A sub-Neptune planet around TOI-1695 discovered and characterized with SPIRou and TESS

TL;DR

This paper reports the discovery and characterization of a sub-Neptune exoplanet orbiting the M-dwarf star TOI-1695, using TESS photometry and SPIRou radial velocity data, providing insights into its composition and formation.

Contribution

First detection of a sub-Neptune planet around TOI-1695 with combined TESS and SPIRou data, including mass, radius, and atmospheric composition analysis.

Findings

Planet TOI-1695b has a mass of 5.5 ± 1.0 M⊕ and radius of 2.03 ± 0.18 R⊕.

The planet's density suggests a significant volatile component in its atmosphere.

The planet is at the border of the M-dwarf radius valley, informing formation models.

Abstract

TOI-1695 is a V-mag=13 M-dwarf star from the northern hemisphere at 45$\,$pc from the Sun, around which a 3.134-day periodic transit signal from a super-Earth candidate was identified in TESS photometry. With a transit depth of 1.3$\,$mmag, the radius of candidate TOI-1695.01 was estimated by the TESS pipeline to be 1.82$\,$R$_\oplus$ with an equilibrium temperature of $\sim 620\,$K. We successfully detect a reflex motion of the star and establish it is due to a planetary companion at an orbital period consistent with the photometric transit period thanks to a year-long radial-velocity monitoring of TOI-1695 by the SPIRou infrared spectropolarimeter. We use and compare different methods to reduce and analyse those data. We report a 5.5-$\sigma$ detection of the planetary signal, giving a mass of $5.5 \pm 1.0\,$M$_\oplus$ and a radius of $2.03 \pm 0.18\,$R$_\oplus$. We derive a mean equilibrium planet temperature of $590 \pm 90\,$K. The mean density of this small planet of $3.6 \pm 1.1\,$g$\,$cm$^{-3}$ is similar (1.7-$\sigma$ lower) than that of the Earth. It leads to a non-negligible fraction of volatiles in its atmosphere with $f_{H,He}=0.28^{+0.46}_{-0.23}$% or $f_\text{water}=23 \pm 12$%. TOI-1695$\,$b is a new sub-Neptune planet at the border of the M-dwarf radius valley that can help test formation scenarios for super-Earth/sub-Neptune-like planets.