Modelling TP-AGB Stars in M31 with PHAT Data

The thermally pulsing asymptotic giant branch (TP-AGB) phase is still the most uncertain phase among the main evolutionary phases of single stars, due to complicated processes involved, such as third dredge-up (3DU) and mass loss. These processes significantly affect the lifetime, luminosity, colors and chemical yields of TP-AGB stars. With HST high resolution imaging data from the Panchromatic Hubble Andromeda Treasury (PHAT) survey, TP-AGB stars are resolved in M31. This enables us to study the color-magnitude diagram and luminosity functions of TP-AGBs of different metallicity and mass within different environments (from the bulge to the disk) of M31. Therefore, PHAT data provides strong constraints for TP-AGB models. In this preliminary work, we calibrate TP-AGB evolutionary tracks with PHAT data using stellar population synthesis approach. By adjusting the parameters regulating the third dredge-up occurrence and efficiency as well as the prescription of mass-loss in the model, we are able to satisfactorily reproduce the observed luminosity function (F160W) and color-magnitude diagram (F110W-F160W vs. F160W)....