The State-of-the-art HST Astro-photometric Analysis of the Core of ω Centauri. II. Differential-reddening Map∗

We take advantage of the exquisite quality of the Hubble Space Telescope astro-photometric catalog of the core of ω Cen presented in the first paper of this series to derive a high-resolution, high-precision, high-accuracy differential-reddening map of the field. The map has a spatial resolution of 2 × 2 arcsec 2 over a total field of view of about 4.′3 × 4.′3. The differential reddening itself is estimated via an iterative procedure using five distinct color–magnitude diagrams, which provided consistent results to within the 0.1% level. Assuming an average reddening value E ( B − V ) = 0.12, the differential reddening within the cluster’s core can vary by up to ±10%, with a typical standard deviation of about 4%. Our differential-reddening map is made available to the astronomical community in the form of a multi-extension FITS file. This differential-reddening map is essential for a detailed understanding of the multiple stellar populations of ω Cen, as presented in the next paper in this series. Moreover, it provides unique insight into the level of small spatial-scale extinction variations in the Galactic foreground.