HD 221420

HD 221420 (HR 8935; Gliese 4340) is a likely binary star system^[7] in the southern circumpolar constellation Octans. It has an apparent magnitude of 5.81, allowing it to be faintly seen with the naked eye. The object is relatively close at a distance of 102 light years but is receding with a heliocentric radial velocity of 26.5 km/s.

HD 221420

Observation data Epoch J2000.0      Equinox J2000.0 (ICRS)
Constellation	Octans
Right ascension	23h 33m 19.5789s[1]
Declination	−77° 23′ 07.194″[1]
Apparent magnitude (V)	5.81±0.01[2]
Characteristics
Spectral type	G2 IV-V[3]
U−B color index	+0.31[4]
B−V color index	+0.68[4]
Astrometry
Radial velocity (Rv)	26.48±0.02[5] km/s
Proper motion (μ)	RA: +16.306 mas/yr[1] Dec.: +0.736 mas/yr[1]
Parallax (π)	32.1023±0.0325 mas[1]
Distance	101.6 ± 0.1 ly (31.15 ± 0.03 pc)
Absolute magnitude (MV)	+3.33[6]
Details
Mass	1.35±0.01[7] M☉
Radius	1.95±0.01[7] R☉
Luminosity	4.01±1[8] L☉
Surface gravity (log g)	4.03±0.03[7] cgs
Temperature	5,830±44[9] K
Metallicity [Fe/H]	+0.34±0.07[10] dex
Rotational velocity (v sin i)	2.8±0.5[11] km/s
Age	3.65±0.23[7] Gyr
Other designations
83 G. Octantis, CPD−78°1473, FK5 3887, GC 32742, GJ 4340, HD 221420, HIP 116250, HR 8935, SAO 258154[12][13]
Database references
SIMBAD	data
Exoplanet Archive	data

HD 221420 has a stellar classification of G2 IV-V,^[3] indicating a solar analogue with a luminosity class intermediate between a subgiant and a main sequence star. The object is also extremely chromospherically inactive.^[3] It has a comparable mass to the Sun and a diameter of 1.95 R_☉.^[7] It shines with a luminosity of 4 L_☉^[8] from its photosphere at an effective temperature of 5,830 K,^[9] giving a yellow glow. HD 221420 is younger than the Sun at 3.65 billion years.^[7] Despite this, the star is already beginning to evolve off the main sequence. Like most planetary hosts, HD 221420 has a metallicity over twice of that of the Sun^[7] and spins modestly with a projected rotational velocity 2.8 km/s.^[11]

There is a mid-M-dwarf star with a similar proper motion and parallax to HD 221420, which is likely gravitationally bound to it. The two stars are separated by 698 arcseconds, corresponding to a distance of 21,756 AU.^[7]

Planetary system

In a 2019 doppler spectroscopy survey, an exoplanet was discovered orbiting the star. The planet was originally thought to be a super Jupiter, having a minimum mass of 9.7 M_J.^[9] However, later observations using Hipparcos and Gaia astrometry found it to be a brown dwarf with a high-inclination orbit,^[7][10][14] revealing a true mass of 23 M_J.^[7]

The HD 221420 A planetary system^[7]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (years)	Eccentricity	Inclination	Radius
b	22.9±2.2 MJ	10.15+0.59 −0.38	27.62+2.45 −1.54	0.14+0.04 −0.03	164.0+1.9 −2.6°	—