colloquium – Giulia De Somma: The classical Cepheids modelling in the Gaia Era

Classical Cepheids are the most used primary distance indicators to calibrate
the cosmic distance ladder and reliable stellar population tracers. These stars
have been adopted to probe galactic evolution and star formation, thanks to
their intrinsic variability and the link between pulsation properties and
evolutionary parameters. A theoretical approach to the study of these objects
is crucial to interpret observed behaviors and fully exploiting the accuracy of
observed oscillation characteristics in terms of stellar properties and distances.
By using the Stellingwerf hydrodynamical code, we recently provided detailed
homogeneous nonlinear Classical Cepheid pulsation models. We take into
account variations of chemical composition, mass-luminosity (ML) relation, and
efficiency of super-adiabatic convection.
The predicted pulsation observables included the instability strips, multi-filter
light curves, and the corresponding mean magnitudes and colors.
We used these quantities to derive metal-dependent period-luminosity-color
(PLC) and period-Wesenheit (PW) relations. The latter were applied to a
sample of Gaia Early Data Release 3 (DR3) Galactic Cepheids. The inferred
theoretical parallaxes were tested against Gaia astrometric results. By
combining this pulsational scenario with updated stellar evolution
predictions and using the BASTI code, we derived new and accurate metal-
dependent Period-Age and Period-Age-Color relations, which were applied to
the same sample of Galactic Cepheids in the Gaia DR3 to constrain their age
distribution. These results are all discussed in view of the incoming SPECTRUM
project that will represent the first attempt to systematically compute
nonlinear convective pulsation models along stellar evolutionary tracks.