  Context: Stellar pulsations in main-sequence B-type stars are driven by the
kappa-mechanism due to the Fe-group opacity bump. The current models do not
predict the presence of instability strips in the B spectral domain at very low
metallicities. As the metallicity of the SMC is lower than Z=0.005, it
constitutes a very suitable object to test these predictions.
  Aims: The main objective is to investigate the existence of B-type pulsators
at low metallicities, searching for short-term periodic variability in
absorption-line B and Be stars in the SMC. The analysis has been performed in a
sample of 313 B and Be stars with fundamental astrophysical parameters
accurately determined from high-resolution spectroscopy.
  Methods: Photometric light curves of the MACHO project have been analyzed
using standard Fourier techniques and linear and non-linear least squares
fitting methods. The position of the pulsating stars in the HR diagram has been
used to ascertain their nature and to map the instability regions in the SMC.
  Results: We have detected 9 absorption-line B stars showing short-period
variability, two among them being multiperiodic. One star is most likely a beta
Cephei variable and the remaining 8 are SPB stars. The SPB instability strip in
the SMC is shifted towards higher temperatures than the Galaxy. In the Be star
sample, 32 stars are short-period variables, 20 among them multiperiodic. 4.9%
of B stars and 25.3% of Be stars are pulsating stars.
  Conclusions: beta Cephei and SPB stars do exist at the SMC metallicity. The
fractions of SPB stars and pulsating Be stars in the SMC are lower than in the
Galaxy. The fraction of pulsating Be stars in the SMC is much higher than the
fraction of pulsating absorption-line B stars, as in the Galaxy.

Astrophysics