Astronomy:Eta Orionis
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| Observation data Equinox J2000.0]] (ICRS) | |
|---|---|
| Constellation | Orion |
| Right ascension | 05h 24m 28.61672s[1] |
| Declination | –02° 23′ 49.7311″[1] |
| Apparent magnitude (V) | 3.42[2] (4.50 + 5.90 + 5.65 + 4.95)[3] |
| Characteristics | |
| Spectral type | Aa: B1 V Ab: B3 V Ac: B3 V B: B2 V[3] |
| U−B color index | –0.90[2] |
| B−V color index | −0.17[2] |
| Variable type | Algol[4] |
| Astrometry | |
| Radial velocity (Rv) | +19.8[5] km/s |
| Proper motion (μ) | RA: −0.71[1] mas/yr Dec.: −3.46[1] mas/yr |
| Parallax (π) | 3.34 ± 1.07[1] mas |
| Distance | approx. 1,000 ly (approx. 300 pc) |
| Orbit[6] | |
| Primary | Aa |
| Companion | Ab |
| Period (P) | 7.989255±0.000005 days |
| Eccentricity (e) | 0.011±0.0002 |
| Inclination (i) | 85° |
| Semi-amplitude (K1) (primary) | 145.5±0.03 km/s |
| Semi-amplitude (K2) (secondary) | 150±3 km/s |
| Orbit[3] | |
| Companion | Ac |
| Period (P) | 9.442±0.012 yr |
| Semi-major axis (a) | 0.0441±0.0015″ |
| Eccentricity (e) | 0.45±0.02 |
| Inclination (i) | 102.8±1.8° |
| Details | |
| η Ori Aa | |
| Mass | 11.0±0.5[6] M☉ |
| Radius | 6.3±0.6[6] R☉ |
| Temperature | 26,600[6] K |
| Rotational velocity (v sin i) | 20[6] km/s |
| η Ori Ab | |
| Mass | 10.6±0.7[6] M☉ |
| Radius | 5.2±0.4[6] R☉ |
| Temperature | 26,600[6] K |
| Rotational velocity (v sin i) | 130[6] km/s |
| η Ori Ac | |
| Mass | 6.78[7] M☉ |
| η Ori B | |
| Mass | 8.7[7] M☉ |
| Other designations | |
| Database references | |
| SIMBAD | data |
Eta Orionis, Latinized from η Orionis, is a multiple star in the constellation Orion. It lies a little to the west of Orion's Belt between Delta Orionis and Rigel, being closer to Delta Orionis than to Rigel. It lies at a distance of around 1,000 light-years from Earth and is part of the Orion OB1 association.
System
Eta Orionis is listed in multiple star catalogues as having two companions: a bright component B less than 2″ away; and a faint component C nearly 2′ away.[9] The two are estimated to orbit every 1,800 years.[7]
The primary star, Eta Orionis A, is itself a spectroscopic triple star, known from multiple spectral lines with varying radial velocities.[6] The most distant component Ac, has been resolved using speckle interferometry, at a separation of about 0.04″. It orbits the other two in 9.4 years.[3] The two closest stars, Aa and Ab, are separated by only about a tenth of an astronomical unit and orbit in just under eight days.[6]
The system lies within the Orion OB1 association, a group of massive stars that includes most of the bright stars of Orion.[10] It is assigned to the oldest and closest part of the association, known as OB1a.[11]
Variability
Eta Orionis drops in brightness every four days from a combined apparent magnitude of 3.31 to about magnitude 3.6. This is due to eclipses between the two closest components, Aa and Ab.[4] The primary and secondary eclipses are very similar, 0.24 and 0.23 magnitudes deep, respectively.[13]
It has also been suggested that component Ab is intrinsically variable with a period of 0.3 days and a very small amplitude. This star has unusual variable spectral lines and lies with the β Cephei variable instability strip.[6] However, it is now thought that the variable component is either B and Ac, possibly due to an unseen companion or rotational modulation. The actual period is 0.432 days and the 0.3-day period was an alias.[13]
See also
References
- ↑ 1.0 1.1 1.2 1.3 1.4 van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics 474 (2): 653–664. doi:10.1051/0004-6361:20078357. Bibcode: 2007A&A...474..653V.
- ↑ 2.0 2.1 2.2 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. doi:10.1086/111220. Bibcode: 1971AJ.....76.1058C.
- ↑ 3.0 3.1 3.2 3.3 Balega, I. I; Balega, Yu. Yu; Hofmann, K. -H; Tokovinin, A. A; Weigelt, G. P (1999). "Parameters of four multiple systems from speckle interferometry". Astronomy Letters 25 (12): 797. Bibcode: 1999AstL...25..797B.
- ↑ 4.0 4.1 Watson (2006–2012). "AAVSO International Variable Star Index VSX". http://vizier.u-strasbg.fr/viz-bin/VizieR-5?-ref=VIZ50b5568460a0&-out.add=.&-source=B/vsx/vsx&recno=21262.
- ↑ Evans, D. S. (June 20–24, 1966). "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and Their Applications, Proceedings from IAU Symposium No. 30 30: 57. Bibcode: 1967IAUS...30...57E.
- ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 De Mey, K.; Aerts, C.; Waelkens, C.; Van Winckel, H. (1996). "The early-type multiple system η Orionis. II. Line profile variations in component Ab". Astronomy and Astrophysics 310: 164. Bibcode: 1996A&A...310..164D.
- ↑ 7.0 7.1 7.2 "HIP 25281". http://www.ctio.noao.edu/~atokovin/stars/stars.php?cat=HIP&number=25281.
- ↑ "CCDM J05245-0223AB -- Double or multiple star". SIMBAD. Centre de Données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-id?Ident=Eta+Orionis.
- ↑ Mason, Brian D; Wycoff, Gary L; Hartkopf, William I; Douglass, Geoffrey G; Worley, Charles E (2001). "The 2001 US Naval Observatory Double Star CD-ROM. I. The Washington Double Star Catalog". The Astronomical Journal 122 (6): 3466. doi:10.1086/323920. Bibcode: 2001AJ....122.3466M.
- ↑ Abt, H. A; Levato, H (1977). "Spectral types in the Orion OB1 association". Publications of the Astronomical Society of the Pacific 89: 797. doi:10.1086/130230. Bibcode: 1977PASP...89..797A.
- ↑ Warren, W. H. Jr; Hesser, J. E (1978). "A photometric study of the Orion OB 1 association. III - Subgroup analyses". The Astrophysical Journal Supplement Series 36: 497. doi:10.1086/190510. Bibcode: 1978ApJS...36..497W.
- ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html.
- ↑ 13.0 13.1 Waelkens, C.; Lampens, P. (1988). "The early-type multiple system eta Orionis. I. Photometric variability and rediscussion of the physical parameters of the components". Astronomy and Astrophysics 194: 143. Bibcode: 1988A&A...194..143W.
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