A homogeneous view of asymptotic giant branch carbon stars as seen by Gaia

Context. Carbon stars on the asymptotic giant branch are major contributors to the dust enrichment of galaxies, with gas mass-loss rate values up to Ṁ ≍ 10⁻⁴ M_⊙ yr⁻¹. They represent the final evolutionary stage of low- and intermediate-mass stars, during which recurrent dredge-up episodes enrich their atmospheres with carbon and trigger the formation of dust. Through their intense winds, they inject large amounts of newly formed carbonaceous dust into the interstellar medium, playing a central role in the chemical evolution of galaxies. Their stellar and dust properties have been studied for decades, with a particular focus on the carbon stars in the Magellanic Clouds (MCs). Aims. Our aim is to homogeneously analyse the Gaia DR3 Golden Sample of Carbon Stars through the spectral energy distribution (SED) fitting. Our focus is on sources belonging to the Milky Way (MW) and the MCs. Methods. Our dataset consists of 14 747 stars with complete multi-band photometry from Gaia, 2MASS, and WISE, combined with recent distance and extinction estimates. For a subsample of Mira variables made of 2494 stars, we also modelled multi-band light curves to obtain accurate mean magnitudes. Stellar and circumstellar properties were derived by fitting the observations with a large grid of synthetic models computed with the DUSTY radiative transfer code, using COMARCS model atmospheres as input. For each target, we determined stellar and dust parameters such as the effective temperature, optical depth, and gas mass-loss rate. Results. The resulting distributions reveal typical effective temperatures of around 3150 K. Mass-loss rates range from 10⁻¹¹ to 10⁻⁴ M_⊙ yr⁻¹. The average dust temperature at the inner bound of the dust shell is about T_d = 1000 K. We also observe a correlation between photometric variability amplitude and mass-loss rate. Conclusions. This homogeneous framework provides a unified view of carbon stars across environments spanning a wide range of metallicities, supported by strong statistical coverage. Our results show that some of the physical properties of carbon stars exhibit a dependence on the galactic environment. However, these dependences do not necessarily reflect intrinsic metallicity effects, but are influenced by differences in luminosity distributions and by the selection biases affecting the available samples. The use of Gaia and WISE introduces combined selection effects that are significant, limiting the detection of both the most dust-enshrouded objects and the less luminous sources in the Magellanic Clouds. While this limits the completeness of the comparison, the observed trends remain statistically robust within the selected samples.