12 Hydrae
Star in the constellation Hydra
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12 Hydrae is a probable astrometric binary[10] star system located 205 light years away from the Sun in the equatorial constellation of Hydra. It has the Bayer designation D Hydrae;[9] 12 Hydrae is the Flamsteed designation. This system is visible to the naked eye as a faint, yellow-hued star with a combined apparent visual magnitude of 4.32.[1] It is moving closer to the Earth with a heliocentric radial velocity of −8.5 km/s.[1]
 | |
| Observation data Epoch J2000 Equinox J2000 | |
|---|---|
| Constellation | Hydra[1] |
| Right ascension | 08h 46m 22.54441s[2] |
| Declination | −13° 32′ 51.8051″[2] |
| Apparent magnitude (V) | 4.32[1] |
| Characteristics | |
| Evolutionary stage | red giant branch[2] |
| Spectral type | G8 IIIb CN-1[3] |
| B−V color index | 0.900±0.015[1] |
| Astrometry | |
| Radial velocity (Rv) | −8.5±0.7[1] km/s |
| Proper motion (μ) | RA: +10.316[2] mas/yr Dec.: −15.012[2] mas/yr |
| Parallax (π) | 15.8840±0.3987 mas[2] |
| Distance | 205 ± 5 ly (63 ± 2 pc) |
| Absolute magnitude (MV) | +0.26[4] |
| Orbit[5] | |
| Primary | Aa |
| Name | Ab |
| Period (P) | 1,592±806 d |
| Semi-major axis (a) | 0.0116±0.057″ |
| Eccentricity (e) | 0.40±0.26 |
| Inclination (i) | 58±10° |
| Longitude of the node (Ω) | 91±16° |
| Periastron epoch (T) | 49,194±664 |
| Argument of periastron (ω) (secondary) | 103±34° |
| Details | |
| Mass | 1.83[6] M☉ |
| Radius | 10.8[7] R☉ |
| Luminosity | 71[8] L☉ |
| Surface gravity (log g) | 3.13[6] cgs |
| Temperature | 5,105[7] K |
| Metallicity [Fe/H] | −0.01[6] dex |
| Rotational velocity (v sin i) | 4.6±0.2[4] km/s |
| Age | 410[2] Myr |
| Other designations | |
| D Hya, 12 Hya, BD−13°2673, HD 74918, HIP 43067, HR 3484, SAO 154622, WDS J08464-1333[9] | |
| Database references | |
| SIMBAD | data |
This was found to be a double star by R. A. Rossiter in 1953,[11] with the magnitude 13.7 companion having an angular separation of 26.8″ along a position angle of 266°, as of 2016. The brighter, magnitude 4.32 component A is a spectroscopic binary. As of 2009, the orbital solution for this pair is of low quality, giving a period of roughly 4 years and an eccentricity of around 0.4.[5]
The primary component is an aging giant star with a stellar classification of G8 IIIb CN-1,[3] where the suffix notation indicates an underabundance of the cyanogen molecule. It is 410 million years old[2] with 1.8 times the mass of the Sun.[6] After exhausting the hydrogen at its core and evolving off the main sequence, the star has swollen to 11 times the Sun's radius.[7] It is radiating 71 times the luminosity of the Sun[8] from its enlarged photosphere at an effective temperature of 5,105 K.[7]