TOI-4342

TOI-4342 is a red dwarf star in the constellation Octans located 201 light-years from Earth. It hosts two transiting exoplanets. Both planets are considered to be good targets for transmission spectroscopy measurements for determination of atmospheric composition.^[2]

TOI-4342

Observation data Epoch J2000.0      Equinox J2000.0
Constellation	Octans
Right ascension	21h 37m 32.864s[1]
Declination	−77° 58′ 43.51″[1]
Apparent magnitude (V)	12.669±0.057[2]
Characteristics
Evolutionary stage	main sequence
Spectral type	M0V[2]
Apparent magnitude (B)	14.055±0.011[2]
Apparent magnitude (J)	9.832±0.024[3]
Apparent magnitude (H)	9.179±0.024[3]
Apparent magnitude (K)	9.018±0.021[3]
Variable type	planetary transit
Astrometry
Radial velocity (Rv)	−4.43±0.36[1] km/s
Proper motion (μ)	RA: 120.333±0.019 mas/yr[1] Dec.: −91.503±0.018 mas/yr[1]
Parallax (π)	16.2487±0.0184 mas[1]
Distance	200.7 ± 0.2 ly (61.54 ± 0.07 pc)
Details[2]
Mass	0.6296±0.0086 M☉
Radius	0.599±0.013 R☉
Luminosity	0.0746±0.0053 L☉
Surface gravity (log g)	4.6878+0.0086 −0.0096 cgs
Temperature	3901±69 K
Metallicity [Fe/H]	0.187[4] dex
Other designations
Gaia DR2 6355915466180482944, Gaia DR3 6355915466181029376, TOI-4342, TIC 354944123, 2MASS J21373286−7758435, GALAH 171003003101372[5]
Database references
SIMBAD	data
Exoplanet Archive	data

Stellar characteristics

TOI-4342 is an early red dwarf with an effective temperature of 3901±69 K, corresponding to the spectral class M0V.^[2] It is a single star with stellar companions ruled out by sky surveys, speckle imaging and the radial velocity method.^[2]

Planetary system

The star hosts two planets discovered by the transit method. They were initially observed in TESS data from Sector 13 (June and July 2019) and Sector 27 (July 2020) and were validated with ground based observations with LCO telescope network during 2021, with a study published in 2023. The planets are orbiting close to a 2:1 mean-motion resonance.^[2]

The TOI-4342 planetary system^[2][a]

Companion (in order from star)	Mass	Semimajor axis (AU)	Orbital period (days)	Eccentricity	Inclination	Radius
b	7.83+0.93 −0.88 M🜨	0.05251+0.00011 −0.00011	5.5382498+0.0000057 −0.0000058	~0	89.13+0.15 −0.13°	2.266+0.038 −0.038 R🜨
c	8.53+0.90 −0.94 M🜨	0.08140+0.00017 −0.00017	10.688716+0.000015 −0.000015	~0	89.63+0.12 −0.12°	2.820+0.024 −0.025 R🜨

Both planets are sub-Neptunes, similar in size, expected to have atmospheres with a significant fraction of hydrogen and helium. Based on the calculated insolation, the planets are expected to have equilibrium temperatures of 633.6+6.2
−6.3 K and 508.9+5.0
−5.0 K respectively.^[2]

As of January 2025^[update], the planets' masses have not yet been directly measured, though their masses estimated based on the empirical mass–radius relationship were noted in the discovery paper to fall above the limits of detection for the radial velocity method.^[2]

Due to orbiting within 5% of the 2:1 mean-motion resonance, the system is expected to show transit-timing variations due to mutual perturbations. Observation of the amplitudes of this perturbation could additionally help constrain planet masses. However, the limited observations available by the time of the discovery paper were only adequate to rule out deviations by more than 5 min from linear ephemerides.^[2] The observed low value of perturbation also confirms a low orbital eccentricity for the planets.^[2]

See also

• TOI-270 – another M-type main sequence star with two sub-Neptunes

Notes

1. Masses are not directly measured, they are estimated from an empirical mass-radius relationship.