Employ high-resolution spectra from X-shooter archive to investigate how the Gaia spectra will look like.

Investigate GSP-Phot performance on X-shooter spectra.

Gaia RVS spectra and corresponding segments of x-shooter spectra look very similar. Ca-Triplet lines are easily identified and other prominent lines are also in obvious correspondence.

x-shooter spectra contain telluric bands around 760nm and 950nm. In fact, BP/RP shows prominent dips there, which are NOT reflected by space-based instrument models. That must be a problem when modelling those spectra with GSP-Phot.

Paula compiled mean parameters for all stars from Pastel. (These are no “true” values but mean literature values.)

Paula's data contains a lot of giants. GSP-Phot lacks giants in its training data, i.e., it is unlikely to perform well on giants (c.f. Challenge 4).

GSP-Phot performs very poorly on x-shooter spectra: Teff is loosely related for some stars, but logg looks rather random and GSP-Phot tends to assign too low [Fe/H].

x-shooter spectra are ground-based spectra, including telluric features, that are not part of the Gaia spectra.

Lack of giants in GSP-Phot training data.

x-shooter spectra were processed with GOG version 14, whereas GSP-Phot training data was processed with GOG version 8.