Identification of late-type Class I stars using Gaia DR3 Apsis parameters

Abstract

Aims. We examined the Gaia DR3 GSP-Phot and GSP-Spec parameters of known K- and M-type stars of Class I luminosity to make a comparison with the parameters collected from the literature to assess their accuracy and their potential in setting stellar classifications of intrinsically bright late-types that have been unknown thus far. Gaia DR3 GSP-Phot and GSP-Spec parameters were generated by the astrophysical parameters inference software (Apsis). Methods. In the Gaia DR3 catalog, there are about 40,000 entries with Apsis parameters that are similar to those of known red supergiants (RSGs), good parallaxes, and infrared 2MASS and WISE data. In using parallactic distances, infrared photometry, and variability information, only 203 new entries were found with luminosities and temperatures similar to that of known RSGs and G-band amplitudes smaller than 0.5 mag. Their low-resolution BP/RP spectra were compared with an empirically built spectral library of BP/RP spectra of known bright late-type stars, including C-rich, S-type, O-rich asymptotic giant branch stars (AGBs) and RSGs, to obtain their spectral types. Results. Among them, 15 S-type stars were identified based on peculiar absorption features attributed to ZrO and LaO visible in their BP/RP spectra, along with 1 S/C star and 9 C-rich stars by their strong CN absorption bands. K- and M-types can be reproduced with an accuracy of two subtypes. In addition, 20 new RSGs have been confirmed, of which 6 have bolometric magnitudes that are brighter than those of the AGB limit: 2MASS J21015501+4517205, 2MASS J16291280-4956384, 2MASS J10192621-5818105, 2MASS J20230860+3651450, 2MASS J17084131−4026595, and 2MASS J16490055−4217328. The flag for C-rich stars of the Gaia DR3 LPV pipeline is erroneously positive for some RSGs and, thus, a visual inspection of the BP/RP spectra is mandatory.