In this work we propose a preliminary seismic investigation of $delta$ Scuti stars in the Pleiades cluster, focusing on potential diagnostics of convection and core-overshooting. Taking into account the effect of fast rotation in the modelling, we compare observed frequencies for 4 $delta$ Scuti stars with radial linear instability predictions. A

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Calculations of energy balance in model stellar atmospheres for cold and moderately cold stars show that the overall energy gained or lost at the Lyman frequencies (lines plus continuum) can be up to 20 orders of magnitude higher than in the rest of the spectrum. Due to the great optical depth at those frequencies, however, monochromatic mean

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We investigate the origin of the discrepancy between the age estimates based on the Color-Magnitude-Diagram and the integrated spectra of 47 Tuc. Using a newly defined Hγ age indicator, with unprecedented power to disentangle the degeneracy between age and metallicity, we confirm the very large spectroscopic age derived for this cluster. We explore