Research
Introduction
My REU summer research project through CIERA (Northwestern University, 2026) was to analyze and constrain circumstellar dust properties around Red Supergiant (RSG) supernova progenitor candidates in M51 and M82 by determining the fraction of RSGs better explained by graphite-dominated versus silicate-dominated circumstellar dust models.
Results
In M51, the RSG sample consists of 3,360 stars, of which 63.9% were found to be silicate-dominated and 36.1% were graphite-dominated. Similarly, in M82, 68.0% of a sample of 303 RSGs were found to be silicate-dominated, while 32.0% were graphite-dominated. The prevalence of silicate-dominated sources in both galaxies is consistent with the oxygen-rich environments expected around RSGs, where C/O < 1 favors the formation of silicate dust. Silicate dust is therefore preferred in both galaxies.
However, the number of RSGs best represented by graphite models is somewhat unexpected, as graphite-dominated CSMs may indicate periods of dredge-up or unusual chemical evolution over their mass-loss histories, given that RSGs are generally expected to be silicate-dominated.
There is a difference of approximately 4 percentage points between silicate vs. graphite ratios in M51 and M82. Similar composition ratios between the two galaxies despite their diverse star-forming environments suggest that the dust chemistry of RSG CSM may be more strongly determined by stellar evolutionary processes than by differences in host-galaxy properties.