A Census of Red Supergiants in M31

Red supergiants are massive stars in their final stages of life, and as such they are important for understanding late stages of stellar evolution before catastrophically exploding as supernovae; however, getting precise masses for individual red supergiants remains difficult due to complexities in their upper atmosphere. These red supergiants reach luminosities so high that we can study them in galaxies outside our own Milky Way. Additionally, they show strong pulsation periods on time scales of months to years which directly relate to their radius and mass. The Zwicky Transient Facility (ZTF) is a large-scale sky survey which observes repeatedly, accumulating a few hundred observations over a time scale of a few years. I extract the ZTF data for a list of candidate targets of roughly 250 red supergiants from M31 to search for their pulsation periods. I use Gaussian Processes to approximate a curve over the data points for each target to conclude the periods for each. Gaussian Processes over more simple methods are required because red supergiants have a combination of periodic pulsations and random variability due to changes in the star’s atmosphere. My current results show pulsation periods between a few months to a year which correspond to red supergiants with masses around 12-15 solar masses. This study will provide a census of the most massive stars in M31 along with hopes of discovering red supergiants beyond 30 solar masses.