Isabel Cardenas Olivares

The delta Scuti star FG Vir. V. The 2002 photometric multisite campaign

A high-accuracy multisite campaign was carried out from 2002 January to May with a photometric coverage of 398 h at five observatories. The concentration on a few selected sites gives better consistency and accuracy than collecting smaller amounts from a larger number of sites. 23 frequencies were detected with a high statistical significance. 6 of these are new. The 17 frequencies found in common with the 1992-1995 data are the modes with highest amplitudes. This indicates that the pulsation spectrum of FG Vir is relatively stable over the ten-year period. Two frequencies have variable amplitudes and phases from year to year as well as during 2002. These were both found to be double modes with close frequencies. For the mode at 12.15 c/d this leads to an apparent modulation with a time scale of ∼ 129 d. The close frequencies at 12.15 c/d are composed of a radial and a nonradial mode, suggesting a similarity with the Blazhko Effect seen in RR Lyrae stars.

Asteroseismology with the WIRE satellite - I. Combining ground- and space-based photometry of the δ Scuti star ϵ Cephei

Aims. We have analysed ground-based multi-colour Stromgren photometry and single-filter photometry from the star tracker on the WIRE satellite of the 6 Scuti star ∈ Cephei. Methods. The ground-based data set consists of 16 nights of data collected over 164 days, while the satellite data are nearly continuous coverage of the star during 14 days. The spectral window and noise level of the satellite data are superior to the ground-based data and this data set is used to locate the frequencies. However, we can use the ground-based data to improve the accuracy of the frequencies due to the much longer time baseline. Results. We detect 26 oscillation frequencies in the WIRE data set, but only some of these can be seen clearly in the ground-based data. We have used the multi-colour ground-based photometry to determine amplitude and phase differences in the Stromgren b - y colour and the y filter in an attempt to identify the radial degree of the oscillation frequencies. We conclude that the accuracies of the amplitudes and phases are not sufficient to constrain theoretical models of e Cep. We find no evidence for rotational splitting or the large separation among the frequencies detected in the WIRE data set. Conclusions. To be able to identify oscillation frequencies in 6 Scuti stars with the method we have applied, it is crucial to obtain more complete coverage from multi-site campaigns with a long time baseline and in multiple filters. This is important when planning photometric and spectroscopic ground-based support for future satellite missions like COROT and KEPLER.

Strömgren photometry of the δ Scuti star 67 UMa

We present preliminary results derived from the data obtained during five observing campaigns in 2001, 2003, 2004, 2006 and 2007, of the δ Set-type variable star 67 UMa, at Sierra Nevada Observatory, Spain. The analysis of the data was performed by means of the Fourier Transform method, and results are shown. The intrinsic b-y, m1, c1 values are derived and the physical parameters are determined.

Multiperiodicity in the Delta Scuti Star HR 4047

HR 4047 (HD 89343, EN UMa, V = 5 92, 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 = 5 77, A8III) and C2 = HD 88815 (V = 6 42, 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 Stromgren 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.