Context : The recent discovery of a transiting planet around WASP-33 , the misalignment of the stellar rotation axis and the planet orbit , the possible existence of an additional planet in the system , and the presence of \delta Scuti pulsations in the hosting star make this system a highly interesting object to help us understand the origin and evolution of giant planets orbiting very close a star .

Aims : High spatial resolution imaging with an adaptive optics system on the W.M .
10m-Keck II telescope allows the study of the presence of the predicted additional planet , and any other objects , constraining the possible formation scenarios of the system .

Methods : In November 2010 , we recorded high spatial resolution images from 1 to 2.5 \mu m using the W.M .
10m-Keck II telescope and its adaptive optics system , obtaining broad ( Jc , Hc , and Kc ) and narrow band ( FeII ) images of the system .
After data reduction , the contrast and angular resolution provided by this instrument allowed us to constraint the multiplicity of this system and to detect one potential companion .

Results : We have found a new object at a distance of 1.961 " \pm 0.003 " from the WASP-33 , with a position angle of 276.32 \pm 0.24 deg .
It could be a dwarf star/ brown dwarf or an extragalactic object .
In the first case , and assuming the same distance from the Sun , the object is 227 AU from the central star .
On the other hand , no additional objects have been found .
This constraints the possible objects in the system , depending on its age and masses .

Conclusions : A potential companion object to WASP-33 was obtained .
The gravitational link must be confirmed , but this object could influence the evolution of the planetary system depending on its orbital eccentricity .
We have ruled-out the existence of additional objects .
For example , objects of 0.8 M _ { \odot } at projected physical distances greater than [ 2 , 5 ] AU , 0.3 M _ { \odot } at projected physical distances greater than [ 11 , 18 ] AU and 0.072 M _ { \odot } at projected physical distances greater than [ 18 , 75 ] AU , depending on the age of the system .