  We investigate possible interpretations of the new periodic B- and A-type
variable stars discovered in NGC 3766. They lie in the region of the
Hertzsprung-Russell diagram between slowly pulsating B and delta Sct stars, a
region where no pulsation is predicted by standard models of pulsating stars.
We show that the two other possible causes of periodic light curve variations,
rotational modulation and binarity, cannot provide a satisfactory explanation
for all the properties observed in those stars either. The question of their
origin is thus currently an open issue.
