HD 159868

HD 159868 is a star in the southern constellation of Scorpius, positioned about 0.3° to the ESE of the bright star Theta Scorpii.^[11] With an apparent visual magnitude of +7.24,^[3] it is too faint to be visible to the naked eye but can be viewed with a small telescope. The star lies at a distance of 182 light years from the Sun based on parallax, but is drifting closer with a radial velocity of −24 km/s.^[3]

HD 159868

Observation data Epoch J2000      Equinox J2000
Constellation	Scorpius[1]
Right ascension	17h 38m 59.5269s[2]
Declination	−43° 08′ 43.842″[2]
Apparent magnitude (V)	+7.24[3]
Characteristics
Spectral type	G5V[4]
Apparent magnitude (J)	5.941±0.021[5]
Apparent magnitude (H)	5.567±0.026[5]
Apparent magnitude (K)	5.535±0.024[5]
B−V color index	0.714±0.012[3]
Astrometry
Radial velocity (Rv)	−23.80±0.76[3] km/s
Proper motion (μ)	RA: −230.824[2] mas/yr Dec.: −167.903[2] mas/yr
Parallax (π)	17.8754±0.0207 mas[2]
Distance	182.5 ± 0.2 ly (55.94 ± 0.06 pc)
Absolute magnitude (MV)	+3.63[6]
Details
Mass	1.123±0.018[7] M☉
Radius	1.97±0.04 R☉[7] R☉
Luminosity	3.82[8] L☉
Surface gravity (log g)	3.96±0.02[6] cgs
Temperature	5,558±15[6] K
Metallicity [Fe/H]	−0.08±0.01[6] dex
Rotation	7.26[9] days
Rotational velocity (v sin i)	2.1[6] km/s
Age	6.6±0.2[7] Gyr
Other designations
CD−43°11901, GJ 4014, HD 159868, HIP 86375, SAO 228234[10]
Database references
SIMBAD	data

Properties

The spectrum of HD 159868 matches a G-type main-sequence star with a stellar classification of G5V. It has a relatively low surface gravity for its class, which suggests it is slightly evolved off the main sequence. The star is chromospherically inactive with a slow rotation rate, having a projected rotational velocity of 2.1 km/s.^[6] It is an estimated 6.6 billion years old with 8–12% more mass than the Sun and nearly double the Sun's radius. The star is radiating 3.8 times the luminosity of the Sun from its photosphere at an effective temperature of 5,558 K.

Planetary system

In 2007, a planet of the star was announced by astronomer Simon J. O'Toole and collaborators.^[12] The planet (designated HD 159868 b) is likely to be a gas giant. Preliminary orbital elements suggested the orbit is extremely eccentric at the average distance of 2 astronomical units (AU), ranging as close as 0.62 AU to as far as 3.38 AU. In 2012, a second planet of the star was announced by astronomer Robert A. Wittenmyer and associates. The orbit of the first planet was significantly revised during the investigation.^[6]

The HD 159868 planetary system^[12][6]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
c	≥0.73±0.05 MJ	1.00±0.01	352.3±1.3	0.15±0.05	—	—
b	≥2.1±0.1 MJ	2.25±0.03	1,178.4±8.8	0.01±0.03	—	—

See also

• HD 219828
• HD 28185
• List of extrasolar planets