Tests of simulated Gaia BP/RP spectra with LDS (Low Dispersion Spectroscopy) photographic sky surveys

The LDS (Low Dispersion Spectroscopy) performed in various extended sky surveys with optical telescopes using objective prism and photographic plates offers an interesting opportunity to test simulated low-dispersion spectra for the Gaia BP/RP photometers and to compare them with real data, especially for objects with strong emission lines. We present a review of astrophysics with LDS performed in the past, as well as an overview of existing extended sky surveys (with photographic plates) providing LDS data. Some of them provide almost complete coverage of the northern or southern hemisphere (e.g. the Northern and Southern Mt Wilson - Michigan Hα surveys or the German La Paz Bolivia Southern Spectral Sky Survey). We show examples of these data and discuss a comparison of existing LDS plate data with expected/simulated Gaia BP/RP data. We show examples of real data for objects with very strong and wide emission features confirming that such features will be detectable with Gaia BP/RP. We also discuss the importance of Gaia RP/BP low-dispersion spectroscopy for astrophysical studies.