7.4.4 Processing steps

The processing includes the following steps common to both RR Lyrae and Cepheid stars (see Fig. 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 light curve parameters (mean magnitudes, amplitudes, epochs of maximum light, etc.),

3. 3.

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

4. 4.

   Search for secondary periodicities.

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

1. 1.

   RR Lyrae Double-mode search,

2. 2.

   Non-linear double-mode modelling,

3. 3.

   Amplitude ratios,

4. 4.

   Mode identification,

5. 5.

   RR Lyrae Classification and validation,

6. 6.

   Stellar parameters derivation: metallicity,

7. 7.

   Stellar parameters derivation: absorption in the $G$-band for RRab stars.

and the following additional steps applied to sources confirmed as Cepheid variables (see Fig. 3 in Clementini et al. 2019):

1. 1.

   Cepheid Multimode search,

2. 2.

   Cepheid Type identification,

3. 3.

   Type II Cepheid Subclassification,

4. 4.

   $\delta$ Cepheid Mode identification,

5. 5.

   ACEP Mode identification,

6. 6.

   Cepheid Classification and validation,

7. 7.

   Stellar parameters derivation: metallicity for $\delta$ Cepheid variables with period shorter than about 6 days.