12 Hydrae

12 Hydrae is a probable astrometric binary^[8] star system located 202 light years away from the Sun in the equatorial constellation of Hydra. It has the Bayer designation D Hydrae;^[7] 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.^[2] It is moving closer to the Earth with a heliocentric radial velocity of −8.5 km/s.^[2]

12 Hydrae

Observation data Epoch J2000      Equinox J2000
Constellation	Hydra
Right ascension	08h 46m 22.53544s[1]
Declination	−13° 32′ 51.7502″[1]
Apparent magnitude (V)	4.32[2]
Characteristics
Spectral type	G8 IIIb CN-1[3]
B−V color index	0.900±0.015[2]
Astrometry
Radial velocity (Rv)	−8.5±0.7[2] km/s
Proper motion (μ)	RA: +18.789[1] mas/yr Dec.: −18.385[1] mas/yr
Parallax (π)	16.1839±0.6646 mas[1]
Distance	202 ± 8 ly (62 ± 3 pc)
Absolute magnitude (MV)	+0.26[4]
Orbit[5]
Primary	Aa
Companion	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	2.32[6] M☉
Radius	11.51+0.18 −0.37[1] R☉
Luminosity	77.468±3.553[1] L☉
Temperature	4,968±13[6] K
Rotational velocity (v sin i)	4.6±0.2[4] km/s
Age	910[6] Myr
Other designations
D Hya, 12 Hya, BD−13°2673, HD 74918, HIP 43067, HR 3484, SAO 154622, WDS J08464-1333[7]
Database references
SIMBAD	data

This was found to be a double star by R. A. Rossiter in 1953,^[9] 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 910^[6] million years old with 2.32^[6] times the mass of the Sun. After exhausting the hydrogen at its core and evolving off the main sequence, the star has swollen to 11.5^[1] times the Sun's radius. It is radiating 77^[1] times the luminosity of the Sun from its enlarged photosphere at an effective temperature of 4,968 K.^[6]