Theta Hydri

Theta Hydri
Observation data; Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Hydrus
Right ascension	03h 02m 15.449s
Declination	−71° 54′ 08.84″
Apparent magnitude (V)	5.53
Characteristics
Spectral type	B8 III/IV
U−B color index	−0.51
B−V color index	−0.14
Astrometry
Radial velocity (Rv)	+12.3±1.6 km/s
Proper motion (μ)	RA: +27.256 mas/yr ; Dec.: +16.598 mas/yr
Parallax (π)	6.4996±0.0619 mas
Distance	502 ± 5 ly ; (154 ± 1 pc)
Absolute magnitude (MV)	−0.48
Details
Luminosity	287 L☉
Surface gravity (log g)	3.76 cgs
Temperature	13,350 K
Rotation	4.3720 d
Age	211 Myr
Other designations
	θ Hyi, CPD−72°219, FK5 113, HD 19400, HIP 14131, HR 939, SAO 255945, WDS J03023-7154AB
Database references
SIMBAD	data

Theta Hydri, Latinized from θ Hydri, is a blue-white hued star in the southern constellation of Hydrus. It is faintly visible to the naked eye with an apparent visual magnitude of +5.53.^[2] Based upon an annual parallax shift of 6.50 mas as seen from Earth,^[1] it is located approximately 502 light years. At that distance, the visual magnitude of the star is diminished by an extinction of 0.10 due to interstellar dust.^[8] It is moving away from the Sun with a radial velocity of +12.3 km/s.^[4]

A stellar classification of B8 III/IV^[3] suggests it is an evolving B-type star showing mixed traits of a subgiant or giant star. It is a PGa star – a sub-class of the higher temperature chemically peculiar stars known as mercury-manganese stars (HgMn stars). That is, it displays a rich spectra of singly-ionized phosphorus and gallium, in addition to ionized mercury and manganese. As such, Theta Hydri forms a typical example of this type. The absorption lines for these ionized elements are found to vary, most likely as the result of uneven surface distribution combined with the star's rotation.^[10] It is a helium-weak star, having helium lines that are anomalously weak for its spectral type.^[6] A weak and variable longitudinal magnetic field has been detected.^[10]

There is a nearby companion star of class A0 IV^[11] located at an angular separation of 0.1 arc seconds along a position angle of 179°, as of 2002. Schöller et al. (2010) consider this to be a visual companion,^[12] although Eggleton and Tokovinin (2008) listed the pair as a probable binary star system.^[11]

References

^ ^a ^b ^c ^d ^e Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.
^ ^a ^b ^c ^d Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.
^ ^a ^b Houk, N.; Cowley, A. P. (1975), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1975mcts.book.....H.
^ ^a ^b 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.
^ ^a ^b 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 255204555.
^ ^a ^b ^c Alonso, M. S.; et al. (April 2003), "Elemental abundance studies of CP stars. The helium-weak stars HD 19400, HD 34797 and HD 35456*", Astronomy and Astrophysics, 402: 331−334, Bibcode:2003A&A...402..331A, doi:10.1051/0004-6361:20030222.
^ Barraza, L. F.; et al. (2022). "Rotation Signature of TESS B-type Stars. A Comprehensive Analysis". The Astrophysical Journal. 924 (2): 117. arXiv:2202.01022. Bibcode:2022ApJ...924..117B. doi:10.3847/1538-4357/ac3335. S2CID 246030494.
^ ^a ^b 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 255202762.
^ "tet Hyi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-10-13.{{cite web}}: CS1 maint: postscript (link)
^ ^a ^b Hubrig, S.; et al. (August 2014), "Abundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD 19400", Monthly Notices of the Royal Astronomical Society, 442 (4): 3604−3615, arXiv:1406.1927, Bibcode:2014MNRAS.442.3604H, doi:10.1093/mnras/stu1122.
^ ^a ^b Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.
^ Schöller, M.; et al. (November 2010), "Multiplicity of late-type B stars with HgMn peculiarity", Astronomy and Astrophysics, 522: 12, arXiv:1010.3643, Bibcode:2010A&A...522A..85S, doi:10.1051/0004-6361/201014246, S2CID 119273467, A85

[GaiaEDR3-1] Brown, A. G. A.; et al. (Gaia collaboration) (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics. 649: A1. arXiv:2012.01533. Bibcode:2021A&A...649A...1G. doi:10.1051/0004-6361/202039657. S2CID 227254300. (Erratum: doi:10.1051/0004-6361/202039657e). Gaia EDR3 record for this source at VizieR.

[Johnson1966-2] Johnson, H. L.; et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory, 4 (99): 99, Bibcode:1966CoLPL...4...99J.

[houk1975-3] Houk, N.; Cowley, A. P. (1975), Michigan catalogue of two-dimensional spectral types for the HD stars, vol. 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode:1975mcts.book.....H.

[deBruijne2012-4] 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.

[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 255204555.

[Alonso2003-6] Alonso, M. S.; et al. (April 2003), "Elemental abundance studies of CP stars. The helium-weak stars HD 19400, HD 34797 and HD 35456*", Astronomy and Astrophysics, 402: 331−334, Bibcode:2003A&A...402..331A, doi:10.1051/0004-6361:20030222.

[Barraza-7] Barraza, L. F.; et al. (2022). "Rotation Signature of TESS B-type Stars. A Comprehensive Analysis". The Astrophysical Journal. 924 (2): 117. arXiv:2202.01022. Bibcode:2022ApJ...924..117B. doi:10.3847/1538-4357/ac3335. S2CID 246030494.

[Gontcharov2012-8] 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 255202762.

[SIMBAD-9] "tet Hyi". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-10-13.{{cite web}}: CS1 maint: postscript (link)

[Hubrig2014-10] Hubrig, S.; et al. (August 2014), "Abundance analysis, spectral variability, and search for the presence of a magnetic field in the typical PGa star HD 19400", Monthly Notices of the Royal Astronomical Society, 442 (4): 3604−3615, arXiv:1406.1927, Bibcode:2014MNRAS.442.3604H, doi:10.1093/mnras/stu1122.

[Eggleton2008-11] Eggleton, P. P.; Tokovinin, A. A. (September 2008), "A catalogue of multiplicity among bright stellar systems", Monthly Notices of the Royal Astronomical Society, 389 (2): 869–879, arXiv:0806.2878, Bibcode:2008MNRAS.389..869E, doi:10.1111/j.1365-2966.2008.13596.x, S2CID 14878976.

[Shoeller2010-12] Schöller, M.; et al. (November 2010), "Multiplicity of late-type B stars with HgMn peculiarity", Astronomy and Astrophysics, 522: 12, arXiv:1010.3643, Bibcode:2010A&A...522A..85S, doi:10.1051/0004-6361/201014246, S2CID 119273467, A85

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Observation data Epoch J2000.0 Equinox J2000.0 (ICRS)
Constellation	Hydrus
Right ascension	03^h 02^m 15.449^s^[1]
Declination	−71° 54′ 08.84″^[1]
Apparent magnitude (V)	5.53^[2]
Characteristics
Spectral type	B8 III/IV^[3]
U−B color index	−0.51^[2]
B−V color index	−0.14^[2]
Astrometry

Radial velocity (R_v)	+12.3±1.6^[4] km/s
Proper motion (μ)	RA: +27.256 mas/yr^[1] Dec.: +16.598 mas/yr^[1]
Parallax (π)	6.4996±0.0619 mas^[1]
Distance	502 ± 5 ly (154 ± 1 pc)
Absolute magnitude (M_V)	−0.48^[5]

Details

Luminosity	287^[5] `L`_☉
Surface gravity (log g)	3.76^[6] cgs
Temperature	13,350^[6] K
Rotation	4.3720^[7] d
Age	211^[8] Myr

Other designations
θ Hyi, CPD−72°219, FK5 113, HD 19400, HIP 14131, HR 939, SAO 255945, WDS J03023-7154AB^[9]
Database references
SIMBAD	data

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