  An unprecedented number of exoplanets are being discovered by the Transiting
Exoplanet Survey Satellite (TESS). Determining the orbital parameters of these
exoplanets, and especially their mass and radius, will depend heavily upon the
measured physical characteristics of their host stars. We have cross-matched
spectroscopic, photometric, and astrometric data from GALAH Data Release 2, the
TESS Input Catalog and Gaia Data Release 2, to create a curated,
self-consistent catalog of physical and chemical properties for 47,285 stars.
Using these data we have derived isochrone masses and radii that are precise to
within 5\%. We have revised the parameters of three confirmed, and twelve
candidate, TESS planetary systems. These results cast doubt on whether
CTOI-20125677 is indeed a planetary system since the revised planetary radii
are now comparable to stellar sizes. Our GALAH-TESS catalog contains abundances
for up to 23 elements. We have specifically analysed the molar ratios for C/O,
Mg/Si, Fe/Si and Fe/Mg, to assist in determining the composition and structure
of planets with $R_p < 4R_\oplus$. From these ratios, 36% fall within 2 sigma
of the Sun/Earth values, suggesting that these stars may host rocky exoplanets
with geological compositions similar to planets found within our own Solar
system.
