Pulsating variable stars

People involved at OAB: Bellazzini, Cacciari, Clementini, Contreras, Federici, Fiorentino, Greco, Fusi Pecci, Tosi.

Pulsating variable stars are fundamental tools to set the astronomical distance scale, and to sample different stellar populations in galaxies. In particular, the RR Lyrae stars are excellent tracers of the oldest stellar population in galaxies. They bear witness to the epoch of galaxy formation, and their pulsation properties (periods, period-amplitude relations, etc.) can provide fundamental insights on the processes that lead to the assembling of galaxies. Also, they are the primary Population II distance indicators in the LG, through the RR Lyrae luminosity-metallicity relation, (M $_V \rm (RR) - [Fe/H])$ and the $P$-$L$ relation in the $K$ band. On the other hand, Cepheids are among the brightest stellar candles. Their $P$-$L$ relation remains the most important of the primary distance indicators for nearby galaxies hosting a young stellar population, up to distances of 30 Mpc.

The role of pulsating variable stars in establishing the astronomical distance scale has been a major field of study at the INAF-OAB since 1984. A large number of new projects (see e.g. Clementini 2007a, Clementini et al. 2007b) were started in more recent years, in collaboration with scientists of the INAF-Padova, Napoli and Merate Observatories, as well as with scientists of several International Institutes, to map out the variable star content in galaxies of different morphological type and to exploit their potential as distance indicators and stellar population tracers.