  Since the discovery of the spectral peculiarities of their prototype alpha2
Canum Venaticorum in 1897, the so-called ACV variables, which are comprised of
several groups of chemically peculiar stars of the upper main sequence, have
been the target of numerous photometric and spectroscopic studies. Especially
for the brighter ACV variables, continuous observations over about a century
are available, which are important to study long-term effects such as period
changes or magnetic cycles in these objects. The present work presents an
analysis of 165 Ap/CP2 and He-weak/CP4 stars using light curves obtained by the
Solar Mass Ejection Imager (SMEI) between the years 2003 and 2011. These data
fill an important gap in observations for bright ACV variables between the
Hipparcos and TESS satellite missions. Using specifically tailored data
treatment and period search approaches, we find variability in the accuracy
limit of the employed data in 84 objects. The derived periods are in excellent
agreement with the literature; for one star, the here presented solution
represents the first published period. We discuss the apparently constant stars
and the corresponding level of non-variability. From an investigation of our
target star sample in the Hertzsprung-Russell diagram, we deduce ages between
100 Myr and 1 Gyr for the majority of our sample stars. Our results support
that the variable CP2/4 stars are in a more advanced evolutionary state and
that He and Si peculiarities, preferentially found in the hotter, and thus more
massive, CP stars, produce larger spots or spots of higher contrast.
