Extinction with 2MASS: Star Counts and Reddening toward the North America and Pelican Nebulae

Abstract

We propose a general method for mapping the extinction in dense molecular clouds using Two Micron All Sky Survey near-infrared data. The technique is based on the simultaneous utilization of star counts and colors. These two techniques provide independent estimations of the extinction, and each method reacts differently to foreground star contamination and to star clustering. We take advantage of both methods to build a large-scale extinction map (25 × 25) of the North America and Pelican Nebulae complex. With Ks star counts and H-Ks color analysis the visual extinction is mapped up to 35 mag. Regions with visual extinction greater than 20 mag account for less than 3% of the total mass of the cloud. Color is generally a better estimator for the extinction than star counts. Nine star clusters are identified in the area, seven of which were previously unknown.