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.
| 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 |
| Distance | 219 ± 2 ly (67.1 ± 0.7 pc) |
| Absolute magnitude (MV) | 0.57 ± 0.07[2] |
| Details | |
| 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 | |
| Database references | |
| SIMBAD | data |
Planetary system
In 2005, the giant planet Eta2 Hydri b was found in orbit around Eta2 Hydri.[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 | — | — |
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See also
References
- 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.Vizier catalog entry
- 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
- 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.
External links
- "Notes for star HD 11977". The Extrasolar Planets Encyclopaedia. Retrieved 2008-07-03.
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