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

We describe the discovery and characterization of TOI-7149 b, a 0.705 ± 0.075 M J , 1.18 ± 0.045 R J gas giant on a ∼2.65 days period orbit transiting an M4V star with a mass of 0.344 ± 0.030 M ⊙ and an effective temperature of 3363 ± 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 ∼12% ( R p / R ⋆ ∼ 0.33). Pushing the bounds of previous discoveries of giant exoplanets around M-dwarf stars (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 color–magnitude diagram and find that the GEMS hosts are likely to be high metallicity stars. We also analyze the sample of transiting giant planets using the nonparametric 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.