Astronomy:Theta Hydri

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Short description: Star in the constellation Hydrus
Theta Hydri
Observation data
Equinox J2000.0]] (ICRS)
Constellation Hydrus
Right ascension  03h 02m 15.449s[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 (Rv)+12.3±1.6[4] km/s
Proper motion (μ) RA: +27.256[1] mas/yr
Dec.: +16.598[1] mas/yr
Parallax (π)6.4996 ± 0.0619[1] mas
Distance502 ± 5 ly
(154 ± 1 pc)
Absolute magnitude (MV)−0.48[5]
Details
Luminosity287[5] L
Surface gravity (log g)3.76[6] cgs
Temperature13,350[6] K
Rotation4.3720[7] d
Age211[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
SIMBADdata

Theta Hydri, Latinized from θ Hydri, is the Bayer designation for 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] is located approximately 502 light years from the Sun. 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

  1. Jump up to: 1.0 1.1 1.2 1.3 1.4 Brown, A. G. A. (2021). "Gaia Early Data Release 3: Summary of the contents and survey properties". Astronomy & Astrophysics 649: A1. doi:10.1051/0004-6361/202039657. Bibcode2021A&A...649A...1G.  Gaia EDR3 record for this source at VizieR.
  2. Jump up to: 2.0 2.1 2.2 2.3 Johnson, H. L. et al. (1966), "UBVRIJKL photometry of the bright stars", Communications of the Lunar and Planetary Laboratory 4 (99): 99, Bibcode1966CoLPL...4...99J. 
  3. Jump up to: 3.0 3.1 Houk, N.; Cowley, A. P. (1975), Michigan catalogue of two-dimensional spectral types for the HD stars, 1, Ann Arbor, Michigan: Dept. of Astronomy, University of Michigan, Bibcode1975mcts.book.....H. 
  4. Jump up to: 4.0 4.1 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, doi:10.1051/0004-6361/201219219, A61, Bibcode2012A&A...546A..61D. 
  5. Jump up to: 5.0 5.1 Anderson, E.; Francis, Ch. (2012), "XHIP: An extended hipparcos compilation", Astronomy Letters 38 (5): 331, doi:10.1134/S1063773712050015, Bibcode2012AstL...38..331A. 
  6. Jump up to: 6.0 6.1 6.2 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, doi:10.1051/0004-6361:20030222, Bibcode2003A&A...402..331A. 
  7. Barraza, L. F. et al. (2022). "Rotation Signature of TESS B-type Stars. A Comprehensive Analysis". The Astrophysical Journal 924 (2): 117. doi:10.3847/1538-4357/ac3335. Bibcode2022ApJ...924..117B. 
  8. Jump up to: 8.0 8.1 Gontcharov, G. A. (November 2012), "Spatial distribution and kinematics of OB stars", Astronomy Letters 38 (11): 694−706, doi:10.1134/S1063773712110035, Bibcode2012AstL...38..694G. 
  9. "tet Hyi". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=tet+Hyi. 
  10. Jump up to: 10.0 10.1 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, doi:10.1093/mnras/stu1122, Bibcode2014MNRAS.442.3604H. 
  11. Jump up to: 11.0 11.1 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, doi:10.1111/j.1365-2966.2008.13596.x, Bibcode2008MNRAS.389..869E. 
  12. Schöller, M. et al. (November 2010), "Multiplicity of late-type B stars with HgMn peculiarity", Astronomy and Astrophysics 522: 12, doi:10.1051/0004-6361/201014246, A85, Bibcode2010A&A...522A..85S