  We have analysed the photometric data obtained with the STEREO spacecraft for
558 non-magnetic chemically peculiar (CP) stars to search for rotational and
pulsational variability. Applying the Lomb-Scargle and the phase dispersion
minimisation methods, we have detected photometric variability for 44 objects
from which 35 were previously unknown. The new objects are all bright stars on
the Ecliptic Plane (magnitude range 4.7 < V < 11.7) and will therefore be of
great interest to studies of stellar structure and evolution. In particular,
several show multiple signals consistent with hybrid delta Scuti and gamma
Doradus pulsation, with different periodicities allowing very different regions
of the stellar interior to be studied. There are two subgroups of stars in our
sample: the cool metallic line Am (CP1) and the hot HgMn (CP3) stars. These
objects fall well inside the classical instability strip where delta Scuti,
gamma Doradus and slowly pulsating B-type stars are located. We also expect to
find periods correlated to the orbital period for CP1 objects as they are
mostly members of binary systems. For CP3 stars, rotationally-induced
variability is still a matter of debate. Although surface spots were detected,
they are believed to produce only marginal photometric amplitudes. So, periods
from several hours to a few days were expected for these two star groups. The
remaining 514 stars are likely to be constant in the investigated range from
0.1 to 10 days. In some cases, the presence of blending or systematic effects
prevented us from detecting any reliable variability and in those cases we
classified the star as constant. Finally, we have calibrated the variable stars
in terms of the effective temperature and luminosity in order to estimate
masses and ages. For this purpose we used specifically developed calibrations
for CP stars and, when available, HIPPARCOS parallaxes.
