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gaia data release 3 documentation

10.11 RR Lyrae stars

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, GBP, and GRP);

  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, GBP, GRP 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.

Figure 10.28: Examples of G, GBP, GRP light curves (upper three curves in each panel) and radial velocity curve (lower curve) for confirmed first overtone (RRc), double-mode (RRd) and fundamental mode (RRab) RR Lyrae stars. Units on the Y axis are mag for the light curves and km s-1 for the radial velocity curves. The data are folded according to the periods derived by the SOS Cep&RRL pipeline and plotted over two cycles. A few outliers not removed by the outlier removal operators are still present in some of the GBP and GRP curves, however they do not affect the light curve models and mean GBP, GRP magnitudes computed by the SOS Cep&RRL pipeline.