Astronomy:Eta Orionis

From HandWiki
Short description: Star in the constellation Orion
η Orionis
Location of η Orionis (circled)
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
Distanceapprox. 1,000 ly
(approx. 300 pc)
Orbit
PrimaryAa
CompanionAb
Period (P)7.98763(22)[6] days
Eccentricity (e)0.0095±0.0010[6]
Inclination (i)87.62±0.42[6]°
Argument of periapsis (ω)
(primary)		164±18[6]°
Semi-amplitude (K1)
(primary)		145.5±0.03[7] km/s
Semi-amplitude (K2)
(secondary)		150±3[7] 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°
Details
η Ori Aa
Mass10.87±0.44[6] M☉
Radius6.477±0.073[6] R☉
Surface gravity (log g)3.851±0.010[6] cgs
Temperature26,600[7] K
Rotational velocity (v sin i)20[7] km/s
η Ori Ab
Mass10.54±0.22[6] M☉
Radius4.79±0.10[6] R☉
Surface gravity (log g)4.100±0.016[6] cgs
Temperature25,950[6] K
Rotational velocity (v sin i)130[7] km/s
η Ori Ac
Mass6.78[8] M☉
η Ori B
Mass8.7[8] M☉
Other designations
η Ori, 28 Orionis, BD−02°1235, HD 35411, HIP 25281, HR 1788, SAO 132071[9]
Database references
SIMBADdata

Eta 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

Eta Orionis, Latinized from η Orionis, is the star's Bayer designation. It has the traditional Arabic name Saif al Jabbar, the Sword of the Giant, but this name is now used for another star, Saiph (Kappa Orionis).[10] It has also sometimes been called by the Latin name Ensis,[10] and Algjebbah.[11]

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.[12] The two are estimated to orbit every 1,800 years.[8]

The primary star, Eta Orionis A, is itself a spectroscopic triple star, known from multiple spectral lines with varying radial velocities.[7] 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.[7]

The system lies within the Orion OB1 association, a group of massive stars that includes most of the bright stars of Orion.[13] It is assigned to the oldest and closest part of the association, known as OB1a.[14]

Variability

A light curve for Eta Orionis, plotted from TESS data,[15] showing both eclipses and the 0.432 day 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.[16]

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.[7] 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.[16]

See also

References

  1. ↑ 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. ↑ 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. ↑ 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. ↑ 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. 
  5. ↑ 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. ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 Southworth, John; Bowman, Dominic M. (July 2022). "High-mass pulsators in eclipsing binaries observed using TESS". Monthly Notices of the Royal Astronomical Society 513 (3): 3191–3209. doi:10.1093/mnras/stac875. Bibcode: 2022MNRAS.513.3191S. 
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 7.7 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. 
  8. ↑ 8.0 8.1 8.2 "HIP 25281". http://www.ctio.noao.edu/~atokovin/stars/stars.php?cat=HIP&number=25281. 
  9. ↑ "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. 
  10. ↑ 10.0 10.1 Allen, R.H. (1899), Star Names: Their Lore and Meaning, p. 316, https://penelope.uchicago.edu/Thayer/E/Gazetteer/Topics/astronomy/_Texts/secondary/ALLSTA/Orion*.html 
  11. ↑ Darling, David. "Orion (constellation)". https://www.daviddarling.info/encyclopedia/O/Ori.html. 
  12. ↑ 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. 
  13. ↑ 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. 
  14. ↑ 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. 
  15. ↑ "MAST: Barbara A. Mikulski Archive for Space Telescopes". Space Telescope Science Institute. https://mast.stsci.edu/portal/Mashup/Clients/Mast/Portal.html. 
  16. ↑ 16.0 16.1 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. 



Retrieved from "https://handwiki.org/wiki/index.php?title=Astronomy:Eta_Orionis&oldid=3947599"