  We collected near-infrared spectra of 65 cool stars with the NASA InfraRed
Telescope Facility (IRTF) and analyze them to calculate accurate metallicities
and stellar parameters. The sample of 55 M dwarfs and 10 K dwarfs includes 25
systems with confirmed planets and 27 systems with planet candidates identified
by the K2 and TESS missions. Three of the 25 confirmed planetary systems host
multiple confirmed planets and two of the 27 planet candidate systems host
multiple planet candidates. Using the new stellar parameters, we re-fit the K2
and TESS light curves to calculate updated planet properties. In general, our
updated stellar properties are more precise than those previously reported and
our updated planet properties agree well with those in the literature. Lastly,
we briefly examine the relationship between stellar mass, stellar metallicity,
and planetary system properties for targets in our sample and for previously
characterized planet-hosting low-mass stars. We provide our spectra, stellar
parameters, and new planetary fits to the community, expanding the sample
available with which to investigate correlations between stellar and planetary
properties for low-mass stars.
