| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra |
| Right ascension | 08h41m 43.33591s[1] |
| Declination | −15° 56′ 36.1727″[1] |
| Apparent magnitude (V) | 4.866[2] |
| Characteristics | |
| Spectral type | K0 III CNII[3] |
| U−B color index | +0.92[4] |
| B−V color index | +1.07[4] |
| Astrometry | |
| Radial velocity (Rv) | −1.98±0.12[1] km/s |
| Proper motion (μ) | RA: 3.676[1] mas/yr Dec.: -97.743[1] mas/yr |
| Parallax (π) | 15.9089 ± 0.1297 mas[1] |
| Distance | 205 ± 2 ly (62.9 ± 0.5 pc) |
| Absolute magnitude (MV) | +0.81[5] |
| Details[6] | |
| Mass | 1.72±0.46[7] M☉ |
| Radius | 11.10+0.15 −0.69[1] R☉ |
| Luminosity | 54.445+0.536 −0.457[1] 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 | |
9 Hya, BD−15°2554, FK5 2684, HD 74137, HIP 42662, HR 3441, SAO 154552[8] | |
| Database references | |
| SIMBAD | data |
9 Hydrae is a single[9] star in the equatorial constellationofHydra,[8] located 205 light years away from the Sun.[1] It is visible to the naked eye as a faint, yellow-orange hued star with an apparent visual magnitude of 4.87.[2] This body is moving closer to the Sun with a heliocentric radial velocity of −2 km/s.[1]
This is an aging giant star with a stellar classificationofK0 III CNII,[3] where the suffix notation indicates an overabundance of cyanogen in the spectrum. It is a red clump giant,[10] which indicates it is on the horizontal branch and is generating energy through helium fusion at its core. The star has 1.7[7] times the mass of the Sun but, as a consequence of evolving away from the main sequence, its envelope has swollen to 11[1] 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.[6]
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