Tau1 Hydrae

For other stars with this Bayer designation, see τ Hydrae.
Tau1 Hydrae
Observation data
Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation Hydra
Right ascension 09h 29m 08.89655s[1]
Declination −02° 46′ 08.2649″[1]
Apparent magnitude (V) +4.59 (4.60 + 7.15)[2]
Characteristics
Spectral type F6 V + ? + K0[3]
B−V color index +0.411±0.015[2]
Astrometry
Radial velocity (Rv)+10.85±0.28[4] km/s
Absolute magnitude (MV)+3.28[5]
τ1 Hydrae A
Proper motion (μ) RA: +107.115[6] mas/yr
Dec.: −29.652[6] mas/yr
Parallax (π)56.2938 ± 0.5309 mas[6]
Distance57.9 ± 0.5 ly
(17.8 ± 0.2 pc)
τ1 Hydrae B
Proper motion (μ) RA: +138.487[7] mas/yr
Dec.: −17.371[7] mas/yr
Parallax (π)55.3675 ± 0.0638 mas[7]
Distance58.91 ± 0.07 ly
(18.06 ± 0.02 pc)
Orbit[8]
Period (P)2,807±23 d
Eccentricity (e)0.33±0.12
Periastron epoch (T)2445260 ± 150 JD
Semi-amplitude (K1)
(primary)		2.98±0.39 km/s
Details
τ1 Hydrae A
Mass1.20[9] M☉
Radius1.4[10] R☉
Luminosity (bolometric)3.369[2] L☉
Surface gravity (log g)4.12±0.14[9] cgs
Temperature6,473±220[9] K
Metallicity [Fe/H]−0.01[2] dex
Rotational velocity (v sin i)30.4±1.5[5] km/s
Age3.61[2] Gyr
τ1 Hydrae B
Mass0.86[11] M☉
Radius0.81[10] R☉
Luminosity0.435[7] L☉
Temperature5,197[7] K
Other designations
τ1 Hya, 31 Hydrae, BD−02°2901, GJ 348, HD 81997, HIP 46509, HR 3759, SAO 136895, WDS J09291-0246[12]
Database references
SIMBADτ1 Hya AB
τ1 Hya A
τ1 Hya B

Tau1 Hydrae is a triple star[3] system in the equatorial constellation of Hydra. Based upon the annual parallax shift of the two visible components as seen from Earth,[1] they are located about 18 parsecs (59 ly) from the Sun. The system has a combined apparent visual magnitude of +4.59,[2] which is bright enough to be visible to the naked eye at night.

The inner pair of stars form a single-lined spectroscopic binary with an orbital period of about 2,807 days and an eccentricity of 0.33.[8] The visible member of the pair, component A, is a visual magnitude 4.60[2] F-type main sequence star with a stellar classification of F6 V.[3] During the 1990s, it was thought to be a Gamma Doradus variable, but this was later discounted as it shows no short-term photometric variability. The star does show some long-term variability, possibly as a result of a magnetic activity cycle similar to the solar cycle.[13]

The tertiary member, component B, is a visual magnitude 7.15[2] K-type star with a class of K0.[3] It lies at a separation of 1,120 AU from the primary.[14] As of 2012, it was positioned at an angular separation of 67.5 arc seconds along a position angle of 4°.[15]

  1. ^ a b c Cite error: The named reference vanLeeuwen2007 was invoked but never defined (see the help page).
  2. ^ a b c d e f g h Cite error: The named reference Montesinos2016 was invoked but never defined (see the help page).
  3. ^ a b c d Cite error: The named reference Eggleton2008 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference deBruijne2012 was invoked but never defined (see the help page).
  5. ^ a b Cite error: The named reference Reiners2006 was invoked but never defined (see the help page).
  6. ^ a b c Cite error: The named reference dr2a was invoked but never defined (see the help page).
  7. ^ a b c d e Cite error: The named reference dr2b was invoked but never defined (see the help page).
  8. ^ a b Cite error: The named reference Pourbaiz2004 was invoked but never defined (see the help page).
  9. ^ a b c Cite error: The named reference David2015 was invoked but never defined (see the help page).
  10. ^ a b Cite error: The named reference PasinettiFracassini2001 was invoked but never defined (see the help page).
  11. ^ Cite error: The named reference Tokovinin2014 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference SIMBAD was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference Henry1999 was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Allen2012 was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference WDSC2014 was invoked but never defined (see the help page).