| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Orion |
| Pronunciation | /ælˈnaɪtæk/,[1] |
| Right ascension | 05h 40m 45.52666s[2] |
| Declination | −01° 56′ 34.2649″[2] |
| Apparent magnitude (V) | 1.77[3] (2.08 + 4.28 + 4.01[4]) |
| Characteristics | |
| Evolutionary stage | Blue supergiant (Aa) |
| Spectral type | O9.5Iab + B1IV + B0III[4] |
| U−B color index | −1.06[3] |
| B−V color index | −0.11 (A) −0.20 (B)[5] |
| Astrometry | |
| Radial velocity (Rv) | 18.50[6] km/s |
| Proper motion (μ) | RA: 3.19[2] mas/yr Dec.: 2.03[2] mas/yr |
| Parallax (π) | 4.43 ± 0.64 mas[2] |
| Distance | 1,260 ± 180 ly (387 ± 54[4] pc) |
| Absolute magnitude (MV) | −6.0 / −3.9 / −4.1[4] |
| Orbit[4] | |
| Primary | Aa |
| Companion | Ab |
| Period (P) | 2,687.3±7.0 d |
| Semi-major axis (a) | 35.9±0.2 mas |
| Eccentricity (e) | 0.338±0.004 |
| Inclination (i) | 139.3±0.6° |
| Longitude of the node (Ω) | 83.8±0.8° |
| Periastron epoch (T) | JD 2452734.2±9.0 |
| Argument of periastron (ω) (secondary) | 204.2±1.2° |
| Semi-amplitude (K1) (primary) | 10.1 km/s |
| Semi-amplitude (K2) (secondary) | 19.6 km/s |
| Orbit[7] | |
| Primary | A |
| Companion | B |
| Period (P) | 1,508.6 yr |
| Semi-major axis (a) | 2.728″ |
| Eccentricity (e) | 0.07 |
| Inclination (i) | 72.0° |
| Longitude of the node (Ω) | 155.5° |
| Periastron epoch (T) | 2,070.6 |
| Argument of periastron (ω) (secondary) | 47.3° |
| Details | |
| Alnitak Aa | |
| Mass | 33±10[4] M☉ |
| Radius | 20.0±3.2[4] R☉ |
| Luminosity | 250,000[4] L☉ |
| Surface gravity (log g) | 3.2±0.1[8] cgs |
| Temperature | 29,500±1,000[4] K |
| Rotation | 6.67 days[9] |
| Rotational velocity (v sin i) | 110±10[4] km/s |
| Age | 6.4[4] Myr |
| Alnitak Ab | |
| Mass | 14±3[4] M☉ |
| Radius | 7.3±1.0[4] R☉ |
| Luminosity | 32,000[4] L☉ |
| Temperature | 29,000[10] K |
| Age | 7.2[4] Myr |
| Alnitak B | |
| Rotational velocity (v sin i) | 350[4] km/s |
| Age | ~7[4] Myr |
| Other designations | |
| A: HD 37742, HR 1948 | |
| B: HD 37743, HR 1949 | |
| Database references | |
| SIMBAD | AB |
| A | |
| B | |
Alnitak is a triple star system in the constellation of Orion. It has the designations ζ Orionis, which is Latinised to Zeta Orionis and abbreviated Zeta Ori or ζ Ori, and 50 Orionis, abbreviated 50 Ori. The system is located at a distance of several hundred parsecs from the Sun and is one of the three main stars of Orion's Belt along with Alnilam and Mintaka.
The primary star, Alnitak Aa, is a hot blue supergiant with an absolute magnitude of −6.0 and is the brightest class O star in the night sky with a visual magnitude of +2.0. It has two companions—Ab and B, the latter known for the longest time and the former discovered recently, producing a combined magnitude for the trio of +1.77. The stars are members of the Orion OB1 association and the Collinder 70 [de] association.
- ^ Kunitzsch, Paul; Smart, Tim (2006). A Dictionary of Modern star Names: A Short Guide to 254 Star Names and Their Derivations (2nd rev. ed.). Cambridge, Massachusetts: Sky Pub. ISBN 978-1-931559-44-7.
- ^ a b c d e Van Leeuwen, F. (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. S2CID 18759600.
- ^ a b Ducati, J. R. (2002). "VizieR Online Data Catalog: Catalogue of Stellar Photometry in Johnson's 11-color system". CDS/ADC Collection of Electronic Catalogues. 2237: 0. Bibcode:2002yCat.2237....0D.
- ^ a b c d e f g h i j k l m n o p q Hummel, C. A.; Rivinius, T.; Nieva, M. -F.; Stahl, O.; Van Belle, G.; Zavala, R. T. (2013). "Dynamical mass of the O-type supergiant in ζ Orionis A". Astronomy & Astrophysics. 554: A52. arXiv:1306.0330. Bibcode:2013A&A...554A..52H. doi:10.1051/0004-6361/201321434. S2CID 53645495.
- ^ Fabricius, C.; Høg, E.; Makarov, V. V.; Mason, B. D.; Wycoff, G. L.; Urban, S. E. (2002). "The Tycho double star catalogue". Astronomy and Astrophysics. 384 (1): 180–189. Bibcode:2002A&A...384..180F. doi:10.1051/0004-6361:20011822. ISSN 0004-6361.
- ^ Kharchenko, N.V.; Scholz, R.-D.; Piskunov, A.E.; Röser, S.; Schilbach, E. (2007). "Astrophysical supplements to the ASCC-2.5: Ia. Radial velocities of ~55000 stars and mean radial velocities of 516 Galactic open clusters and associations". Astronomische Nachrichten. 328 (9): 889–896. arXiv:0705.0878. Bibcode:2007AN....328..889K. doi:10.1002/asna.200710776. ISSN 0004-6337. S2CID 119323941.
- ^ "Sixth Catalog of Orbits of Visual Binary Stars". United States Naval Observatory.
- ^ Raassen, A. J. J.; Van Der Hucht, K. A.; Miller, N. A.; Cassinelli, J. P. (2008). "XMM-Newton observations of ζ Orionis (O9.7 Ib): A collisional ionization equilibrium model". Astronomy and Astrophysics. 478 (2): 513. arXiv:0803.0873. Bibcode:2008A&A...478..513R. doi:10.1051/0004-6361:20077891. S2CID 17601299.
- ^ Buysschaert, B.; Neiner, C.; Ramiaramanantsoa, T.; Richardson, N. D.; David-Uraz, A.; Moffat, A. F. J. (2016). "Understanding the photometric variability of ζ OriAa". Second Brite-Constellation Science Conference: Small Satellites – Big Science. 5: 101. arXiv:1610.05625. Bibcode:2017sbcs.conf..101B.
- ^ Blazère, A.; Neiner, C.; Tkachenko, A.; Bouret, J.-C.; Rivinius, Th. (2015). "The magnetic field of ζ Orionis A". Astronomy & Astrophysics. 582: A110. arXiv:1509.02773. Bibcode:2015A&A...582A.110B. doi:10.1051/0004-6361/201526855. S2CID 62800990.