Searching for GEMS: TOI-7149~b an Inflated Giant Planet causing a 12% Transit of a Fully Convective M-dwarf

TL;DR

This paper reports the discovery of TOI-7149~b, a giant planet transiting a low-mass M-dwarf, with detailed characterization and implications for planet formation around such stars, using TESS data and ground-based follow-up.

Contribution

It presents the first detailed characterization of a giant planet transiting a very low-mass M-dwarf, expanding the known population of GEMS and analyzing their properties.

Findings

TOI-7149~b has a 12% transit depth, one of the deepest for main-sequence hosts.

GEMS hosts are likely high metallicity stars within 200 pc.

Giant planets around early and mid M-dwarfs have similar densities to those around FGK stars.

Abstract

We describe the discovery and characterization of TOI-7149~b, a 0.705 $\pm$ 0.075 $M_J$, 1.18 $\pm$ 0.045 $R_J$ gas giant on a $\sim 2.65$ day period orbit transiting an M4V star with a mass of 0.344 $\pm$ 0.030~\solmass{} and an effective temperature of 3363 $\pm$ 59 K. The planet was first discovered using NASA's TESS mission, which we confirmed using a combination of ground-based photometry, radial velocities, and speckle imaging. The planet has one of the deepest transits of all known main-sequence planet hosts at $\sim$ 12\% ($R_p/R_\star\sim 0.33$). Pushing the bounds of previous discoveries of \underline{G}iant \underline{E}xoplanets around \underline{M}-dwarf \underline{S}tars (GEMS), TOI-7149 is one of the lowest mass M-dwarfs to host a transiting giant planet. We compare the sample of transiting GEMS to stars within 200 pc with a Gaia colour magnitude diagram (CMD) and find that the GEMS hosts are likely to be high metallicity stars. We also analyze the sample of transiting giant planets using the non-parametric \texttt{MRExo} framework to compare the bulk density of warm Jupiters across stellar masses. We confirm our previous result that transiting Jupiters around early M-dwarfs have similar masses and densities to warm Jupiters around FGK stars, and extend this to mid M-dwarfs, thereby suggesting a potential commonality in their formation mechanisms.