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Theta Hydrae

Theta Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 09h 14m 21.866s[1]
Declination +02° 18′ 51.64″[1]
Apparent magnitude (V) 3.888[2]
Characteristics
Spectral type B9.5 V + DA 1.6[3]
U−B color index −0.118[2]
B−V color index −0.065[2]
Astrometry
Radial velocity (Rv)−10.7±0.3[4] km/s
Proper motion (μ) RA: +128.152[1] mas/yr
Dec.: −327.709[1] mas/yr
Parallax (π)28.4019 ± 0.3682 mas[1]
Distance115 ± 1 ly
(35.2 ± 0.5 pc)
Absolute magnitude (MV)+0.92[5]
Details
θ Hya A
Mass2.52[3] M☉
Luminosity52[5] L☉
Surface gravity (log g)3.80±0.08[6] cgs
Temperature10,099±145[6] K
Metallicity [Fe/H]−0.42±0.09[6] dex
Rotational velocity (v sin i)95[7] km/s
θ Hya B
Mass0.68[8] or 1.21[3] M☉
Temperature30,700[3] K
Other designations
θ Hya, 22 Hydrae, BD+02°2167, FK5 347, HD 79469, HIP 45336, HR 3665, SAO 117527[9]
Database references
SIMBADdata

Theta Hydrae, Latinized from θ Hydrae, is a binary star[8] system in the constellation Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.9.[2] The star system has a high proper motion[8] with an annual parallax shift of 28.4 mas,[1] 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.[10]

The primary component of this system is a B-type main sequence star with a stellar classification of B9.5 V.[3] It is a candidate Lambda Boötis star, indicating it displays an underabundance of iron peak elements.[11] However, it is also underabundant in oxygen, a characteristic not shared by other Lambda Boötis stars. Instead, it may be a peculiar B star.[12]

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.[8] Burleigh and Barstow (1999) gave a mass estimate of 0.68[8] times the mass of the Sun, whereas Holberg et al. (2013) put it as high as 1.21[3] 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.[13]

  1. ^ a b c d e f Cite error: The named reference dr2 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference Cousins1984 was invoked but never defined (see the help page).
  3. ^ a b c d e f Cite error: The named reference Holberg2013 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Gontcharov2006 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Anderson2012 was invoked but never defined (see the help page).
  6. ^ a b c Cite error: The named reference Wu2011 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Zorec2012 was invoked but never defined (see the help page).
  8. ^ a b c d e Cite error: The named reference Burleigh1999 was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Privett2013 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference King1994 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Baschek1969 was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Vennes2008 was invoked but never defined (see the help page).
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