9 Hydrae
9 Hydrae is a single star in the equatorial constellation of Hydra, located 205 light years away from the Sun. It is visible to the naked eye as a faint, yellow-orange hued star with an apparent visual magnitude of 4.87. This body is moving closer to the Sun with a heliocentric radial velocity of −2 km/s.
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 08h 41m 43.33591s |
| Declination | −15° 56′ 36.1727″ |
| Apparent magnitude (V) | 4.866 |
| Characteristics | |
| Spectral type | K0 III CNII |
| U−B color index | +0.92 |
| B−V color index | +1.07 |
| Astrometry | |
| Radial velocity (Rv) | −1.98±0.12 km/s |
| Proper motion (μ) | RA: 3.676 mas/yr Dec.: -97.743 mas/yr |
| Parallax (π) | 15.9089 ± 0.1297 mas |
| Distance | 205 ± 2 ly (62.9 ± 0.5 pc) |
| Absolute magnitude (MV) | +0.81 |
| Details | |
| Mass | 1.72±0.46 M☉ |
| Radius | 11.10+0.15 −0.69 R☉ |
| Luminosity | 54.445+0.536 −0.457 L☉ |
| Surface gravity (log g) | 2.8 cgs |
| Temperature | 4,688±5 K |
| Metallicity [Fe/H] | −0.01 dex |
| Rotational velocity (v sin i) | 1.7 km/s |
| Other designations | |
| Database references | |
| SIMBAD | data |
This is an aging giant star with a stellar classification of K0 III CNII, where the suffix notation indicates an overabundance of cyanogen in the spectrum. It is a red clump giant, which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. The star has 1.7 times the mass of the Sun but, as a consequence of evolving away from the main sequence, its envelope has swollen to 11 times the Sun's radius. It is radiating 54 times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,688 K.