Speaker
Description
The third early Gaia data release (EDR3) has improved the accuracy of the astrometric parame-
ters of numerous long-period variables (LPVs) stars. Many of these stars are on the Asymptotic
Giant Branch (AGB), showing either a C-rich or O-rich envelope and are characterised by high
luminosity, changing surface composition, and intense mass loss, that make them very useful for
stellar studies. In a previous investigation we used Gaia DR2 astrometry to derive the luminos-
ity function, kinematic properties and stellar population membership of a flux limited sample of
carbon stars in the solar neighbourhood of different spectral types. Here, we extend this initial
study to more ample and recent surveys of Galactic carbon stars and related stars by adopting the
more accurate EDR3 astrometry measurements. Thanks to a much larger statistics, we confirm
that N- and SC-type carbon stars share a very similar luminosity function, while the J-type stars
show luminosities (Mbol ) fainter by half a magnitude in average. The carbon stars of R-hot type
show luminosities all along the RGB, which favours the hypothesis of an external origin for their
carbon enhancement. Moreover, a significant fraction of the R-hot stars have kinematics proper-
ties compatible with the thick disk population, in contrast with that of N-, SC-type stars which
would belong mostly to the thin disk. We also derive the luminosity function of a large num-
ber of Galactic extrinsic and intrinsic (O-rich) S-stars and show that the latter have luminosities
typically higher than the predicted onset of the third dredge-up (TDU) during the AGB for solar
metallicity. This result is consistent with these stars being genuine thermal pulsing (TP) AGB
stars. On the other hand, using the so-called Gaia-2MASS diagram we show that the overwhelm-
ing 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 AGB carbon
stars candidates, identified thanks to their 2MASS photometry, their Gaia astrometry, and their
location in the Gaia-2MASS diagram.
| Session | Stellar observations (photometry and spectrometry) |
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