An upper mass limit for the progenitor of the Type II-P supernova SN 1999gi

Masses and progenitor evolutionary states of Type II supernovae remain almo st unconstrained by direct observations. Only one robust observation of a p rogenitor (SN 1987A) and one plausible observation (SN 1993J) are available . Neither matched theoretical predictions, and in this Letter we report lim its on a third progenitor (SN 1999gi). The Hubble Space Telescope (HST) has imaged the site of the Type II-P supernova SN 1999gi with the Wide Field P lanetary Camera 2 (WFPC2) in two filters (F606W and F300W) prior to explosi on. The distance to the host galaxy (NGC 3184) of 7.9 Mpc means that the mo st luminous, massive stars are resolved as single objects in the archive im ages. The supernova occurred in a resolved, young OB association 2.3 kpc fr om the center of NGC 3184 with an association age of about 4 Myr. Follow-up images of SN 1999gi with WFPC2 taken 14 months after discovery determine t he precise position of the supernova on the preexplosion frames. An upper l imit of the absolute magnitude of the progenitor is estimated (M-v greater than or equal to -5.1). By comparison with stellar evolutionary tracks, thi s can be interpreted as a stellar mass, and we determine an upper mass limi t of 9(-2)(+3) M.. We discuss the possibility of determining the masses or mass limits for numerous nearby core-collapse supernovae using the HST arch ive enhanced by our current SNAP program.