The Mass Loss Return from Evolved Stars to the Large Magellanic Cloud I. Empirical Relations for Excess Emission at 8 and 24 µm

To measure the mass loss from dusty oxygen-rich (O-rich) evolved stars in the Large Magellanic Cloud (LMC), we have constructed a grid of models of spherically-symmetric dust shells around stars with constant mass-loss rates us-ing 2Dust. These models will constitute the O-rich model part of the “Grid of Red supergiant and Asymptotic giant branch star ModelS ” (GRAMS). This model grid explores 4 parameters – stellar effective temperature from 2100 K– 4700 K; luminosity from 103–106L; dust shell inner radii of 3, 7, 11, and 15Rstar; and 10.0µm optical depth from 10−4 to 26. From an initial grid of ∼ 1200 2Dust models, we create a larger grid of ∼ 69 000 models by scaling to cover the lumi-nosity range required by the data. These models are offered to the public on a website. The matching in color-magnitude diagrams and color-color diagrams to observed O-rich asymptotic giant branch (AGB) and red supergiant (RSG) can-didate stars from the SAGE and SAGE-Spec LMC samples and a small sample of OH/IR stars is generally very good. The extreme AGB star candidates from SAGE are more consistent with carbon-rich (C-rich) than O-rich dust compo-sition. Our model grid suggests lower limits to the mid-infrared colors of the dustiest AGB stars for which the chemistry could be O-rich. Finally, the fitting of GRAMS models to SEDs of sources fit by other studies provides additional verification of our grid and anticipates future, more expansive efforts