  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.
