The potential of SPATO: Survey of PLATO A-Type stars Oscillation frequencies

Pulsating A-F type stars on the main sequence occupy the region where the classical instability strip intersects the main sequence, a regime in which different excitation mechanisms coexist and overlap in the HR diagram. This degeneracy hinders a clear observational classification and calls for large, homogeneous statistical studies.

To address this, we present SPATO, a new catalogue of oscillation frequencies for A-F type stars in the PLATO LOPS2 field, combining TESS light curves with Gaia DR3 and TIC stellar parameters. SPATO provides a unique dataset in which both stellar parameters and frequency content are consistently derived, including all significant pulsation frequencies down to a well-defined noise level.

Using this catalogue, we find a pulsator fraction of about 60% for $\delta$ Scuti stars, and revisit the classification of $\delta$ Scuti and $\gamma$ Dor variables. The classical 5 c/d boundary does not translate into a clear separation in the HR diagram. Instead, the period-luminosity diagram reveals two dominant populations, with $\delta$ Scuti stars forming a well-defined sequence along the period-luminosity relation and $\gamma$ Dor stars located below it. We propose the low-density region between them as a new purely observational discriminator.

Combining Gaia-based pulsation constants with TESS frequencies, we identify radial modes and show that the fundamental and first overtone define tight, nearly parallel relations. These correlate strongly with stellar radius and surface gravity, enabling $\nu_A$ to act as a proxy for $R$ and $\log g$ with high precision. Higher overtones show larger dispersion, consistent with theoretical expectations and possible misidentification with non-radial modes.

SPATO demonstrates the power of frequency-based catalogues for population studies and provides a reference dataset to identify targets for detailed follow-up and to prepare future analyses with PLATO.