SIMBAD references

Differential E_V-I_ variations of up to ∼0.2 mag on a scale of arcminutes across NGC 3201 are presented in the form of an extinction map. This map, created by calculating average E_V-I_ values for stars in small subregions of the field with respect to a fiducial region, greatly improves the appearance of the color-magnitude diagram of the cluster. We describe how we implemented this technique in detail with our data for NGC 3201. A comparison between our map and that of the same region extracted from the COBE DIRBE reddening maps published by Schlegel, Finkbeiner, & Davis in 1998 (hereafter SFD) displays larger scale similarities between the two maps, as well as smaller scale features that show up in our map but not in the SFD map. Several methods of determining an E_V-I_ zero point to add to our differential extinction map are presented. Isochrone fitting proved to be the most successful one, but it produces an average E_V-I_ for the cluster that is smaller by ∼1.5 σ than previously published values. Finally, our results seem to support the statement by Arce & Goodman that the SFD maps overestimate the reddening in regions of high extinction.