics 367: 521–524, Bibcode 2001A&A...367..521P, doi:10.1051/0004-6361:20000451
- ^ a b c d e 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
- ^ a b Olcott, William Tyler (1907), A field book of the stars (2nd ed.), G. P. Putnam's sons, p. 136, http://books.google.com/books?id=47IAAAAAMAAJ&pg=PA136
- ^ "gam Sgr -- Variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Gamma+Sagittarii, retrieved 2012-01-05
- ^ Ridpath, Ian (1989), Star tales, James Clarke & Co., p. 113, ISBN 0718826957, http://books.google.com/books?id=gFrdcTdeVaEC&pg=RA1-PA13
- ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 357, http://books.google.com/books?id=5xQuAAAAIAAJ&pg=PA357
- ^ "The Colour of Stars", Australia Telescope, Outreach and Education (Commonwealth Scientific and Industrial Research Organisation), December 21, 2004, http://outreach.atnf.csiro.au/education/senior/astrophysics/photometry_colour.html, retrieved 2012-01-16
- ^ Kaler, James B., "ALNASL (Gamma-2 and Gamma-1=W Sagittarii)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/alnasl.html, retrieved 2012-01-05
- ^ 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 0486236730, http://books.google.com/books?id=PJzIt3SIlkUC&pg=PA1560
