Constraining the thermally pulsing asymptotic giant branch phase with resolved stellar populations in the Small Magellanic Cloud

Abstract

The thermally-pulsing asymptotic giant branch (TP-AGB) experienced by low-\nand intermediate-mass stars is one of the most uncertain phases of stellar\nevolution and the models need to be calibrated with the aid of observations. To\nthis purpose, we couple high-quality observations of resolved stars in the\nSmall Magellanic Cloud (SMC) with detailed stellar population synthesis\nsimulations computed with the TRILEGAL code. The strength of our approach\nrelies on the detailed spatially-resolved star formation history of the SMC,\nderived from the deep near-infrared photometry of the VISTA survey of the\nMagellanic Clouds, as well as on the capability to quickly and accurately\nexplore a wide variety of parameters and effects with the COLIBRI code for the\nTP-AGB evolution. Adopting a well-characterized set of observations -- star\ncounts and luminosity functions -- we set up a calibration cycle along which we\niteratively change a few key parameters of the TP-AGB models until we\neventually reach a good fit to the observations. Our work leads to identify two\nbest-fitting models that mainly differ in the efficiencies of the third\ndredge-up and mass loss in TP-AGB stars with initial masses larger than about 3\nM$_{\\odot}$. On the basis of these calibrated models we provide a full\ncharacterization of the TP-AGB stellar population in the SMC in terms of\nstellar parameters (initial masses, C/O ratios, carbon excess, mass-loss\nrates). Extensive tables of isochrones including these improved models are\npublicly available.\n