Kappa Orionis
 Location of κ Orionis (circled) |
|
| Observation data Epoch J2000 Equinox J2000 |
|
|---|---|
| Constellation | Orion |
| Right ascension | 05h 47m 45.38884s[1] |
| Declination | 09° 40′ 10.5777″[1] |
| Apparent magnitude (V) | 2.09[2] |
| Characteristics | |
| Spectral type | B0.5 Iab:[3] |
| U−B color index | –1.02[2] |
| B−V color index | –0.18[2] |
| Variable type | Slightly[4] |
| Astrometry | |
| Radial velocity (Rv) | +20.5[5] km/s |
| Proper motion (μ) | RA: +1.46[1] mas/yr Dec.: –1.28[1] mas/yr |
| Parallax (π) | 5.04 ± 0.22[1] mas |
| Distance | 650 ± 30 ly (198 ± 9 pc) |
| Absolute magnitude (MV) | –6.1[6] |
| Details | |
| Mass | 15.50 ± 1.25[7] M☉ |
| Radius | 22.2[6] R☉ |
| Luminosity | 56,881[7] L☉ |
| Surface gravity (log g) | 2.9[6] |
| Temperature | 26,500[6] K |
| Rotational velocity (v sin i) | 83[6] km/s |
| Age | 11.1 ± 0.5[8] Myr |
| Other designations | |
Kappa Orionis (κ Ori, κ Orionis, 53 Orionis) is the sixth-brightest star in the constellation of Orion. It has the traditional name Saiph.[9] Of the four bright stars that compose Orion's main quadrangle, it is the star at the south-eastern corner. A northern-hemisphere observer facing south would see it at the lower left of Orion, and a southern-hemisphere observer facing north would see it at the upper right. The name Saiph is from the Arabic saif al jabbar, literally sword of the giant.[10]
With an apparent visual magnitude of 2.1,[2] Kappa Orionis is the sixth brightest star in Orion. Parallax measurements yield an estimated distance of 650 light-years (198 parsecs) from Earth, which is about the same as Rigel.[1] It has a lower visual magnitude than Rigel because, although it is a much hotter star with a surface temperature of 26,500 K,[6] it emits most of its energy in the ultraviolet region of the spectrum, invisible to the human eye, paradoxically making it appear relatively dimmer.[10] The luminosity of this star changes slightly, varying by 0.04 magnitudes.[4]
Compared to the Sun this is an enormous star, with 14–17 times the mass and over 22 times the radius. It has a stellar classification of B0.5 Iab:.[3] The luminosity class 'Iab' represents a supergiant star that has exhausted the supply of hydrogen at its core and evolved away from the main sequence. However, the ':' indicates some uncertainty in the spectral value. Saiph has a strong stellar wind and is losing mass at the rate of 9.0 × 10–7 times the mass of the Sun per year, or the equivalent of the Sun's mass every 1.1 million years.[6] Large stars such as Saiph (and many other stars in Orion) are destined to collapse on themselves and explode as Type II supernovae.[10]
[edit] References
- ^ a b c d e f 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 Crawford, D. L.; Barnes, J. V.; Golson, J. C. (1971), "Four-color, H-beta, and UBV photometry for bright B-type stars in the northern hemisphere", The Astronomical Journal 76: 1058, Bibcode 1971AJ.....76.1058C, doi:10.1086/111220
- ^ a b c "SAIPH -- Variable Star", SIMBAD (Centre de Données astronomiques de Strasbourg), http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Kappa+Orionis, retrieved 2012-01-12
- ^ a b Lefèvre, L. et al. (November 2009), "A systematic study of variability among OB-stars based on HIPPARCOS photometry", Astronomy and Astrophysics 507 (2): 11411201, Bibcode 2009A&A...507.1141L, doi:10.1051/0004-6361/200912304
- ^ 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 c d e f g Crowther, P. A.; Lennon, D. J.; Walborn, N. R. (January 2006), "Physical parameters and wind properties of galactic early B supergiants", Astronomy and Astrophysics 446 (1): 279–293, arXiv:astro-ph/0509436, Bibcode 2006A&A...446..279C, doi:10.1051/0004-6361:20053685
- ^ a b Hohle, M. M.; Neuhäuser, R.; Schutz, B. F. (April 2010), "Masses and luminosities of O- and B-type stars and red supergiants", Astronomische Nachrichten 331 (4): 349, Bibcode 2010AN....331..349H, doi:10.1002/asna.200911355
- ^ Tetzlaff, N.; Neuhäuser, R.; Hohle, M. M. (January 2011), "A catalogue of young runaway Hipparcos stars within 3 kpc from the Sun", Monthly Notices of the Royal Astronomical Society 410 (1): 190–200, Bibcode 2011MNRAS.410..190T, doi:10.1111/j.1365-2966.2010.17434.x
- ^ Allen, Richard Hinckley (1899), Star-names and their meanings, G. E. Stechert, p. 317, http://books.google.com/books?id=5xQuAAAAIAAJ&pg=PA317
- ^ a b c Kaler, James B., "SAIPH (Kappa Orionis)", Stars (University of Illinois), http://stars.astro.illinois.edu/sow/saiph.html, retrieved 2012-01-27
