7. Conclusions

We have discovered six new and confirmed six Bootis stars. Furthermore, eleven candidates for membership in this group have been identified or confirmed. This yields more than ten positive detections out of 120 observed stars, showing that the proposed photometric selection criteria (see Sect. 2 (click here)) in the Strömgren (as well as in the Geneva) photometric system is able to select stars with a good probability of membership in the Bootis group.
With four established Bootis stars (HD36726, HD 290492, HD290799 and HD294253) in the Orion OB1 association (10⁶<age<10⁷yr), two candidates (see Sect. 6.2 (click here)) in NGC2264 (age ) and one candidate (HD224964) in the Blanco1cluster (age ), it is evident that Bootis stars exist in young open clusters. On the other hand, the question of whether Bootis stars exist in intermediate age and old open clusters (age10⁷yr) remains open. Most, but not all of the A-type stars in 10 intermediate age clusters (e.g. Persei, Praesepe, Pleiades, Hyades) were reclassified and no Bootis candidate was found (Gray & Corbally 1993). This seems to point to an upper limit for the Bootis phenomenon

(10⁷yr), supporting the accretion theory. Further observations in open clusters are very much needed to establish a time scale for the Bootis phenomenon.

Acknowledgements

This research was carried out within the working group Asteroseismology-AMS with funding from the Fonds zur Förderung der wissenschaftlichen Forschung (project S7303-AST). Use was made of the Simbad database, operated at CDS, Strasbourg, France.