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]
Distance
115 ± 1 ly (35.2 ± 0.5 pc)
Absolute magnitude (MV)
+0.92[5]
Details
θ Hya A
Mass
2.52[3]M☉
Luminosity
52[5]L☉
Surface gravity (log g)
3.80±0.08[6] cgs
Temperature
10,099±145[6] K
Metallicity [Fe/H]
−0.42±0.09[6] dex
Rotational velocity (v sin i)
95[7] km/s
θ Hya B
Mass
0.68[8] or 1.21[3]M☉
Temperature
30,700[3] K
Other designations
θ Hya, 22 Hydrae, BD+02°2167, FK5 347, HD 79469, HIP 45336, HR 3665, SAO 117527[9]
Database references
SIMBAD
data
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]
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^ abcdefCite error: The named reference Holberg2013 was invoked but never defined (see the help page).
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^ abCite error: The named reference Anderson2012 was invoked but never defined (see the help page).
^ abcCite error: The named reference Wu2011 was invoked but never defined (see the help page).
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^ abcdeCite error: The named reference Burleigh1999 was invoked but never defined (see the help page).
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^Cite error: The named reference Privett2013 was invoked but never defined (see the help page).
^Cite error: The named reference King1994 was invoked but never defined (see the help page).
^Cite error: The named reference Baschek1969 was invoked but never defined (see the help page).
^Cite error: The named reference Vennes2008 was invoked but never defined (see the help page).
ThetaHydrae, 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...
Omega Hydrae, Latinised from ω Hydrae, is a golden-hued star in the equatorial constellation of Hydra, located to the west-southwest of the brighter star...
Albireo Double star 3.10 Zeta Hydrae Star 3.11 3.05 Eta Sagittarii Binary star system 3.11 Alpha Indi Star 3.11 Nu Hydrae Star 3.11 Kappa Centauri Binary...
Solar-Like Oscillations, Observational Constraints, and Stellar Models for $\theta$ Cyg, the Brightest Star Observed by the {\it Kepler} Mission". The Astrophysical...
heliosphere. In 2006, a far infrared bow shock was detected near the AGB star R Hydrae. Bow shocks are also a common feature in Herbig Haro objects, in which a...
1889 1889 Mato Grosso do Sul Alpha Hydrae (Alphard) Hydra, the Water Serpent 2 1979[note] 1960[note] Acre Gamma Hydrae Hydra, the Water Serpent 3 1962 1968...
Lambda Crateris, Nu Hydrae, Eta Crateris, Delta Crateris, Iota Crateris, Kappa Crateris, Epsilon Crateris, HD 95808, HD 93833, Theta Crateris, HD 102574...
Model-Theoretic Approach to Ordinal Analysis" (1997). M. Rathjen, W. Carnielli, "Hydrae and subsystems of arithmetic" (1991) Jeroen Van der Meeren; Rathjen, Michael;...
النِّطَاق Zeta Orionis Alphard al-Fard the Solitary one الفرد الفَرْد Alpha Hydrae Alphecca (Nayyir) al-Fakkah (the Bright one of) the Broken (Ring) نير الفكة...
light-years (25 parsecs) distant from the Sun. It is a candidate member of the TW Hydrae association of co-moving stars. Zeta Aquilae's two components can be designated...