  We present an investigation of three chemically peculiar (CP) stars and one
CP star candidate which exhibit photometric periods below 12 hours. New
spectroscopic observations have been acquired which confirm the peculiar nature
of all objects. HD 77013 and HD 81076 are classical CP1 (Am) stars; HD 67983 is
a marginal CP1 (Am: ) star, and HD 98000 is a CP2 (Ap) star. We have procured
observations from the ASAS-3 and SuperWASP archives and obtained additional
photometry in order to verify the results from the sky survey data. We have
derived astrophysical parameters and investigated the positions of our target
stars in the MBol versus log Teff diagram, from which information on
evolutionary status has been derived. We present period analyses and discuss
each object in detail. From the available data, we propose pulsational
variability as the underlying mechanism for the variability in HD 67983, HD
77013 and HD 81076, which offer the opportunity to study the interaction of
atomic diffusion and pulsation. HD 67983 and HD 77013 exhibit multiperiodic
variability in the gamma Doradus frequency realm; HD 81076 is a delta Scuti
star. The CP2 star HD 98000 exhibits monoperiodic variability with a frequency
of f~2.148 c/d (P~0.466 d), which we interpret as the rotational period. If
this assumption is correct, HD 98000 is the alpha2 Canum Venaticorum (ACV)
variable with the shortest period hitherto observed and thus a very interesting
object that might help to investigate the influence of rotational mixing on
chemical peculiarities.
