Theta Hydri

Theta Hydri
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]
Distance502 ± 5 ly
(154 ± 1 pc)
Absolute magnitude (MV)−0.48[5]
Details
Luminosity287[5] L☉
Surface gravity (log g)3.76[6] cgs
Temperature13,350[6] K
Rotation4.3720[7] d
Age211[8] Myr
Other designations
θ Hyi, CPD−72°219, FK5 113, HD 19400, HIP 14131, HR 939, SAO 255945, WDS J03023-7154AB[9]
Database references
SIMBADdata

Theta Hydri, Latinized from θ Hydri, is 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] it is located approximately 502 light years. 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]

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]

  1. ^ a b c d e Cite error: The named reference GaiaEDR3 was invoked but never defined (see the help page).
  2. ^ a b c d Cite error: The named reference Johnson1966 was invoked but never defined (see the help page).
  3. ^ a b Cite error: The named reference houk1975 was invoked but never defined (see the help page).
  4. ^ a b Cite error: The named reference deBruijne2012 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 Alonso2003 was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference Barraza was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Gontcharov2012 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. ^ a b Cite error: The named reference Hubrig2014 was invoked but never defined (see the help page).
  11. ^ a b Cite error: The named reference Eggleton2008 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Shoeller2010 was invoked but never defined (see the help page).