5 Conclusion

Our spectroscopic feasibility study based on data taken in May 2001 confirms earlier studies from observations in July/August 1999 and May 2000. All these investigations have shown that it is possible to measure accurate radial velocity curves for PG 1605+072. Three to five frequencies could be detected in the periodograms. The detected frequencies found in the radial velocity studies are very stable (see Tables 2 and 3). However, the amplitudes of the frequencies show drastic temporal changes over a few years. We also have simultaneously measured photometric variations of PG 1605+072 in four wavebands for the first time. The amplitudes in the " $UV_{\rm {B}}$'' band are found to be significantly larger than at larger wavelengths (" $B_{\rm {B}}$'', " $R_{\rm {B}}$'' and " $NIR_{\rm {B}}$''). No phase shifts between the four light curves can be detected.

The time basis of all observations is much too short to resolve the full frequency spectrum of this star. More than 50 frequencies have been resolved in the long photometric study of Kilkenny et al. (1999). Consequently, a new data set with a longer time basis is needed. For that reason we organised a combined photometric and spectroscopic multi-site campaign (PI: U. Heber), termed the MSST (Multi Site Spectroscopic Telescope) project (Heber et al. 2002b). These observations covered a period of one month in May/June 2002. This project is unique in that it combines photometric and spectroscopic data. The data still have to be reduced and analysed. A lot of work remains to be done. Hopefully, we will be able to identify pulsation modes within this large data set and carry out a detailed asteroseismological investigation of PG 1605+072. The feasibility study presented in this paper in concert with all other equivalent studies mentioned in Sect. 4 have paved the way for this aim.

Acknowledgements

The authors would like to thank the Calar Alto staff for their support during our observation run in May 2001. Financial support by the Deutsches Zentrum für Luft- und Raumfahrt (DLR) under grant 50 OR 96029-ZA is gratefully acknowledged. We also thank the Deutsche Forschungs Gemeinschaft (DFG) for a travel grant (HE 1356/33-1) to Calar Alto observatory. BUSCA was realised with financial support by the german Bundesministerium für Bildung, Wissenschaft, Forschung und Technologie (BMBF) through grant 0 3BN114 (4) of Verbundforschung Astronomie/Astrophysik. We thank Simon O'Toole for his valuable comments on the text and contributing a routine to calculate the errors of the amplitudes and phases.