CCD photometric search for peculiar stars in open clusters - VIII. King 21, NGC 3293, NGC 5999, NGC 6802, NGC 6830, Ruprecht 44, Ruprecht 115, and Ruprecht 120

Institute of Astronomy, National Astronomical Observatory, P.O. Box 136, BG-4700 Smolyan, BulgariaReceived 2006 / Accepted 2006ABSTRACTContext. We continue our survey for magnetic chemically peculiar (CP2) stars in galactic open clusters to shed morelight on their origin and evolution.Aims. To study the group of CP2 stars, it is essential to find these objects in different galactic environments and at awide range of evolutionary stages. The knowledge of open clusters ages and metallicities can help to find a correlationof these parameters with the (non-)presence of peculiarities which has to be taken into account in stellar evolutionmodels.Methods. The intermediate band ∆a photometric system samples the depth of the 5200˚A flux depression by comparingthe flux at the center with the adjacent regions with bandwidths of 110˚A to 230 ˚A. It is capable to detect magneticCP2 and CP4 stars with high efficiency, but also the groups of (metal-weak) λ Bootis, as well as classical Be/shell starscan be successfully investigated. In addition, it allows to determine the age, reddening and distance modulus with anappropriate accuracy by fitting isochrones.Results. From the 1677 observed members of the eight open clusters, twenty five CP2 and one Ae stars were identified.Further nineteen deviating stars are designated as questionable due to several reasons. The estimated age, reddeningand distance for the programme clusters were compared with published vales of the literature and discussed in thiscontext.Conclusions. The current paper shows that CP2 stars are present continuously in very young (7Myr) to intermediateage (500Myr) open clusters at distances larger than 2kpc from the Sun.Key words. Stars: chemically peculiar – stars: early-type – techniques: photometric – open clusters and associations:general