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]
Observation data Epoch J2000.0 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 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 (MV) | −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 | |
Database references | |
SIMBAD | data |
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]
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