Compare performance of GSP-Phot to Andy's SICK code when fitting only BP/RP.

Investigate fitting BP/RP alone, RVS alone, and BP/RP+RVS simultaneously with Andy's SICK code.

Is this a route to beat APSIS?

Where can BP/RP help to estimate abundances from RVS?

Where can RVS help to improve on BP/RP?

This project employs synthetic MARCS spectra.

GSP-Phot and SICK overall agree very nicely. No algorithm clearly outperforms the other.

logg: GSP-Phot is slightly better than SICK. SICK may suffer from some convergence problems (red dots below dwarfs).

[Fe/H]: SICK is slightly better than GSP-Phot. GSP-Phot appears to systematically underestimate [Fe/H] by ~1dex for some stars. These problematic stars are fainter than G~15, i.e., SICK estimates [Fe/H] more robustly at lower S/N than GSP-Phot.

2000 synthetic MARCS spectra in Gaia BP/RP.

Mostly Main-Sequence dwarfs but also some giants.

Teff from 4000K to 8000K.

Test spectra created by GOG. (Not by our own forward models!)

Posterior distributions mostly well behaved for BP/RP, i.e., fast convergence, unimodal.

Even in simple case the posteriors cannot be well approximated by a Gaussian.

Rare examples with multimodal posterior.

Compare initial guesses of GSP-Phot and SICK. (Possibly SVM fails for noisy data, which may explain why SICK estimates [Fe/H] better at faint magnitudes.)