TOI-1846 b: A super-Earth in the radius valley orbiting a nearby M dwarf

We present the discovery and validation of a super-Earth planet orbiting the M dwarf star TOI-1846 (TIC 198385543). The host star (Kmag = 9.6) is located 47 pc away and has a radius of R⋆ = 0.41 ± 0.01$\rm \, R_\odot$, a mass of M⋆ = 0.40 ± 0.02$\rm \, M_\odot$ and an effective temperature of Teff = 3568 ± 44K. Our analyses are based on joint modelling of TESS photometry and ground-based multi-color photometric data. We also use high-resolution imaging and archival images, as well as statistical validation techniques to support the planetary system nature. We find that TOI-1846 b is a super-Earth sized planet with radius of Rp = 1.79 ± 0.07$\rm \, R_\oplus$ and a predicted mass of $M_p = 4.4^{+1.6}_{-1.0}$$\rm \, M_\oplus$ (from the Chen & Kipping relation) on a 3.9 d orbit, with an equilibrium temperature of Teq = 589 ± 20K (assuming a null Bond Albedo) and an incident flux of Sp = 17.6 ± 2.0 S⊕. Based on the two RV measurements obtained with the TRES spectrograph and high-resolution imaging, a non-planetary transiting companion is excluded. With a radius of ≈1.8$\rm \, R_\oplus$, TOI-1846 b is within the sparsely populated radius range around 2$\rm \, R_\oplus$ known as the radius gap (or radius valley). This discovery can contribute to refining the precise location of the radius valley for small planets orbiting bright M dwarfs, thereby enhancing our understanding of planetary formation and evolution processes.