The role of rotation on Petersen diagrams.: Then, (Ω) period ratios

The present work explores the theoretical effects of rotation in calculating the period ratios of double-mode radial pulsating stars with special emphasis on high-amplitude delta Scuti stars (HADS). Diagrams showing these period ratios vs. periods of the fundamental radial mode can be employed as a good tracer of non-solar metallicities and are known as Petersen diagrams (PD). In this paper we consider the effect of moderate rotation on both evolutionary models and oscillation frequencies and show that such effects cannot be completely neglected as has been done until now. In particular we find that differences in period ratios of some hundredths can be obtained even for low-to-moderate rotational velocities (15-50 km s(-1)). The main consequence is, therefore, the confusing scenario generated when trying to fit the metallicity of a given star using this diagram without previous knowledge of its rotational velocity.