7.4.3 Calibration models

The SOS Cep&RRL processing uses tools such as: period-amplitude (PA) and period-luminosity (PL) relations in the G-band, as described in the documentation for the processing of RR Lyrae and Cepheid stars released in Gaia Data Release 1, (Clementini et al. 2016). For the Gaia Data Release 2 data processing (Clementini et al. 2018) we also use tools based on the GBP and GRP photometry, such as the period-luminosity in the RP-band and the period-Wesenheit (PW) relation in G, GRP. Furthermore, we implemented i) use of parallaxes according to the Astrometric Based Luminosity formulation, (i.e. working directly in parallax space; see, e.g., (Gaia Collaboration et al. 2017) and references therein) and applying different PL, PW relations depending on source position on sky (whether in the Large Magellanic Cloud, in the Small Magellanic Cloud or outside them); ii) calculation of metallicity ([Fe/H]) for the RR Lyrae stars and for δ Cepheid variables with period shorter than about 6 days from the Fourier parameters and, iii) calculation of interstellar absorption in the G-band for the RRab stars from a relation based on G-band peak-to-peak amplitude and period.