Projected rotational velocities () and effective temperatures have been derived for Sct stars as well as for 41 non-variable stars in order to relate the physical parameters of a star with its pulsation parameters. Rotational velocities were calculated using the method developed in Gray (1992) which works well for spectra with moderate resolution and good signal-to-noise.
Effective temperatures were determined by comparing observed profiles with the theoretical profiles of Kurucz (1979a). Extensive comparison was then made between these temperatures and those derived using other methods (Infrared Flux Method, spectrophotometric methods and photometric calibrations). A systematic difference of 100 K between the effective temperatures obtained using the line and the IRFM (Blackwell & Lynas-Gray 1994) was found. No significant differences were found between the effective temperatures derived from and from spectrophotometric methods (Malagnini et al. 1986). The level of agreement with temperatures from photometry depend on the calibration used, the best agreement being with the Moon & Dworetsky calibration (1985).
In the second part of this paper we relate and with the amplitude and period of the stars. There is a clear relation between amplitude and with all the large amplitude pulsators having low rotation velocities. Where modes are known, the large amplitude stars are singe or double-mode radial pulsators whereas the low amplitude stars are multimode pulsators with both radial and non-radial modes excited. The multimode behaviour among low amplitude stars is consistent with the suggestion by Dziembowski (1980) that non-linear coupling between radial and non-radial modes limits the amplitudes. Several stars seem to be anomalous: V1162 Ori is a radial large amplitude pulsator with =46 whereas GN And is a single-mode low amplitude pulsator. In both cases, more extensive observing runs could indicate the presence of new frequencies. Moreover CC And, a multimode large amplitude star (), may indicate an intermediate stage where multimode pulsation and relatively large amplitude can coexist.
Comparing the distribution in of low amplitude Scutis and non-variable stars of the same spectral type, this shows a broader distribution for the Scutis, suggesting that high rotation may excite pulsation.
Comparing the period-temperature relations for the large and low amplitude stars suggests that the large amplitude stars are preferentially cooler and have longer periods. From their values of , , period and their relative scarcity, the explanation proposed by Breger (1980) that the large amplitude Sct stars are more evolved (sub-giants) than the low amplitude Scutis (main sequence or early post-main sequence) is consistent with observation.
We would like to thank Rafael Garrido for helpful comments. The authors would also like to acknowledge the constructive comments of an anonymous referee. This work has made use of the Simbad database, operated at CDS, Strasbourg, France.