4 Conclusions

We have searched for and detected new variable stars in NGC6231. The available data allowed us to determine variability and derive preliminary frequency solutions as estimates of the time scales and amplitudes of the variations. We found 17 new variable stars of which, among the fainter stars, three are $\delta$ Scuti stars (SBL0306, SBL0432 and SBL595) and three are $\gamma$ Doradus candidates (SBL0628, SBL0646 and ASK0171). Among the brighter stars, one or two are new $\beta$ Cephei candidates (SBL0456, SBL0515) while three stars are SPB candidates (SBL0275, SBL0394 and SBL0461). One variable, SBL0417, is a PMS star according to SBL. For 6 stars, no good classification could be suggested based on the present data (SBL0332, SBL0417, SBL0508, SBL0598, SBL0636 and SBL1949).

We have furthermore discussed new data on a known $\delta$ Scuti star (SBL0455), where we were able to confirm the variability, and six known $\beta$ Cephei stars (SBL0226, SBL0268, SBL0303, SBL0486, SBL0653 and SBL0712). For two suspected $\beta$ Cephei stars, SBL0353 and SBL0437 (BE85), we also suspect variability but need more data before a definite detection can be made. We observed incomplete eclipses for two EBs (SBL0505 and SBL0521).

Acknowledgements

T.A., C.S. and M.R.K. acknowledge financial support from the Belgian Fund for Scientific Research (FWO). This project was supported by the Flemish Ministry for Foreign Policy, European Affairs, Science and Technology, under contract BIL 99/2 and by the Danish Natural Science Research Council through the centre for Ground-Based Observational Astronomy. Our research has made use of the SIMBAD database operated at CDS, Strasbourg, France, the NASA Astrophysics Data System and the STSci Digitized sky survey.