The Type II-P Supernova 2019mhm and Constraints on its Progenitor System

We present pre- and postexplosion observations of the Type II-P supernova (SN II-P) 2019mhm located in NGC 6753. Based on optical spectroscopy and photometry, we show that SN 2019mhm exhibits broad lines of hydrogen with a velocity of -8500 +/- 200 km s(-1) and a 111 +/- 2 day extended plateau in its luminosity, typical of the Type II-P subclass. We also fit its late-time bolometric light curve and infer that it initially produced a Ni-56 mass of 1.3 x 10(-2) +/- 5.5 x 10(-4) M (circle dot). Using imaging from the Wide Field Planetary Camera 2 on the Hubble Space Telescope obtained 19 yr before explosion, we aligned to a postexplosion Wide Field Camera 3 image and demonstrate that there is no detected counterpart to the SN to a limit of >24.53 mag in F814W, corresponding to an absolute magnitude limit of M (F814W) < -7.7 mag. Comparing to massive-star evolutionary tracks, we determine that the progenitor star had a maximum zero-age main-sequence mass M (circle dot), consistent with other SN II-P progenitor stars. SN 2019mhm can be added to the growing population of SNe II-P with both direct constraints on the brightness of their progenitor stars and well-observed SN properties.