[ is located roughly 510 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.[18] It is moving away from the Sun with a radial velocity of +12.3 km/s.[7]]A stellar classification of B8 III/IV[4] suggests it is an evolving B-type star showing mixed traits of a subgiant or giant star. It is a PGa star – a higher temperature variety of the class of 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.[21] It is a helium-weak star, having helium lines that are anomalously weak for its spectral type.[13] A weak and variable longitudinal magnetic field has been detected.[21]
There is a nearby companion star of class A0 IV[24] 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,[25] although Eggleton and Tokovinin (2008) listed the pair as a probable binary star system.[24]
References
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