Pradosh Das

Deriving Stellar Parameters and abundances: Employing “The Cannon” to Bridge GALAH-DR4 to GAIA-RVS Spectra

The enormous spectroscopic datasets from current astronomical surveys provide an unprecedented opportunity to explore the stellar populations of the Milky Way and its surroundings. The largest surveys range from several million stars (e.g., LAMOST) to the roughly quarter-billion stars observed with Gaia XP spectra. These survey data are generally at low or moderate spectroscopic resolutions, yet the “gold standard” for determining stellar parameters and elemental abundances remains high-resolution spectroscopic data. We have used The Cannon, a largely Australian-developed, data-driven method to transfer labels from high-resolution reference data to lower-resolution data, specifically applying stellar parameters and abundances derived from GALAH data (GALAH iDR4) to Gaia RVS spectra (Gaia DR3). We trained our data model on ~14000 selected targets common to both surveys, utilising the stellar labels from GALAH. With this model, we are able to consistently predict stellar parameters such as Teff, log g, [Fe/H], and abundances of several alpha elements for over 800,000 Gaia RVS spectra. Using stars from several open and globular clusters present in the Gaia RVS catalogue, we have validated our metallicity estimates. Finally, for a subset of this sample with predicted log g < 3.5 (i.e., giants) we are able to measure the abundances of several neutron-capture elements, illustrating the exciting potential of this method for reliably determining stellar parameters and abundances from medium-resolution Gaia RVS spectra – a dataset which, by the end of the Gaia mission, is expected to include over 30 million stars.