M31 Long Period Variables : Photometry

We report the results, including near-infrared photometry of almost 2000 variables, and light curves in the i band. The period-luminosity relation suggests that most of the variables are asymptotic giant branch stars, and their luminosity function can be understood in terms of mass-loss rates, which increase with increasing luminosity on the giant branch, and star formation rates, which were a few times higher a billion years ago in M31 than they are today.

We see some supergiant long-period variables, but somewhat fewer than expected based on their frequency in M33, and confined to the ring of star formation in M31 seen in the IRAS and 2MASS surveys.