The TESS mission detected a companion orbiting TIC 71268730, categorized it as a planet candidate, and designated the system TOI-5375. Our follow-up analysis using radial velocity data from the Habitable-zone Planet Finder (HPF), photometric data from Red Buttes Observatory (RBO), and speckle imaging with NN-EXPLORE Exoplanet Stellar Speckle Imager (NESSI) determined that the companion is a very low mass star (VLMS) near the hydrogen-burning mass limit with a mass of 0.080$\pm{ 0.002} M_{ \Sun}$ ($83.81\pm{ 2.10} M_{ J}$), a radius of 0.1114$^{ +0.0048}_{ -0.0050} R_{ \Sun}$ (1.0841$^{ 0.0467}_{ 0.0487} R_{ J}$), and brightness temperature of $2600\pm{ 70}$ K. This object orbits with a period of 1.721553$\pm{ 0.000001}$ days around an early M dwarf star ($0.62\pm{ 0.016}M_{ \Sun}$). TESS photometry shows regular variations in the host star's TESS light curve, which we interpreted as activity-induced variation of $\sim$2\%, and used this variability to measure the host star's stellar rotation period of 1.9716$^{ +0.0080}_{ -0.0083}$ days. The TOI-5375 system provides tight constraints on stellar models of low-mass stars at the hydrogen-burning limit and adds to the population in this important region.
Categories: astro-ph.SR astro-ph.EP