Eta2 Hydri

Eta2 Hydri (η2 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.

For other stars with this Bayer designation, see η Hydri.
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
Characteristics
Spectral type G8.5III
B−V color index 0.931
Variable type Suspected
Astrometry
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
Distance219 ± 2 ly
(67.1 ± 0.7 pc)
Absolute magnitude (MV)0.57 ± 0.07[2]
Details
Mass1.87 ± 0.30[2] M☉
Radius10.2 ± 0.5[2] R☉
Surface gravity (log g)2.66 ± 0.10[2] cgs
Temperature4,975[2] K
Metallicity [Fe/H]–0.21[2] dex
Age1.30 ± 0.48[2] Gyr
Other designations
CPD−68 101, HD 11977, HIP 8928, HR 570, SAO 248460
Database references
SIMBADdata

Planetary system

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

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

See also

References
  1. van Leeuwen, F. (2007). "Validation of the new Hipparcos reduction". Astronomy and Astrophysics. 474 (2): 653–664. arXiv:0708.1752. Bibcode:2007A&A...474..653V. doi:10.1051/0004-6361:20078357. S2CID 18759600.Vizier catalog entry
  2. 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/0608160, Bibcode:2006A&A...458..609D, doi:10.1051/0004-6361:20065105, S2CID 9341088
  3. Setiawan; et al. (2005). "A substellar companion around the intermediate-mass giant star HD 11977". Astronomy & Astrophysics. 437 (2): L31–L34. arXiv:astro-ph/0505510. Bibcode:2005A&A...437L..31S. doi:10.1051/0004-6361:200500133. S2CID 6362483.

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