The evolutionary models described in the accompanying poster (Richard et al., these proceedings) have been tested for pulsations using both the adiabatic code developed by Brassard et al. (1992) and the corresponding non-adiabatic code as first used in Fontaine et al. (1994). For the stars of interest, these codes have the great advantages of being potentially able to treat atmospheric regions, as well as being numerically stable and efficient. The required derivatives were calculated by least-square fitting of spline functions to complete opacity tables constructed at each composition of the evolved model. Since there were some 1500 zones for each model, 1500 such tables were constructed and spline functions were fitted to each of them. They then gave directly the derivatives required for the pulsation calculations (see Fig. 1). Note that models equivalent to 1.70T5.3D1K-3 have already been tested for pulsations by Turcotte et al. (2000).

We present new results on the effects of a strong dipole magnetic field and rotation on p-mode oscillations. We take into account both Coriolis and centrifugal distortion as manifestations of rotation. We apply these improvements to the case of dipole (l = 1) modes. We show that these modes, during the pulsation cycle, move the stellar surface in a plane, which is inclined from both magnetic and rotation axes. In general, the displacement vector describes an ellipse in that plane. This work is devoted to the study of the roAp star pulsations.

We investigated nonradial pulsations in the presence of a dipole magnetic field in a non-rotating 1.7 M⊙ ZAMS star. Formally, like in the case of pulsation-rotation coupling (Lee & Saio, 1986), the angular dependence of the pulsations is expanded into a series of spherical harmonics of different latitudinal degrees l. To start with, we considered only axisymmetric (m = 0) modes under the adiabatic and the Cowling approximations. In contrast to previous studies of pulsation-magnetic field interaction (Dziembowski & Goode, 1996; Bigot et al., 2000; Cunha & Gough, 2000), we retained the latitudinal derivatives of the perturbed quantities.

We apply a code that solves grey radial non-adiabatic pulsation equations with consistent treatment of radiative transfer to the roAp frequency regime. We find evidence for the existence of chromospheric modes at frequencies 2.5 mHz, 3.7 mHz, 4.6 mHz and 5.7 mHz in the equilibrium model we used. We also find that, since the oscillations are not adiabatic at the surfaces of roAp stars, better surface boundary conditions need to be considered in future studies.

We present the preliminary results of our analysis of the precise radial velocity (RV) measurements of the roAp star HR1217. We have obtained over 2000 spectra of this star (54 hours of coverage) covering a complete rotation period using the 2-d coude echelle spectrograph of the McDonald Observatory’s 2.7m telescope. Our RV data show rotational modulation in both the amplitude and phase of the pulsations. The broad-band (covering 110 Å) RV semi-amplitudes of the f2 mode (=2.65 mHz) varied in the range of 25 m s–1 to 200 m s–1.

A way in which we might learn about the physics of the interior of roAp stars is by studying their oscillations. To that aim we have initiated a study in order to investigate what additional constraints might be imposed to the physics of the interior of roAp stars from the study of their oscillation spectra. We have chosen to start this work by studying the well known multi-periodic roAp star HR 1217. The observed data used for HR1217 were L/L⊙=7.8±0.7 and Teff=7400±100 K, from Matthews et al. (1999), Zs=0.009 estimated from Ryabchikova et al. (1997), and Δv=67.91±0.12μHz from Kurtz et al. (1989).

The current state of seismology of δ Scuti stars is reviewed with particular emphasis on seismic signatures of the extension of their mixed central region and of rotation. We refer also to Goupil et al. (2000) and more generally to Breger & Montgomery (2000) for more details.

δ Scuti stars are population I pulsating stars with spectral type A-early F, located on or near the main sequence. They are found in the lower part of the classical instability strip in a HR diagram (Fig. 1). Masses range from ∼ 1.5M⊙ to ∼ 2.5M⊙ and δ Scuti stars are either in a stage of H-core or H-shell burning. On the main sequence, the high temperature sensitivity of the dominant CNO cycle causes a large convective core to develop, which later shrinks leaving behind a gradient ∇μ in the mean molecular weight.

Phase lag, ψT and R, a parameter measuring the departure from adiabaticity, can be derived directly from multicolor photometry. The same quantities can also be calculated from theoretical non-adiabatic pulsation models. We present here some preliminary theoretical results which indicate that these quantities depend on the mixing length parameter used to treat convection in the standard ML theory. The comparison favours models with α values between 1 and 1.5Hp. Non-adiabatic models also predict the observed phase lags for the newly discovered α Dor g-mode pulsating stars.

The location of the δ Scuti variables in the HR diagram is discussed on the basis of HIPPARCOS parallaxes and uvbyβ photometry together with the R00 catalogue (Rodríguez et al., 2000). In particular, the properties of the α Scuti-type pulsators with nonsolar surface abundances (SX Phe, λ Boo, ρ Pup, δ Del and classical Am stars subgroups) are examined.

The latter four classes of stars are spectroscopically defined subclasses with surface abundance anomalies. Although the stars ρ Pup and δ Del are also pulsators, the groups named after these stars should not be regarded as pulsation subclasses of δ Scuti stars. The abundance anomalies in these stars affect the pulsation properties, e.g., the classical Am stars are constant in light or show only small pulsation amplitudes (e.g., HD 1097). These four groups are only a small selection from the bewildering zoo of stars with unusual surface abundances in this temperature region and represent the groups with δ Scuti pulsation.

The distribution of the known δ Scuti-type variables (R00 catalogue, Rodríguez et al., 2000) is analysed on the basis of some primary observational properties such as visual amplitude, period, visual magnitude and rotational velocities. The present distributions are also compared with those resulting from the earlier catalogue by Rodríguez et al. (1994, R94). The contributions from the Hipparcos, OGLE and MACHO long-term monitoring projects are also discussed. These contributions are quite different in the N-ΔV and N-V diagrams, in the sense that the variables discovered by the Hipparcos satellite are much brighter and with shorter periods than those discovered by the OGLE and MACHO projects.

Concerning the N-ΔV diagram, we find that the gap, which was evident in the R94 catalogue for variables with visual amplitudes between 0.m1 to 0.m3, has disappeared. Thus, it seems that there is not a strict separation in two groups relative to the amplitude (low amplitude for variables with ΔV<0.m1 and high amplitude for variables with ΔV>0.m3) for the δ Scuti-type pulsatore.

The power spectra of several δ Scuti stars show close peaks with similar frequencies and amplitudes. Apart from possible observational problems, this can be interpreted in terms of two separate pulsation modes with similar, close frequencies or an artifact of amplitude variability of a single pulsation mode. If sufficient data are available, it is possible to distinguish between the two hypotheses on the basis of expected systematic phase changes associated with the amplitude variations of an assumed single frequency. This phase-shift test has been applied to modes found for BI CMi. In this paper we present the evidence for one of the close frequency pairs found in this star.

Variables listed as δ Scuti-type pulsators in the R00 catalogue (Rodriguez et al., 2000) with periods longer than 0.d25 are examined on a star-by-star basis, in order to discriminate their true nature (δ Scuti, RR Lyr or γ Dor-type). From this study, it seems that three stars (DH Peg, UY Cam and YZ Cap) are RR Lyr pulsators rather than δ Scuti variables. Moreover, two variables (AD Ari and DE Oct) seem to be γ Dor variables with the shortest periods known to date (0.d2699 and 0.d2778, respectively).

On the base of 105 hour photoelectric monitoring, we show that FL Cnc is a multiperiodic δ Set type variable with rapid night-tonight changes of the amplitudes of the periodic components in the Fourier spectra. We observed an event of pulsating frequency doubling on a time scale of a week, which was treated as an azimuthal mode change.

We report a study of time-dependent behaviour of the light variations in the δ Set star AN Lyn, based on an analysis of new time-series CCD observations and existing data. The amplitude of the main frequency increased from 1994 to 2000 at a rate of 0.006 mmag/yr. The light variation of AN Lyn can be explained currently by amplitude variability mixed with multiperiodic pulsation. With the extended data base, results on XX Cyg are also reported.

We present a new Spectroscopic study of the δ Scuti star 20 CVn in order to solve the controversy on the type of pulsation mode of this object.

Spectroscopic observations of the δ Scuti star V480 Tau, obtained during the MUSICOS 1996 campaign (Hao et al., 2001), detected a large number of modes. In order to assess the information available from such data, we compare the observed spectrum of frequencies with the theoretical predictions obtained for models computed by including the effect of fast rotation on global oscillations.

Some results of the photometry multi-site observations of two δ Scuti stars, V624 Tau and HD 23194, are presented. The observations were carried out in the framework of a STEPHI network in 1999. We collected 343 hours of useful data and detected seven frequencies in V624 Tau and two frequencies in HD 23194.

UV Tri was observed photometrically from 1999 to 2000. A period analysis of the data reveals two pulsation frequencies at 9.3299 and 10.8483 c d-1. From uvbyHβ data we derive V = 11.085, b – y = 0.215, m1 = 0.169, c1 = 0.783, and β = 2.775 mag. With these color indices and some calibrations, we obtain Mv = 2.44 mag, Mbol = 2.27 mag, Teff = 7500 K, log L/L⊙ = 0.99 and a distance of ∼536 pc.

HR 4047 (HD 89343, EN UMa, V = 592, A7Vn) was found to be variable (Plume & Percy, 1988) with an amplitude of hundredths of a magnitude. Since then, this star has been observed by HIPPARCOS. Koen (2001), analysing those data, obtained two frequencies 6.43185 c d-1 and 4.31308 c d-1.

Our observations were made at the Observatorio de Sierra Nevada in Spain in 1997 and 1998 with the telescope of 0.9m. The comparisons stars for 1997 were C1 = HD 88983 (V = 577, A8III) and C2 = HD 88815 (V = 642, F2V), while for 1998 we add the check star C3 = HD 90838 (V = 7.30, F2). The photometric data obtained were analyzed using the Fourier Transform method in the Strömgren v filter. The periodogram of the v band data is shown in Fig. 1. The periodogram presents six clear frequencies and after prewhitening these there is still more power, but the frequencies found are not consistent between the different bands. Applying these frequencies to the data of the 1997 and 1998 separately, we obtain the results shown in Table 1. Note that the amplitudes have changed from one year to another. The results of 1998 agree with the two frequencies found by Koen (2001). Fig. 1 shows the light curves of the observed data for both campaigns in the v filter. The points represent the observations while the solid lines represent the fit for the frequencies listed in Table 1. Further observations are needed to obtain a more detailed pulsational behaviour of this star.

A careful analysis of the light curves of comparison stars to the intermediate amplitude δ Scuti star V1162 Ori observed in 1999/2000 within an international campaign (Arentoft et al., 2001) revealed two new variable stars: GSC 4778-00324, a small-amplitude δ Scuti star, and GSC 4778-00001, an eclipsing variable (see http://www.lunarpages.com/bho for a map of the field). Here, we will concentrate on the first of these.

Since the colour indices (Handler, 2000) put GSC 4778-00324 right in the middle of the δ Scuti instability strip, we decided to monitor its variability (Van Cauteren & Lampens, 2000) taking as much advantage as possible from the international campaign on V1162 Ori and adopting the same comparison stars. The new observations were performed between October 1999 and March 2001, mainly from the Greek and Belgian sites, making use of a standard V filter. We collected and used 2866 data points for GSC 4778-00324 (V = 10.26; b − y = 0.20).