Properties of Carbon-rich Asymptotic Giant Branch Stars in the LMC and the Milky Way

TL;DR

This study compares the properties of carbon-rich AGB stars in the LMC and the Milky Way using infrared data, modeling their spectral energy distributions to estimate distances and analyze their dust envelopes.

Contribution

It introduces a method to estimate distances of Galactic CAGB stars using SED fitting validated with LMC data, improving distance measurements for these stars.

Findings

CAGB stars in both galaxies have similar infrared properties.

LMC CAGB stars lack extremely thick dust envelopes.

SED-based distances are reliable for Galactic CAGB stars.

Abstract

We present a comparative study of carbon-rich asymptotic giant branch (CAGB) stars in the Large Magellanic Cloud (LMC; 7347 stars) and the Milky Way (7163 stars) using infrared color-magnitude diagrams, spectral energy distributions (SEDs), two-color diagrams, and variability data. Observed SEDs are compared with theoretical models to characterize the central stars and their circumstellar dust envelopes and to estimate distances. For the LMC, a set of best-fitting CAGB models is derived by fitting observed SEDs with radiative transfer models, utilizing the galaxy's well-established distance. For Galactic CAGB stars, where Gaia DR3 parallaxes are uncertain, we estimate distances by fitting observed SEDs with the CAGB models validated against LMC stars, and for Mira variables, from the period-magnitude relation calibrated with LMC Miras. A comparison of these approaches demonstrates that the SED-based distances are both reliable and practical for a large sample of Galactic CAGB stars. We find that CAGB stars in both galaxies show broadly similar infrared properties, although the LMC sample lacks stars with extremely thick dust envelopes.