Mu Hydrae
Star in the constellation Hydra
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μ Hydrae, Latinised as Mu Hydrae, is a solitary,[8] orange-hued star in the equatorial constellation of Hydra. It is visible to the naked eye with an apparent visual magnitude of 3.83.[2] Positioned just 1.8° to the south-southwest is the planetary nebula NGC 3242.[9] Mu Hydrae has an annual parallax shift of 13.93 mas,[1] which yields a distance estimate of 234 light years.
 | |
| Observation data Epoch J2000.0 Equinox J2000.0 (ICRS) | |
|---|---|
| Constellation | Hydra |
| Right ascension | 10h 26m 05.42630s[1] |
| Declination | −14° 19′ 56.2675″[1] |
| Apparent magnitude (V) | 3.83[2] |
| Characteristics | |
| Spectral type | K4 III[3] |
| U−B color index | +1.83[2] |
| B−V color index | +1.47[2] |
| Variable type | Suspected[4] |
| Astrometry | |
| Radial velocity (Rv) | +40.81±0.36[5] km/s |
| Proper motion (μ) | RA: −129.17[1] mas/yr Dec.: −79.76[1] mas/yr |
| Parallax (π) | 13.93±0.18 mas[1] |
| Distance | 234 ± 3 ly (71.8 ± 0.9 pc) |
| Absolute magnitude (MV) | −0.45[6] |
| Details[5] | |
| Radius | 45 R☉ |
| Luminosity | 332[6] L☉ |
| Surface gravity (log g) | 1.5 cgs |
| Temperature | 3,999±8 K |
| Metallicity [Fe/H] | −0.12 dex |
| Rotational velocity (v sin i) | 6.0 km/s |
| Other designations | |
| μ Hya, 42 Hydrae, BD−16°3052, FK5 389, HD 90432, HIP 51069, HR 4094, SAO 155980.[7] | |
| Database references | |
| SIMBAD | data |
This is an evolved K-type giant star with a stellar classification of K4 III,[3] having used up its core hydrogen and has expanded to around 45 times the radius of the Sun.[5] It is a suspected variable star, with a brightness that varies about 0.03 in magnitude.[4] The relatively cool outer atmosphere has an effective temperature of 3999 K.[5]