Hipparcos parallaxes of high–amplitude δ Scuti stars are used to derive a period–luminosity relation with a scatter of about ±0.1 mag, which is independent from photometric calibrations to absolute luminosities. Comparisonswith several P–L relations from the literature show satisfactory agreement, and all deviations from theHipparcosmean relation canbe explainedby uncertainties in the data avai...

In a photometric variability survey of 131 stars with B . 14 mag, we have found four new δ Scuti stars. We were sensitive to oscillation amplitudes as low as a few mmag. The detection rate of short-period (P < 0.1 d) pulsating variable stars, which may be relevant for planned large variability surveys such as GAIA, POI, and even the LSST, was therefore 3%. All four new variable stars have low p...

In this work we propose a preliminary seismic investigation of δ 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 δ Scuti stars with radial linear instability predictions. A satisfying agreement is reached between the predicted ranges...

We discuss the results of a systematic search for multi-periodic pulsations in Galactic Bulge δ Scuti and RR Lyrae stars. Six " normal " double-mode variables pulsating in two radial modes have been identified (5 δ Scuti-type and 1 RR Lyrae-type). In 37 RR Lyrae stars secondary periodicities very close to the primary pulsation frequency have been detected. These periodicities correspond to nonr...

Despite the shallow convective envelopes of δ Scuti pulsators, solar-like oscillations are theoretically predicted to be excited in those stars as well. To search for such stochastic oscillations, we organized a spectroscopic multisite campaign for the bright, metal-rich δ Sct star ρ Puppis. We obtained a total of 2763 high-resolution spectra using four telescopes. We discuss the reduction and ...

As a continuation of the study of the newly found δ Scuti star HD 115520, we present a period analysis of recently acquired photometric data covering four nights, as well as some conclusions on the nature of this star.

In an effort to test stellar structure and evolution models, analysis of oscillations in A and F stars in open clusters is carried out by the STACC network (Frandsen 1992). In this paper we describe our effort to locate a suitable open cluster in the northern hemisphere for a future multi-site campaign.We present BV Johnson and time series CCDphotometry of four poorly studied open clusters: NGC...

In order to improve the tests of models of stellar evolution, observations giving tighter constraints on the models were initiated by the formation of an informal group STACC (Frandsen, 1992). The purpose of the group is to search for and make observations of δ Scuti stars in open clusters. This paper presents some of the results of the search, mainly for distant open clusters with a rich popul...

In δ Scuti star models, the calculated amplitude ratios and phase differences for multi-colour photometry exhibit a strong dependence on convection. These observables are tools for determination of the spherical harmonic degree, l, of the excited modes. The dependence on convection enters through the complex parameter f , which describes bolometric flux perturbation. We present a method of simu...

We present an analysis of the pulsation behaviour of the δ Scuti stars 7 Aql (HD 174532) and 8 Aql (HD 174589) – a new variable star – observed in the framework of STEPHI XII campaign during 2003 June–July. 183 hours of high precision photometry were acquired by using four-channel photometers at three sites on three continents during 21 days. The light curves and amplitude spectra were obtained...