  To date, WASP-33 is the only delta Scuti star known to be orbited by a hot
Jupiter. The pronounced stellar pulsations, showing periods comparable to the
primary transit duration, interfere with the transit modeling. Therefore our
main goal is to study the pulsation spectrum of the host star to redetermine
the orbital parameters of the system by means of pulsation-cleaned primary
transit light curves. Between August 2010 and October 2012 we obtained 457
hours of photometry of WASP-33 using small and middle-class telescopes located
mostly in Spain and in Germany. Our observations comprise the wavelength range
between the blue and the red, and provide full phase coverage of the planetary
orbit. After a careful detrend, we focus our pulsation studies in the high
frequency regime, where the pulsations that mostly deform the primary transit
exist. The data allow us to identify, for the first time in the system, eight
significant pulsation frequencies. The pulsations are likely associated with
low-order p-modes. Furthermore, we find that pulsation phases evolve in time.
We use our knowledge of the pulsations to clean the primary transit light
curves and carry out an improved transit modeling. Surprisingly, taking into
account the pulsations in the modeling has little influence on the derived
orbital parameters. However, the uncertainties in the best-fit parameters
decrease. Additionally, we find indications for a possible dependence between
wavelength and transit depth, but only with marginal significance. A clear
pulsation solution, in combination with an accurate orbital period, allows us
to extend our studies and search for star-planet interactions (SPI). Although
we find no conclusive evidence of SPI, we believe that the pulsation nature of
the host star and the proximity between members make WASP-33 a promising system
for further SPI studies.
