Pulsating and nonpulsating stars in Hyades observed by Hipparcos satellite

A study of the stars in the instability strip of Hyades cluster has been performed taking into account the new estimate of the stellar parallaxes. For taking advantage of the improved accuracy of the distances and hence absolute magnitudes it is necessary to separate the photometric effects of close companions, which appear quite common in Hyades. The δ Scuti stars, differently from nonpulsating stars, appear to be located also above the main sequence, and this is due probably to their large rotational velocity. The comparison of the rotational effects on the star position in the color–magnitudediagramwith theoretical model predictions tends to confirm the importance of differential rotation. A brief discussion of θ2 Tau and some remarks on the X–ray emission of other two δ Scuti stars are also reported.