HD 109271

HD 109271 is a wide binary star system in the constellation of Virgo. The brighter member of the binary has a pair of orbiting exoplanets. With an apparent visual magnitude of 8.05,^[3] it cannot be seen with the naked eye. Parallax measurements made by Gaia put the star at a distance of 181 light-years (55 parsecs) away from the Sun, but it is drifting closer with a radial velocity of −5 km/s.^[5] The system shows a high proper motion, traversing the celestial sphere at an angular rate of 0.232 arcsec yr⁻¹.^[8]

HD 109271

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Virgo[1]
Right ascension	12h 33m 35.555s[2]
Declination	−11° 37′ 18.73″[2]
Apparent magnitude (V)	8.05 ± 0.01[3]
Characteristics
Spectral type	G5 V[3] + DA[4]
B−V color index	+0.658±0.002[3]
Astrometry
Radial velocity (Rv)	−4.971±0.0011[5] km/s
Proper motion (μ)	RA: −169.971 mas/yr[2] Dec.: 81.000 mas/yr[2]
Parallax (π)	17.9082±0.0379 mas[2]
Distance	182.1 ± 0.4 ly (55.8 ± 0.1 pc)
Absolute magnitude (MV)	4.1±0.1[3]
Position (relative to HD 109271 A)[4]
Component	HD 109271 B
Epoch of observation	2018
Angular distance	5.425″
Position angle	267.354°
Projected separation	304 AU
Details[3]
HD 109271 A
Mass	1.047±0.024 M☉
Radius	1.295+0.023 −0.020[6] R☉
Luminosity	1.649±0.008[6] L☉
Surface gravity (log g)	4.28±0.10 cgs
Temperature	5,783±62 K
Metallicity [Fe/H]	0.10±0.05 dex
Rotational velocity (v sin i)	2.7 km/s
Age	7.3±1.2 Gyr
HD 109271 B
Mass	~0.6[4] M☉
Other designations
BD−10°3494, HD 109271, HIP 61300, SAO 157362, LTT 4770[7]
Database references
SIMBAD	data
Exoplanet Archive	data

The primary component is an ordinary G-type main-sequence star with a stellar classification of G5 V. It is a much older star than the Sun with an age of about 7.3 billion years, and is spinning with a projected rotational velocity of 2.7 km/s.^[3] This star has 7% more mass than the Sun and a 30% greater girth.^[6] The abundance of iron, a measure of the star's metallicity, is similar but slightly higher than in the Sun.^[3] It is radiating 1.65^[6] times the luminosity of the Sun from its photosphere at an effective temperature of around 5,783 K.^[3]

In 2020, a white dwarf companion of 0.6 M_☉ was found orbiting the primary at an angular separation of 5.4″ along a position angle of 267°. At the distance of this system, this corresponds to a projected separation of 304 AU. That is, they are physically separated by at least this distance. Additional stellar companions are ruled out down to a separation of 0.15″ from the primary.^[4]

Planetary system

From 2003 to 2012, the star was under observance from the High Accuracy Radial Velocity Planet Searcher (HARPS).^[3] In 2012, two eccentric hot Neptune-mass planets were deduced by radial velocity. They were published in January 2013. These are close to a 1:4 resonance, so the system is similar to HD 69830. A third Neptune in the Venus zone was hypothesised from the data. These planets managed to survive the post main-sequence epoch of the companion star, when it shed much of its original mass.^[4]

The HD 109271 planetary system^[9][3]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	>0.054 ± 0.004 MJ	0.079 ± 0.001	7.8543 ± 0.0009	0.25 ± 0.08	—	—
c	>0.076 ± 0.007 MJ	0.196 ± 0.003	30.93 ± 0.02	0.15 ± 0.09	—	—
d (unconfirmed)	>1.3 neptune MJ	1	430	0.36	—	—