Characterisation of Galactic carbon stars and related stars from Gaia-EDR3

TL;DR

This study uses Gaia-EDR3 data to analyze the properties, luminosity functions, and kinematics of Galactic carbon stars and related types, revealing their origins, evolutionary status, and identifying new candidates.

Contribution

It provides a comprehensive characterization of various Galactic carbon star types using Gaia-EDR3 data, including new candidate identifications and insights into their origins and evolution.

Findings

N- and SC-type stars share similar luminosity functions.

J-type stars are generally fainter by half a magnitude.

Most extrinsic and intrinsic S stars are consistent with thermally pulsing AGB stars.

Abstract

We extend here a previous investigation on the characteristics of Galactic carbon stars using more accurate EDR3 astrometry measurements. Based on a much larger statistics, we confirm that N- and SC-type carbon stars share a very similar luminosity function, while the luminosities of J-type stars (Mbol) are fainter by half a magnitude on average. R-hot type carbon stars have luminosities throughout the RGB, which favours the hypothesis of an external origin for their carbon enhancement. Moreover, the kinematic properties of a significant fraction of the R-hot stars are compatible with the thick-disc population, in contrast with that of N- and SC-type stars, which would belong mostly to the thin disk. We also derive the luminosity function of a large number of Galactic extrinsic and intrinsic (O-rich) S stars and show that the luminosities of the latter are typically higher than the predicted onset of the third dredge-up during the AGB for solar metallicity. This result is consistent with these stars being genuine thermally pulsing AGB stars. On the other hand, using the so-called Gaia-2MASS diagram, we show that the overwhelming majority of the carbon stars identified in the LAMOST survey as AGB stars are probably R-hot and/or CH-type stars. Finally, we report the identification of 2660 new carbon stars candidates that we identified through their 2MASS photometry, their Gaia astrometry, and their location in the Gaia-2MASS diagram.