Eta Orionis

η Orionis
Location of η Orionis (circled)
Observation data
Epoch J2000      Equinox J2000
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
Distanceapprox. 1,000 ly
(approx. 300 pc)
Orbit[6]
PrimaryAa
CompanionAb
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]
CompanionAc
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°
Orbit[7]
PrimaryA
CompanionB
Period (P)704.8±127.7 yr
Semi-major axis (a)0.970±0.331″
Eccentricity (e)0.914±0.165
Inclination (i)96.9±13.8°
Details
η Ori Aa
Mass11.0±0.5[6] M☉
Radius6.3±0.6[6] R☉
Temperature26,600[6] K
Rotational velocity (v sin i)20[6] km/s
η Ori Ab
Mass10.6±0.7[6] M☉
Radius5.2±0.4[6] R☉
Temperature26,600[6] K
Rotational velocity (v sin i)130[6] km/s
Other designations
η Ori, 28 Orionis, BD−02°1235, HD 35411, HIP 25281, HR 1788, SAO 132071.[8]
Database references
SIMBADdata

Eta Orionis (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.

Nomenclature

The proper name Saiph is Arabic for "sword",[9] and Algjebbah Arabic for "scutum".[10]

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.[11]

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.[12] It is assigned to the oldest and closest part of the association, known as OB1a.[13]

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.[14]

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.[14]

See also

References

  1. 1 2 3 4 5 van Leeuwen, F. (2007), "Validation of the new Hipparcos reduction", Astronomy and Astrophysics, 474 (2): 653–664, arXiv:0708.1752 [astro-ph], Bibcode:2007A&A...474..653V, doi:10.1051/0004-6361:20078357 Cite uses deprecated parameter |class= (help)
  2. 1 2 3 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.
  3. 1 2 3 4 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. 1 2 AAVSO International Variable Star Index VSX (Watson+, 2006-2012) VizieR
  5. ↑ Evans, D. S. (June 20–24, 1966). Batten, Alan Henry; Heard, John Frederick, eds. "The Revision of the General Catalogue of Radial Velocities". Determination of Radial Velocities and Their Applications. 30: 57. Bibcode:1967IAUS...30...57E.
  6. 1 2 3 4 5 6 7 8 9 10 11 12 . Bibcode:1996A&A...310..164D. Missing or empty |title= (help)
  7. ↑ Zasche, P.; et al. (August 2009), "A Catalog of Visual Double and Multiple Stars With Eclipsing Components", The Astronomical Journal, 138 (2): 664–679, arXiv:0907.5172 [astro-ph.SR], Bibcode:2009AJ....138..664Z, doi:10.1088/0004-6256/138/2/664 Cite uses deprecated parameter |class= (help)
  8. ↑ "CCDM J05245-0223AB -- Double or multiple star", SIMBAD, Centre de Données astronomiques de Strasbourg, retrieved 2012-02-09
  9. ↑ Allen, R. H. (1899). Star-Names and Their Meanings. New York: G. E. Stechert. p. 316.
    Saiph was also used to indicate Kappa Orionis in the same constellation.
  10. ↑ Moore, P. (1983). The Guinness Book of Astronomy: Facts and Feats (2nd ed.). Middlesex: Guinness Superlatives Limited. p. 230.
  11. ↑ 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. Bibcode:2001AJ....122.3466M.
  12. ↑ Abt, H. A; Levato, H (1977). "Spectral types in the Orion OB1 association". Publications of the Astronomical Society of the Pacific. 89: 797. Bibcode:1977PASP...89..797A.
  13. ↑ 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.
  14. 1 2 . Bibcode:1988A&A...194..143W. Missing or empty |title= (help)
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