Name/Affiliation: Benjamin Sargent (Rochester Institute of Technology)
Spitzer Space Telescope Infrared Spectrograph Studies of the Properties of Circumstellar Dust around Oxygen-Rich Asymptotic Giant Branch and Red Supergiant Stars
We analyze the dust emission features seen in Spitzer Space Telescope Infrared Spectrograph (IRS) spectra of Oxygen-rich (O-rich) asymptotic giant branch (AGB) and red supergiant (RSG) stars. The spectra come from the Spitzer Legacy program SAGE-Spectroscopy (PI: F. Kemper) and other archival Spitzer-IRS programs. The broad 10 and 20 micron emission features attributed to amorphous dust of silicate composition seen in the spectra show evidence for systematic differences in the centroid of both emission features between O-rich AGB and RSG populations. Radiative transfer modeling using the GRAMS grid of models of AGB and RSG stars suggests that the centroid differences are due to differences in dust properties. We show recent modeling using different dust opacities that we use to investigate differences in dust composition, size, shape, etc that might be responsible for these spectral differences. We explore how these differences may arise from differing physical conditions in the different circumstellar environments of RSG and O-rich AGB stars. BAS acknowledges funding from NASA ADAP grant NNX13AD54G.