  We present an alternative technique for measuring the precursor masses of
transient events in stars undergoing late stage stellar evolution. We use the
well-established techniques of stellar population modeling to age-date the
stars surrounding the site of the recent transient event in NGC 300 (NGC 300
OT2008-1). The surrounding stars must share a common turnoff mass with the
transient, since almost all stars form in stellar clusters that remain
physically associated for periods longer than the lifetime of the most massive
stars. We find that the precursor of NGC 300 OT2008-1 is surrounded by stars
that formed in a single burst between 8-13 Myr ago, with 70% confidence. The
transient was therefore likely to be due to a progenitor whose mass falls
between the main sequence turnoff mass (12 Msun) and the maximum stellar mass
(25 Msun) found for isochrones bounding this age range. We characterize the
general applicability of this technique in identifying precursor masses of
historic and future transients and supernovae (SNe), noting that it requires
neither precursor imaging nor sub-arcsecond accuracy in the position of the
transient. It is also based on the well-understood physics of the main
sequence, and thus may be a more reliable source of precursor masses than
fitting evolutionary tracks to precursor magnitudes. We speculate that if the
progenitor mass is close to 17 Msun, there may be a connection between optical
transients such as NGC 300 OT2008-1 and the missing type II-P SNe, known as the
"red supergiant problem."
