Eta2 Hydri

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Eta2 Hydri
Observation data
Epoch J2000.0      Equinox J2000.0
Constellation Hydrus
Right ascension 01h 54m 56.132s[1]
Declination –67° 38′ 50.29″[1]
Apparent magnitude (V) +4.68
Spectral type G8.5III
B−V color index 0.931
Variable type Suspected
Radial velocity (Rv) –16.2 km/s
Proper motion (μ) RA: 76.22 ± 0.14[1] mas/yr
Dec.: 72.94 ± 0.17[1] mas/yr
Parallax (π) 14.91 ± 0.16[1] mas
Distance 219 ± 2 ly
(67.1 ± 0.7 pc)
Absolute magnitude (MV) 0.57 ± 0.07[2]
Mass 1.87 ± 0.30[2] M
Radius 10.2 ± 0.5[2] R
Surface gravity (log g) 2.66 ± 0.10[2] cgs
Temperature 4,975[2] K
Metallicity [Fe/H] –0.21[2] dex
Age 1.30 ± 0.48[2] Gyr
Other designations
CPD−68 101, HD 11977, HIP 8928, HR 570, SAO 248460
Database references

Eta2 Hydri2 Hyi, η2 Hydri), often catalogued as HD 11977, is a giant yellow star approximately 219[1] light-years away in the constellation of Hydrus. Based on its mass, it was probably a class A star (similar to Vega or Fomalhaut) when it was on the main sequence, though it is now in the giant stage of its evolution. It is thought to be around 1.3 billion years old and has expanded to 10 times the Sun's diameter, though is only around 1.8 times as massive as the Sun.[2] As of 2005, an extrasolar planet was confirmed to be orbiting the star.

Planetary system[edit]

In 2005, the giant planet Eta2 Hydri b was found in orbit around Eta2 Hydri.[3]

The Eta2 Hydri planetary system[3]
(in order from star)
Mass Semimajor axis
Orbital period
Eccentricity Inclination Radius
b >6.54 MJ 1.93 711±8 0.40±0.07

See also[edit]


  1. ^ a b c d e f van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752Freely accessible. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. Vizier catalog entry
  2. ^ a b c d e f g h da Silva, L.; et al. (November 2006), "Basic physical parameters of a selected sample of evolved stars", Astronomy and Astrophysics, 458 (2): 609–623, arXiv:astro-ph/0608160Freely accessible, Bibcode:2006A&A...458..609D, doi:10.1051/0004-6361:20065105 
  3. ^ a b Setiawan; et al. (2005). "A substellar companion around the intermediate-mass giant star HD 11977". Astronomy & Astrophysics. 437 (2): L31–L34. arXiv:astro-ph/0505510Freely accessible. Bibcode:2005A&A...437L..31S. doi:10.1051/0004-6361:200500133. 

External links[edit]

Coordinates: Sky map 01h 54m 56s, −67° 38′ 50″