TOI-2109

TOI-2109 is a magnitude 10.2 star in the constellation of Hercules. It is located 870 ly (268 pc) from Earth based on parallax measurements. This star is host to one confirmed exoplanet.

TOI-2109

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Hercules[1]
Right ascension	16h 52m 44.72027s[2]
Declination	+16° 34′ 47.8400″[2]
Apparent magnitude (V)	10.22±0.03[3]
Characteristics
Evolutionary stage	Main sequence[4]
Spectral type	F[4]
Astrometry
Radial velocity (Rv)	−22.28±1.23[2] km/s
Proper motion (μ)	RA: −8.314 mas/yr[2] Dec.: −9.351 mas/yr[2]
Parallax (π)	3.7367±0.0197 mas[2]
Distance	873 ± 5 ly (268 ± 1 pc)
Details[4]
Mass	1.447+0.075 −0.078 M☉
Radius	1.698+0.062 −0.057 R☉
Luminosity	4.71+0.38 −0.27 L☉
Surface gravity (log g)	4.139+0.041 −0.046 cgs
Temperature	6,530+160 −150 K
Metallicity [Fe/H]	0.068+0.070 −0.062 dex
Rotation	1.14[a] days
Rotational velocity (v sin i)	81.9±1.7 km/s
Age	1.77+0.88 −0.68 Gyr
Other designations
BD+16 3058, TIC 392476080, TYC 1521-208-1, GSC 01521-00208, 2MASS J16524472+1634478
Database references
SIMBAD	data
Exoplanet Archive	data

Characteristics

TOI-2109 is an F-type main-sequence star, a star moderately larger, hotter and more luminous than the Sun that is fusing hydrogen into helium at its core. It is 1.7 times larger than the Sun, comparable to Sirius A, 1.4 times more massive and nearly five times brighter. The effective temperature of its surface is 6,530 K (6,260 °C; 11,290 °F), which is 10% hotter than the Sun, whose temperature measures 5,772 K (5,499 °C; 9,930 °F). The age of TOI-2109 is uncertain, around 1.8 billion years. The rotation period of this star is 14% longer than Earth's day, about 1/25th that of the Sun.^[4]

Planetary system

Artist's impression of TOI-2109 b.

TOI-2109 hosts at least one exoplanet, which is named TOI-2109 b and was discovered in 2021 via the transit method.^[4]

TOI-2109 b is a hot Jupiter, with the shortest orbital period of its class. It completes an orbit in just 0.67 days (16 hours), being separated by only 0.01791 astronomical units (2,679,000 km) from its host star. This is the shortest period among hot Jupiters. The extreme proximity also means TOI-2109 b is strongly irradiated. The dayside temperature measures 3,630 K (3,360 °C; 6,070 °F), while the nightside is around 1,000 degrees cooler, at less than 2,500 K (2,230 °C; 4,040 °F). Only 55 Cancri e and KELT-9b have hotter dayside temperatures. This planet is around 30% larger than Jupiter and five times more massive. Its orbit is well-aligned to the star's axis.^[4]

In 2024, low-amplitude transit-timing variations were detected using the CHEOPS space telescope, which could be attributed to a yet unseen exoplanet. This putative planet should have an orbital period greater than 1.125 days and its other characteristics remain unconstrained.^[5]

The TOI-2109 planetary system^[5]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	5.02±0.75 MJ	0.01791±0.00065	0.67247414(28)	0	70.74±0.37°	1.347±0.047 RJ
c (unconfirmed)	—	—	>1.13; 1.57, 2.67, 88 or 117	—	—	—

Notes

1. Calculated using the p sin i of 1.05 days divided by the sine of the inclination, which is 67±6 degrees.