HD 191939

HD 191939 is a single yellow (G-type) main-sequence star, located approximately 174 light-years away in the northern constellation of Draco, taking its primary name from its Henry Draper Catalogue designation.

HD 191939

Location of HD 191939 in the night sky. The star is marked within the red diamond.
Observation data Epoch J2000      Equinox J2000
Constellation	Draco[1]
Right ascension	20h 08m 05.75515s[2]
Declination	+66° 51′ 02.0766″[2]
Apparent magnitude (V)	8.971[3]
Characteristics
HD 191939
Evolutionary stage	main sequence[2]
Spectral type	G9V[4]
Astrometry
Radial velocity (Rv)	−9.23±0.16[2] km/s
Proper motion (μ)	RA: 150.194±0.015 mas/yr[2] Dec.: −63.988±0.017 mas/yr[2]
Parallax (π)	18.6967±0.0133 mas[2]
Distance	174.4 ± 0.1 ly (53.49 ± 0.04 pc)
Absolute magnitude (MV)	+5.17[1]
Details[4]
HD 191939
Mass	0.81±0.04 M☉
Radius	0.94±0.02 R☉
Luminosity (bolometric)	0.65±0.02 L☉
Surface gravity (log g)	4.3±0.1 cgs
Temperature	5348±100 K
Metallicity [Fe/H]	−0.15±0.06 dex
Rotational velocity (v sin i)	0.6±0.5[5] km/s
Age	7±3[5] Gyr
Other designations
Gaia DR2 2248126315275354496, HD 191939, HIP 99175, TOI-1339, TIC 269701147, TYC 4244-964-1, 2MASS J20080574+6651019[6]
Database references
SIMBAD	data
Exoplanet Archive	data

Characteristics

HD 191939 is a Sun-like G-type main-sequence star, likely older than the Sun and relatively depleted in metals.

Planetary system

In 2020, an analysis carried out by a team of astronomers led by astronomer Mariona Badenas-Agusti of the TESS project confirmed the existence of three gaseous planets, all smaller than Neptune, in orbit around HD 191939.^[5] Another non-transiting gas giant planet designated HD 191939 e was detected in 2021, along with a substellar object on a highly uncertain, 9 to 46 year orbit.^[4] In 2022, a sixth planet, with a mass comparable to Uranus, was discovered in the system's habitable zone.^[7] The 2021 study also suggested the possible presence of an additional non-transiting planet with a period of 17.7 days,^[4] but the 2022 study did not support this.^[7]

The HD 191939 planetary system^[7]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	10.00±0.70 M🜨	0.0804+0.0025 −0.0023	8.8803256	0.031+0.010 −0.011	88.10+0.14 −0.10°	3.410±0.075 R🜨
c	8.0±1.0 M🜨	0.1752+0.0055 −0.0050	28.579743	0.034+0.034 −0.013	89.10+0.06 −0.08°	3.195±0.075 R🜨
d	2.80±0.60 M🜨	0.2132+0.0065 −0.0061	38.353037	0.031+0.018 −0.012	89.49+0.05 −0.08°	2.995±0.070 R🜨
e	≥112.2±4.0 M🜨	0.407±0.012	101.12±0.13	0.031+0.008 −0.016	88.7±0.7[4]°	—
g	≥13.5±2.0 M🜨	0.812±0.028	284+10 −8	0.030+0.025 −0.011	—	—
f	>2.08 MJ	>3.2	>2200	—	—	—

See also

• List of extrasolar planets
• List of exoplanets discovered in 2020 (HD 191939 b, c and d)
• List of exoplanets discovered in 2021 (HD 191939 e)
• List of exoplanets discovered in 2022 (HD 191939 f & g)