Eta1 Hydri

Eta1 Hydri, Latinized from η1 Hydri, is a blue-white hued star in the southern constellation of Hydrus. It has an apparent visual magnitude of 6.76,[2] which may be too faint to be visible to the naked eye. Based upon an annual parallax shift of 5.27 mas as measured from Earth,[1] the system is located about 619 light years distant from the Sun. At that distance, the visual magnitude of the star is diminished by 0.10 magnitudes of extinction due to interstellar dust.[5] The star is drifting further away with a heliocentric radial velocity of +15 km/s.[2]

For other stars with this Bayer designation, see η Hydri.
Eta1 Hydri
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydrus
Right ascension 01h 52m 34.78591s[1]
Declination −67° 56′ 40.1823″[1]
Apparent magnitude (V) 6.76[2]
Characteristics
Spectral type B9 V[3]
B−V color index −0.050±0.002[4]
Astrometry
Radial velocity (Rv)+15.0±3.0[2] km/s
Proper motion (μ) RA: +18.270[1] mas/yr
Dec.: −8.948[1] mas/yr
Parallax (π)5.2719 ± 0.0548[1] mas
Distance619 ± 6 ly
(190 ± 2 pc)
Absolute magnitude (MV)+0.77[5]
Details
Luminosity91[6] L☉
Temperature9,816[6] K
Age311[5] Myr
Other designations
η1 Hyi, CD−68°87, HD 11733, HIP 8751, SAO 248455[7]
Database references
SIMBADdata

This is a B-type main-sequence star with a stellar classification of B9 V[3] that was suspected in 1939 by Herbert Schneller of being variable.[8] However, this may have been based on a photographic plate that was later rejected.[9] It is listed in the General Catalogue of Variable Stars, but marked as probably constant.[10]

The star is about 311[5] million years old and is radiating 91 times the luminosity of the Sun from its photosphere at an effective temperature of 9,816 K.[6]

References
  1. Brown, A. G. A.; et al. (Gaia collaboration) (August 2018). "Gaia Data Release 2: Summary of the contents and survey properties". Astronomy & Astrophysics. 616. A1. arXiv:1804.09365. Bibcode:2018A&A...616A...1G. doi:10.1051/0004-6361/201833051. Gaia DR2 record for this source at VizieR.
  2. de Bruijne, J. H. J.; Eilers, A.-C. (October 2012), "Radial velocities for the HIPPARCOS-Gaia Hundred-Thousand-Proper-Motion project", Astronomy & Astrophysics, 546: 14, arXiv:1208.3048, Bibcode:2012A&A...546A..61D, doi:10.1051/0004-6361/201219219, A61.
  3. Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.
  4. Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters, 38 (5): 331, arXiv:1108.4971, Bibcode:2012AstL...38..331A, doi:10.1134/S1063773712050015.
  5. Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters, 38 (11): 694–706, arXiv:1606.09028, Bibcode:2012AstL...38..694G, doi:10.1134/S1063773712110035.
  6. McDonald, I.; et al. (2012), "Fundamental Parameters and Infrared Excesses of Hipparcos Stars", Monthly Notices of the Royal Astronomical Society, 427 (1): 343–57, arXiv:1208.2037, Bibcode:2012MNRAS.427..343M, doi:10.1111/j.1365-2966.2012.21873.x.
  7. "eta1 Hyi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-08-18.
  8. "Eta1 Hydri", International Variable Star Index, AAVSO, January 4, 2010, retrieved 12 September 2013.
  9. Sahade, Jorge; Albarracín, Julio (March 1950), "Spectrographic Observations of the Star η1 Hydri", Astrophysical Journal, 111: 442, Bibcode:1950ApJ...111..442S, doi:10.1086/145283.
  10. Samus, N. N.; Durlevich, O. V.; et al. (2009), "VizieR Online Data Catalog: General Catalogue of Variable Stars (Samus+ 2007-2013)", VizieR On-line Data Catalog: B/GCVS. Originally Published in: 2009yCat....102025S, 1: B/gcvs, Bibcode:2009yCat....102025S.
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