Eta2 Hydri

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**Eta² Hydri**
Observation data Equinox J2000.0
Constellation	Hydrus
Right ascension	01^h 54^m 56^m
Declination	-67° 38' 50"
Apparent magnitude (V)	+4.68
Characteristics
Spectral type	G8.5III
U-B color index	?
B-V color index	?
Variable type	none
Astrometry
Radial velocity (R_v)	-16.2 km/s
Proper motion (μ)	RA: 76.00 mas/yr Dec.: 73.17 mas/yr
Parallax (π)	15.04 ± .49 .40 1 mas
Distance	216.89 ly (66.53 pc)
Absolute magnitude (M_V)	+0.57
Details
Mass	1.91 M_☉
Radius	10.09 R_☉
Luminosity	? L_☉
Temperature	4970 K
Metallicity	-0.21 [Fe/H] 0.61
Rotation	230 d
Age	500 - 2000 Million years
Other designations
HD 11977, HR 570, HIP 8928....

Eta² Hydri (η² Hyi / η² Hydri) is a yellow giant star approximately 216 light-years away in the constellation 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.

[edit] Eta² Hydri b

**Eta² Hydri** b
Orbital elements
Extrasolar planet		Lists of extrasolar planets
Semimajor axis	(a)	1.93 AU
Eccentricity	(e)	0.40±0.07
Orbital period	(P)	711±8 d
Inclination	(i)	?°
Longitude of periastron	(ω)	351.5±9.5°
Time of periastron	(τ)	2,451,420 JD
Physical characteristics
Mass	(m)	>6.54 M_J
Radius	(r)	? R_J
Density	(ρ)	? kg/m³
Temperature	(T)	? K
Discovery information
Discovery date		2005
Discoverer(s)		Hatzes et al.
Detection method		Radial velocity
Discovery status		Published

Eta² Hydri b (also known as HD 11977 b) is an extrasolar planet orbiting Eta² Hydri. The presence of the planet around an intermediate-mass giant star provides indirect evidence for the existence of planetary systems around A-type stars.

[edit] References

Setiawan, J., Rodmann, J., da Silva, L., Hatzes, A., Pasquini, L., von der Lühe, O., de Medeiros, J., Döllinger, M., Girardi, L. (2005). "A substellar companion around the intermediate-mass giant star HD 11977". Astronomy & Astrophysics 437: L31 – L34.