Eta1 Hydri

Eta¹ Hydri
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Hydrus
Right ascension	01h 52m 34.78591s
Declination	−67° 56′ 40.1823″
Apparent magnitude (V)	6.76
Characteristics
Evolutionary stage	main sequence
Spectral type	B9 V
B−V color index	−0.050±0.002
Astrometry
Radial velocity (Rv)	+15.0±3.0 km/s
Proper motion (μ)	RA: +18.270 mas/yr ; Dec.: −8.948 mas/yr
Parallax (π)	5.2719±0.0548 mas
Distance	619 ± 6 ly ; (190 ± 2 pc)
Absolute magnitude (MV)	+0.77
Details
Mass	2.7 M☉
Radius	2.8 R☉
Luminosity	83 L☉
Surface gravity (log g)	3.98 cgs
Temperature	10,445 K
Age	311 Myr
Other designations
	η1 Hyi, AAVSO 0152-68, CD−68°87, HD 11733, HIP 8751, SAO 248455
Database references
SIMBAD	data

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.^[6] The star is drifting further away with a heliocentric radial velocity of +15 km/s.^[2]

This is a B-type main-sequence star with a stellar classification of B9 V^[4] that was suspected in 1939 by Herbert Schneller of being variable.^[9] However, this may have been based on a photographic plate that was later rejected.^[10] It is listed in the General Catalogue of Variable Stars, but marked as probably constant.^[11]

The star is about 311^[6] million years old^[6] and is radiating 83 times the luminosity of the Sun from its photosphere at an effective temperature of 10,445 K.^[7]

References

^ ^a ^b ^c ^d ^e ^f 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.
^ ^a ^b ^c ^d 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, S2CID 59451347, A61.
^ Ijspeert, L. W.; Tkachenko, A.; Johnston, C.; Garcia, S.; De Ridder, J.; Van Reeth, T.; Aerts, C. (2021). "An all-sky sample of intermediate- to high-mass OBA-type eclipsing binaries observed by TESS". Astronomy and Astrophysics. 652: A120. arXiv:2107.10005. Bibcode:2021A&A...652A.120I. doi:10.1051/0004-6361/202141489.
^ ^a ^b Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.
^ 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, S2CID 119257644.
^ ^a ^b ^c ^d ^e 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, S2CID 119108982.
^ ^a ^b ^c ^d ^e ^f Stassun, Keivan G.; et al. (2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467.
^ "eta1 Hyi", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-08-18.
^ "Eta1 Hydri", International Variable Star Index, AAVSO, January 4, 2010, retrieved 12 September 2013.
^ 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.
^ 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.

[GaiaDR2-1] ^ ^a ^b ^c ^d ^e ^f 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.

[deBruijne2012-2] 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, S2CID 59451347, A61.

[ijspeert2021-3] Ijspeert, L. W.; Tkachenko, A.; Johnston, C.; Garcia, S.; De Ridder, J.; Van Reeth, T.; Aerts, C. (2021). "An all-sky sample of intermediate- to high-mass OBA-type eclipsing binaries observed by TESS". Astronomy and Astrophysics. 652: A120. arXiv:2107.10005. Bibcode:2021A&A...652A.120I. doi:10.1051/0004-6361/202141489.

[houk1979-4] Houk, Nancy (1979), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1978mcts.book.....H.

[Anderson2012-5] 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, S2CID 119257644.

[Gontcharov2012-6] 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, S2CID 119108982.

[tic-7] ^ ^a ^b ^c ^d ^e ^f Stassun, Keivan G.; et al. (2019). "The Revised TESS Input Catalog and Candidate Target List". The Astronomical Journal. 158 (4): 138. arXiv:1905.10694. Bibcode:2019AJ....158..138S. doi:10.3847/1538-3881/ab3467.

[SIMBAD-8] "eta1 Hyi", SIMBAD, Centre de données astronomiques de Strasbourg, retrieved 2017-08-18.

[AAVSO-9] "Eta1 Hydri", International Variable Star Index, AAVSO, January 4, 2010, retrieved 12 September 2013.

[Sahade1950-10] 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.

[gcvs-11] 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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Observation data Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Hydrus
Right ascension	01^h 52^m 34.78591^s^[1]
Declination	−67° 56′ 40.1823″^[1]
Apparent magnitude (V)	6.76^[2]
Characteristics
Evolutionary stage	main sequence^[3]
Spectral type	B9 V^[4]
B−V color index	−0.050±0.002^[5]
Astrometry

Radial velocity (R_v)	+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 mas^[1]
Distance	619 ± 6 ly (190 ± 2 pc)
Absolute magnitude (M_V)	+0.77^[6]

Details

Mass	2.7^[7] `M`_☉
Radius	2.8^[7] `R`_☉
Luminosity	83^[7] `L`_☉
Surface gravity (log g)	3.98^[7] cgs
Temperature	10,445^[7] K
Age	311^[6] Myr

Other designations
η¹ Hyi, AAVSO 0152-68, CD−68°87, HD 11733, HIP 8751, SAO 248455^[8]
Database references
SIMBAD	data

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