The Andromeda and Triangulum galaxies (or M31/M33) are the nearest large spiral galaxies to our Milky Way. A third of M31 and all of M33 were observed from the UV to the infrared with Hubble by the Panchromatic Hubble Andromeda and Triangulum (PHAT) Treasury programs (PI Dalcanton).
I am PI of three followup Hubble program aimed at studying the carbon stars in both galaxies.
GO-12862: A pilot program to test the efficacy of the medium band infrared filters (F127M, F139M, and F153M) in distinguishing carbon and oxygen-rich stars. We found a conspicuous lack of carbon stars in the field observed. The results are summarized in Boyer et al. (2013).
GO-14072: Given the success of the pilot program, we observed 20 fields across the PHAT coverage in M31 using the infrared medium-bands. We found a dramatic decrease in carbon star formation towards the bulge that cannot currently be explained by models. See Boyer et al. (2019)
GO-15932: In Cycle 27, our program to image additional fields in both M31 and M33 with the infrared filters was approved. Observations are expected in 2020.