Spectroscopic survey of δ Scuti stars^*

I. Rotation velocities and effective temperatures

INSA, ESA-IUE Observatory, P.O. Box 50727, 28080 Madrid, Spain

Received: 2 January 1996
Accepted: 19 July 1996

Abstract

Projected rotational velocities and effective temperatures for Sct stars as well as 41 non–variable stars of similar spectral type and luminosity are presented here. The rotational velocities have been calculated following the method developed in Gray (1992) and effective temperatures have been derived using the Balmer line profiles. The temperatures obtained from this method are shown to be in reasonable agreement with those calculated using the Infrared Flux Method (IRFM) or spectrophotometric methods. This result has allowed us to use our temperatures to compare different photometric calibrations. We find that the calibration given by Moon & Dworetsky (1985) is the most consistent. In the second part of this paper we have studied the relation between the pulsational properties (periods and amplitudes) and the physical parameters ( and T_eff). Where pulsation modes have been determined, the low amplitude δ Scutis tend to be multimode (radial and non–radial) pulsators, consistent with the theory that non–linear coupling between modes acts to limit the amplitude in these stars. We have compared the distribution of for low amplitude δ Scutis and non–variable stars. This shows the δ Scutis have a broader distribution in suggesting that a high rotation velocity may favour pulsation. We find that the large amplitude δ Scuti stars tend to have longer periods, cooler temperatures and lower rotation velocities. Given that the large amplitude stars are also relatively rare all the above are consistent with the hypothesis that these stars are more evolved (sub–giants) than the low amplitude δ Scutis (main sequence or early post–main sequence).