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gaia data release 3 documentation

10.5 Cepheids

10.5.4 Processing steps

The processing includes the following steps that are in common for both Cepheid and RR Lyrae stars (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 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 Cepheid G-band light curves larger than 0.025 mag.

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

  1. 1.

    Cepheid multimode search;

  2. 2.

    Cepheid type identification;

  3. 3.

    type II Cepheid sub-classification in terms of BL Herculis, W Virginis, and RV Tauri classes;

  4. 4.

    classical Cepheid mode identification;

  5. 5.

    anomalous Cepheid mode identification;

  6. 6.

    Cepheid final classification and validation;

  7. 7.

    stellar parameters estimate: metallicity for fundamental mode Classical Cepheid variables with period shorter than about 6 days.

A detailed description of each step can be found in Clementini et al. (2016, 2019) and Ripepi et al. (2023).