Deep FORS1 Observations of the Double Main Sequence of ω Centauri

We present the results of a deep photometric survey performed with the VLT FORS1 aimed at investigating the complex main-sequence structure of the stellar system ? Centauri. We confirm the presence of a double main sequence and identify its blue component (bMS) over a large field of view up to 26' from the cluster center. We found that bMS stars are significantly more concentrated toward the cluster center than the other ``normal'' MS stars. The bMS morphology and its position in the CMD have been used to constrain the helium overabundance required to explain the observed MS morphology