  The chemically peculiar (CP) stars of the upper main sequence are mainly
characterized by strong overabundances of heavy elements. Two subgroups (CP2
and CP4) have strong local magnetic fields which make them interesting targets
for astrophysical studies. This star group, in general, is often used for the
analysis of stellar formation and evolution in the context of diffusion as well
as meridional circulation. In continuation of a long term study of CP stars
(initiated in the 1980ies), we present new results based on photoelectric
measurements for ten open clusters that are, with one exception, younger than
235Myr. Observations in star clusters are favourable because they represent
samples of stars of constant age and homogeneous chemical composition. The very
efficient tool of Delta a photometry was applied. It samples the flux
depression at 5200A typically for CP stars. In addition, it is able to trace
emission line Be/Ae and lambda Bootis stars. Virtually all CP2 and CP4 stars
can be detected via this tool. For all targets in the cluster areas, we
performed a kinematic membership analysis. We obtained new photoelectric Delta
a photometry of 304 stars from which 207 objects have a membership probability
higher than 50%. Our search for chemically peculiar objects results in fifteen
detections. The stars have masses between 1.7 M(Sun) and 7.7 M(Sun) and are
between the zero- and terminal-age-main-sequence. We discuss the published
spectral classifications in the light of our Delta a photometry and identify
several misclassified CP stars. We are also able to establish and support the
nature of known bona fide CP candidates. The new and confirmed CP stars are
interesting targets for spectroscopic follow-up observations to put constraints
on the formation and evolution of CP stars.
