51 Hydrae
Star in the constellation Hydra
From Wikipedia, the free encyclopedia
51 Hydrae is a single[7] star in the equatorial constellation of Hydra,[6] located 170 light years away from the Sun.[1] It has the Bayer designation k Hydrae; 51 Hydrae is the Flamsteed designation.[6] This object is visible to the naked eye as a faint, orange-hued star with an apparent visual magnitude of 4.78. It is moving further from the Earth with a heliocentric radial velocity of +20 km/s.[2] Eggen (1971) listed it as a member of the η Cephei group of old-disk stars.[8]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 14h 23m 05.77393s[1] |
| Declination | −27° 45′ 14.4609″[1] |
| Apparent magnitude (V) | 4.78[2] |
| Characteristics | |
| Evolutionary stage | giant |
| Spectral type | K4 III[3] |
| B−V color index | 1.300±0.040[2] |
| Astrometry | |
| Radial velocity (Rv) | 19.7±0.9[2] km/s |
| Proper motion (μ) | RA: −202.476[1] mas/yr Dec.: −117.186[1] mas/yr |
| Parallax (π) | 19.2042±0.2252 mas[1] |
| Distance | 170 ± 2 ly (52.1 ± 0.6 pc) |
| Absolute magnitude (MV) | 1.36[2] |
| Details | |
| Mass | 1.31[4] M☉ |
| Radius | 13.47+0.48 −1.26[1] R☉ |
| Luminosity | 54.9+0.8 −1.5[1] L☉ |
| Surface gravity (log g) | 2.25[5] cgs |
| Temperature | 4,255±31[4] K |
| Metallicity [Fe/H] | 0.08[5] dex |
| Other designations | |
| k Hya, 51 Hya, NSV 6648, CD−27°9803, HD 125932, HIP 70306, HR 5381, SAO 182483[6] | |
| Database references | |
| SIMBAD | data |
This is an evolved giant star with a stellar classification of K4 III,[3] which indicates it has exhausted the supply of hydrogen at its core and expanded off the main sequence. It has 1.31[4] times the mass of the Sun but has swollen to 13.5[1] times the Sun's radius. The star is radiating 55[1] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,255 K.[4]