HD 22781

HD 22781, is a single star about 106 light-years away. It is a K-type main-sequence star. The star’s age is poorly constrained at 4.14±3.63 billion years, but is likely similar to that of the Sun.^[6] HD 22781 is heavily depleted in heavy elements, having just 45% of Sun's concentration of iron,^[3] yet is comparatively rich in carbon, having 90% of Sun`s abundance.^[6]

HD 22781

Observation data Epoch J2000      Equinox J2000
Constellation	Perseus[1]
Right ascension	03h 40m 49.5246s[2]
Declination	+31° 49′ 34.6489″[2]
Apparent magnitude (V)	8.78[3]
Characteristics
Evolutionary stage	main-sequence star[4]
Spectral type	K0[3]
Astrometry
Radial velocity (Rv)	8.26[2] km/s
Proper motion (μ)	RA: 40.576[2] mas/yr Dec.: −94.254[2] mas/yr
Parallax (π)	30.6433±0.1071 mas[5]
Distance	106.4 ± 0.4 ly (32.6 ± 0.1 pc)
Absolute magnitude (MV)	+6.21[1]
Details[6]
Mass	0.75±0.02 M☉
Radius	0.70±0.02 R☉
Surface gravity (log g)	4.57±0.04 cgs
Temperature	5175±15 K
Metallicity [Fe/H]	−0.35±0.02 dex
Rotational velocity (v sin i)	1.73[4] km/s
Age	4.14±3.63 Gyr
Other designations
BD+31 630, Gaia DR2 217334764042444288, HD 22781, HIP 17187, TYC 2355-246-1, GSC 02355-00246, 2MASS J03404953+3149345[2]
Database references
SIMBAD	data

An imaging survey in 2012 has failed to find any stellar companions, suggesting HD 22781 is a single star.^[7]

Planetary system

In 2011 a transiting superjovian planet or brown dwarf b was detected on an extremely eccentric orbit.^[4] It is located just outside of the conservative habitable zone of the parent star.^[8] Planets around such metal-poor stars are rare; the only three known similar cases are HD 111232 and HD 181720.^[9]

In 2012, a radial velocity data review indicated there are no additional giant planets in the system.^[10]

The HD 22781 planetary system^[4]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	≥13.65±0.97 MJ	1.167±0.039	528.07±0.14	0.8191±0.0023	—	—