Reddening distribution across the center of the globular cluster ω Centauri

We present new medium-band uvby Stromgren and broadband VI photometry for the central regions of the v globular cluster omega Cen. From this photometry we have obtained differential reddening estimates relative to two other globular clusters ( M13 and NGC 288) using a metallicity-independent, reddening-free temperature index, [ c] equivalent to( u - v) - ( v - b) - 0.2( b - y), for hot horizontal- branch ( HB) stars ( T-eff >= 8500 K). We estimate color excesses of these hot HB stars using optical and near-infrared colors, and we find clumpy extinction variations of almost a factor of 2 within the area of the cluster core. In particular, the greatest density of more highly reddened objects appears to be shifted along the right ascension axis when compared with less reddened ones. These findings complicate photometric efforts to investigate the star formation history of omega Cen.