Deriving chemo-physical parameters of M-type giants from their Gaia RVS spectra: Update to the Gaia GSP-Spec pipeline

The Gaia mission provides powerful astrometric precision, spectro-photometric observations in the
visible, and medium resolution (R~11500) spectroscopy (by the Radial Velocity Spectrograph, RVS)
around the infrared calcium triplet. The RVS spectra allows for the derivation of stellar radial
velocities and, through the analysis of the GSP-Spec module, the estimation of effective temperatures
(Teff), surface gravities (log g), and chemical abundances ([M/H], [α/Fe], and [X/Fe] for up to 15
chemical elements). The Gaia DR3 GSP-Spec all-sky catalogue provided these parameters for ~5.6
millions stars, using their mean RVS spectra. Furthermore, the Gaia DR4 will include all epoch RVS
spectra for these stars (and more).
Access to these parameters for a large sample of Mira pulsating stars, as bright intermediate-age
standard candles, would allow for a detailed chemical and dynamical study of the Galaxy's
intermediate-age stellar populations far beyond the solar neighborhood, in addition to studies of the
variability of Mira stars through their epoch spectra. However, due to the cold temperatures (Teff ≲
3500 K) and weak surface gravities (log g 0.5 dex) in these stars' atmospheres, their spectra show≲
no continuum and are difficult to model. Thus, reliably parametrizing these stars remains a challenge.
We are working on improving GSP-Spec's performance for the cold giants domain, with the goal of
reliably characterizing RVS epoch spectra of Mira variables, opening new paths for a large scale
chemical cartography of the Milky Way and its satellites. In this talk, the results of this analysis with
public RVS mean spectra of M-type giants (and reference Teff, log g, and [M/H] values from the
literature) will be presented.