Alpha Sagittarii
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Sagittarius |
| Right ascension | 19h 23m 53.1765s[1] |
| Declination | −40° 36′ 57.384″[1] |
| Apparent magnitude (V) | +3.97[2] |
| Characteristics | |
| Spectral type | B8V[3] |
| U−B color index | −0.33[2] |
| B−V color index | −0.10[2] |
| Astrometry | |
| Radial velocity (Rv) | −0.7[4] km/s |
| Proper motion (μ) | RA: 32.67[1] mas/yr Dec.: −120.81[1] mas/yr |
| Parallax (π) | 19.20 ± 0.99[1] mas |
| Distance | 170 ± 9 ly (52 ± 3 pc) |
| Details | |
| Radius | 2.49 R☉ |
| Luminosity | 60 L☉ |
| Temperature | 12,370 ± 500[5] K |
| Metallicity | ![\begin{smallmatrix}\left[\frac{Fe}{H} \right]\ =\ -0.02\end{smallmatrix}](/2012-wikipedia_en_all_nopic_01_2012/I/02e4908db78403c89b20b0107a902b3a.png) [6] |
| Other designations | |
Alpha Sagittarii (α Sgr, α Sagittarii) is a star in the Sagittarius constellation. It has the traditional names 天淵三 , Alrami and Rukbat, derived from the Arabic rukbat al-rāmī = the knee of the archer. It is not to be confused with Delta Cassiopeiae, which also is called Ruchbah or Rukbat, from the Arabic word ركبة rukbah meaning "knee".
Alpha Sagittarii is a blue, class B dwarf star. It does not appear particularly bright in the sky to the naked eye, with a visual apparent magnitude of +3.97. However, this is due to its distance; in reality, the star is twice as hot as the Sun and considerably more massive, with a luminosity in visible wavelengths about 40 times greater than that of the Sun. Based on an excess emission of infrared radiation, it may have a debris disk, much like Vega.[6]
This is a single-lined spectroscopic binary system. The ROSAT All Sky Survey discovered that Alpha Sagittarii is emitting an excess flux of X-rays, which is not expected to originate from a star of this spectral class. The most likely explanation is that the companion is an active pre-main sequence star or else a star that has just reached the main sequence.[8]
See also
References
- ^ a b c d e Perryman, M. A. C. et al. (1997), "The Hipparcos Catalogue", Astronomy & Astrophysics 323: L49–L52, Bibcode 1997A&A...323L..49P
- ^ a b c 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.
- ^ Buscombe, W. (1962). "Spectral classification of Southern fundamental stars". Mount Stromlo Observatory Mimeogram 4. Bibcode 1962MtSOM...4....1B.
- ^ Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". In Batten, Alan Henry; Heard, John Frederick. Determination of Radial Velocities and their Applications, Proceedings from IAU Symposium no. 30. University of Toronto: International Astronomical Union. http://adsabs.harvard.edu/abs/1967IAUS...30...57E. Retrieved 2009-09-10.
- ^ Sokolov, N. A. (May 1995). "The determination of T_eff_ of B, A and F main sequence stars from the continuum between 3200 A and 3600 A". Astronomy and Astrophysics Supplement 110: 553−564. Bibcode 1995A&AS..110..553S.
- ^ a b Saffe, C.; et al. (October 2008). "Spectroscopic metallicities of Vega-like stars". Astronomy and Astrophysics 490 (1): 297−305. Bibcode 2008A&A...490..297S. doi:10.1051/0004-6361:200810260.
- ^ "RUKBAT". SIMBAD. Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=RUKBAT. Retrieved 2009-10-01.
- ^ Hubrig, S.; et al. (June 2001). "Search for low-mass PMS companions around X-ray selected late B stars". Astronomy and Astrophysics 372: 152−164. arXiv:astro-ph/0103201. Bibcode 2001A&A...372..152H. doi:10.1051/0004-6361:20010452.
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