Theta Hydrae

Theta Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 09h 14m 21.866s
Declination +02° 18′ 51.64″
Apparent magnitude (V) 3.888
Characteristics
Spectral type B9.5 V + DA 1.6
U−B color index −0.118
B−V color index −0.065
Astrometry
Radial velocity (Rv)−10.7±0.3 km/s
Proper motion (μ) RA: +128.152 mas/yr
Dec.: −327.709 mas/yr
Parallax (π)28.4019 ± 0.3682 mas
Distance115 ± 1 ly
(35.2 ± 0.5 pc)
Absolute magnitude (MV)+0.92
Details
θ Hya A
Mass2.52 M☉
Luminosity52 L☉
Surface gravity (log g)3.80±0.08 cgs
Temperature10,099±145 K
Metallicity [Fe/H]−0.42±0.09 dex
Rotational velocity (v sin i)95 km/s
θ Hya B
Mass0.68 or 1.21 M☉
Temperature30,700 K
Other designations
θ Hya, 22 Hydrae, BD+02°2167, FK5 347, HD 79469, HIP 45336, HR 3665, SAO 117527
Database references
SIMBADdata

Theta Hydrae, Latinized from θ Hydrae, is a binary star system in the constellation Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.9. The star system has a high proper motion with an annual parallax shift of 28.4 mas, indicating a distance of about 115 light years. Theta Hydrae forms a double with a magnitude 9.9 star located at an angular separation of 29 arcseconds.

The primary component of this system is a B-type main sequence star with a stellar classification of B9.5 V. It is a candidate Lambda Boötis star, indicating it displays an underabundance of iron peak elements. However, it is also underabundant in oxygen, a characteristic not shared by other Lambda Boötis stars. Instead, it may be a peculiar B star.

An orbiting white dwarf companion was discovered in 1998 from its X-ray emission. This degenerate star must have evolved from a progenitor that was once more massive than the current primary. Burleigh and Barstow (1999) gave a mass estimate of 0.68 times the mass of the Sun, whereas Holberg et al. (2013) put it as high as 1.21 times the Sun's mass. The latter would put it beyond the theoretical upper limit for white dwarf remnants of typical single stars that did not undergo a merger or mass loss.

References

  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.
  2. ^ a b c d Cousins, A. W. J. (1984), "Standardization of Broadband Photometry of Equatorial Standards", South African Astronomical Observatory Circulars, 8: 59, Bibcode:1984SAAOC...8...59C.
  3. ^ a b c d e f Holberg, J. B.; et al. (November 2013), "Where are all the Sirius-like binary systems?", Monthly Notices of the Royal Astronomical Society, 435 (3): 2077–2091, arXiv:1307.8047, Bibcode:2013MNRAS.435.2077H, doi:10.1093/mnras/stt1433.
  4. ^ Gontcharov, G. A. (November 2006), "Pulkovo Compilation of Radial Velocities for 35,495 Hipparcos stars in a common system", Astronomy Letters, 32 (11): 759–771, arXiv:1606.08053, Bibcode:2006AstL...32..759G, doi:10.1134/S1063773706110065, S2CID 119231169.
  5. ^ 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 119257644.
  6. ^ a b c Wu, Yue; et al. (January 2011), "Coudé-feed stellar spectral library – atmospheric parameters", Astronomy and Astrophysics, 525: A71, arXiv:1009.1491, Bibcode:2011A&A...525A..71W, doi:10.1051/0004-6361/201015014, S2CID 53480665.
  7. ^ Zorec, J.; Royer, F. (January 2012), "Rotational velocities of A-type stars. IV. Evolution of rotational velocities", Astronomy & Astrophysics, 537: A120, arXiv:1201.2052, Bibcode:2012A&A...537A.120Z, doi:10.1051/0004-6361/201117691, S2CID 55586789.
  8. ^ a b c d e Burleigh, M. R.; Barstow, M. A. (January 1999), "Theta Hya: spectroscopic identification of a second B star+white dwarf binary", Astronomy and Astrophysics, 341: 795–798, arXiv:astro-ph/9810113, Bibcode:1999A&A...341..795B.
  9. ^ "tet Hya". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2017-01-04.{{cite web}}: CS1 maint: postscript (link)
  10. ^ Privett, Grant; Jones, Kevin (2013), The Constellation Observing Atlas, The Patrick Moore Practical Astronomy Series, Springer Science & Business Media, p. 104, Bibcode:2013coa..book.....P, ISBN 978-1461476481.
  11. ^ King, J. R. (July 1994), "Accretion from Circumstellar Discs and the Lambda-Bootis Phenomenon", Monthly Notices of the Royal Astronomical Society, 269 (1): 209–217, Bibcode:1994MNRAS.269..209K, doi:10.1093/mnras/269.1.209.
  12. ^ Baschek, Bodo; Searle, Leonard (February 1969), "The Chemical Composition of the Lambda Bootis Stars", Astrophysical Journal, 155: 537, Bibcode:1969ApJ...155..537B, doi:10.1086/149890.
  13. ^ Vennes, S.; Kawka, A. (September 2008), "On the empirical evidence for the existence of ultramassive white dwarfs", Monthly Notices of the Royal Astronomical Society, 389 (3): 1367–1374, arXiv:0806.4742, Bibcode:2008MNRAS.389.1367V, doi:10.1111/j.1365-2966.2008.13652.x, S2CID 15349194.
  • Kaler, James B. (May 8, 2015), "Theta Hydrae", Stars, University of Illinois, retrieved 2016-01-04.