The Large-scale surveys as bridges between spectroscopy and photometry meeting belongs to the "RRLyr and Cepheid stars" series. Previous editions were held in Visegrad (Hungary) in 2015, in Niepolomice (Poland) in 2017, in Cloudcroft (USA) in 2019. This fourth event was scheduled for 2021, but the pandemic forced its postponement by one year. The community had spoken in favour of a meeting to be held mainly in presence in the La Palma island.

Panoramic view of the Roque de Los Muchachos observatory [Credit M. Pedani]

The purpose of the series is to bring together the specialists of stellar pulsations in the classical instability strip (i.e., variables like δ Scuti, SX Phe, RR Lyr, Cepheids, Long-Period and Mira variables). These pulsating stars are used both as distance indicators and as laboratories for the study of stellar interiors. Large photometric surveys such as OGLE and MACHO have strongly contributed to the massive detection of RR Lyr in different stellar systems. They improved the Period-Luminosity relations and enhanced the variety of the physical properties supplied by the classical Petersen diagrams of radial modes. The surveys by CoRoT, Kepler, TESS satellites made it possible to detect non-radial modes, unveiling an unexpected mode mixture. RR Lyr and Cepheids are thus entering the domain of the ensemble asteroseismology, opened by δ Sct and LPV variables. Other more complex phenomena such as the Blazhko effect and cycle-to-cycle variations are challenging our knowledge of the stellar atmospheres. The all-sky survey made by Gaia puts all our variables at the right place in the Galaxy, largely improving their use as distance ladders and the DR3 will disclose the huge treasure of the photometric time series. Not only this, the Vera Rubin Observatory will be a further large-scale photometric facility for the study of pulsating variables.

All these aspects will be revisited in the light of recent observational data. However, the new purpose of the La Palma meeting is to discuss how spectroscopy contributes to the study of pulsating variables. Spectroscopic surveys (APOGEE, S5 , RAVE, ...) produced homogeneous sets of catalogs and databases very helpful to define the environments where our variables are located. On the other hand, high-resolution spectroscopy is essential to investigate the projection factor to solve the H0 tension, to check the differences between the behaviours of photosphere and chromosphere induced by pulsations, to discover low-metallicity stars, and to certify cycle-to-cycle variations.

The Observatorio del Roque de Los Muchachos (ORM) in the La Palma island hosts the Telescopio Nazionale Galileo (TNG), equipped with the HARPS-N and GIANO-B instruments, well suited to perform high-resolution spectroscopy. In the next months the WEAVE multifiber spectrograph mounted at the William Herschel Telescope (WHT), also at the ORM, will be able to contribute to large-scale surveys. Not only the TNG and the WHT, but the whole battery of the ORM telescopes (Gran Telescopio Canarias, Nordic Optical Telescope, Mercator, …) are suitable to study pulsating variables.

With these premises we propose to meet again in La Palma to consolidate the scientific interest of stellar pulsations and to be prepared to exploit the large-scale surveys, both photometric and spectroscopic.