TOI-1452 b: SPIRou and TESS Reveal a Super-Earth in a Temperate Orbit Transiting an M4 Dwarf

Abstract

Exploring the properties of exoplanets near or inside the radius valley provides insight on the transition from the rocky super-Earths to the larger, hydrogen-rich atmosphere mini-Neptunes. Here, we report the discovery of TOI-1452b, a transiting super-Earth (R-p = 1.67 +/- 0.07 R-circle times) in an 11.1 day temperate orbit (T-eq = 326 +/- 7 K) around the primary member (H = 10.0, T-eff = 3185 +/- 50 K) of a nearby visual-binary M dwarf. The transits were first detected by the Transiting Exoplanet Survey Satellite, then successfully isolated between the two 3.'' 2 companions with ground-based photometry from the Observatoire du Mont-Megantic and MuSCAT3. The planetary nature of TOI-1452b was established through high-precision velocimetry with the near-infrared SPTRou spectropolarimeter as part of the ongoing SPIRou Legacy Survey. The measured planetary mass (4.8 +/- 1.3 M-circle times) and inferred bulk density (5.6(-)(1.)(6)(+1.8) g cm(-3)) is suggestive of a rocky core surrounded by a volatile-rich envelope. More quantitatively, the mass and radius of TOI-1452b, combined with the stellar abundance of refractory elements (Fe, Mg, and Si) measured by SPTRou, is consistent with a core-mass fraction of 18% +/- 6% and a water-mass fraction of 22(-13)(+21)%. The water world candidate TOI-14521) is a prime target for future atmospheric characterization with JWST, featuring a transmission spectroscopy metric similar to other well-known temperate small planets such as LHS 1140b and K2-18 b. The system is located near Webb's northern continuous viewing zone, implying that is can be followed at almost any moment of the year

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