The images provided by the Advanced Camera for Surveys at the Hubble Space Telescope (ACS/HST) has the amazing spacial resolution of 0.05/pixel. Therefore, it could resolve individual stars in nearby galaxies and in particular young blue stars in associations and open clusters of the recent starburts. These data are useful for studies of the extragalactic young population using color magnitude diagrams (CMD) of the stellar groups. However, even with the excellent indicated spatial resolution, the blending of several stars in crowded fields can change the shape of the CMDs. Some of the blending could be handled in the cases they produce particular features on the stellar PSF profile (e.g. abnormal sharpness, roundness, etc). But in some cases, the blend could be difficult to detect, this is the case were a pair or several stars are in the same line of sight (e.g. observed in the same pixel). In this work, we investigated the importance of the blending effect in several crowded regions, using both numerical simulations and real ACS/HST data. In particular, we evaluated the influence of this effect over the CMDs, luminosity functions (LFs) and reddening estimations obtained from the observations.
Link to PDF (may not be available yet): P12-4.pdf