The NGC 300 Transient: An Alternative Method For Measuring Progenitor Masses

TL;DR

This paper introduces a new method using stellar population modeling to estimate the progenitor masses of stellar transients, avoiding the need for precursor imaging and relying on well-understood main sequence physics.

Contribution

The authors develop and demonstrate an alternative technique for determining progenitor star masses of transients based on surrounding stellar populations, applicable without precise transient positioning.

Findings

Progenitor of NGC 300 OT2008-1 likely had a mass between 12 and 25 solar masses.

The surrounding stars formed in a burst 8-13 million years ago with 70% confidence.

The method can be applied to historic and future transients without precursor imaging.

Abstract

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."