10.11.4 Processing steps

The processing of the SOS Cep&RRL pipeline includes the following steps that are in common to both RR Lyrae stars and Cepheids (see figure 1 in Clementini et al. 2019):

1. 1.

   derivation of period and harmonics (amplitudes and phases) by non-linear Fourier analysis;

2. 2.

   measurement of the light and radial velocity curve parameters (intensity-averaged mean magnitudes, mean radial velocity, amplitudes, epochs of maximum light for the photometry, epoch of minimun for the radial velocity, etc.);

3. 3.

   consistency check of the periods derived from the 3 photometric bands ($G$, $G_{\mathrm{BP}}$, and $G_{\mathrm{RP}}$);

4. 4.

   search for secondary periodicities, performed only for sources with $>40$ transits in the $G$ band and with scatter of the best-fit model of the RR Lyrae $G$-band light curves larger than 0.05 mag.

The following additional steps are then applied to sources confirmed as RR Lyrae stars (see figure 2 in Clementini et al. 2019):

1. 1.

   identification of double-mode RR Lyrae stars;

2. 2.

   non-linear modelling of double-mode RR Lyrae stars;

3. 3.

   pulsation mode identification;

4. 4.

   RR Lyrae classification and validation;

5. 5.

   stellar parameters derivation: metallicity;

6. 6.

   stellar parameters derivation: absorption in the $G$-band for RRab stars (g_absorption).

Examples of $G$, $G_{\mathrm{BP}}$, $G_{\mathrm{RP}}$ light curves and radial velocity curves for first overtone (RRc), double-mode (RRd) and fundamental mode (RRab) RR Lyrae stars confirmed and fully characterized by the SOS Cep&RRL pipeline are shown in Figure 10.28.