EDP Sciences
Free Access
Volume 438, Number 1, July IV 2005
Page(s) 169 - 185
Section Interstellar and circumstellar matter
DOI https://doi.org/10.1051/0004-6361:20042267

A&A 438, 169-185 (2005)
DOI: 10.1051/0004-6361:20042267

Optimal column density measurements from multiband near-infrared observations

M. Lombardi1, 2

1  European Southern Observatory, Karl-Schwarzschild-Straße 2, 85748 Garching bei München, Germany
    e-mail: mlombard@eso.org
2  University of Milan, Department of Physics, via Celoria 16, 20133 Milan, Italy

(Received 27 October 2004 / Accepted 22 March 2005)

We consider from a general point of view the problem of determining the extinction in dense molecular clouds. We use a rigorous statistical approach to characterize the properties of the most widely used optical and infrared techniques, namely the star count and the color excess methods. We propose a new maximum-likelihood method that takes advantage of both star counts and star colors to provide an optimal estimate of the extinction. Detailed numerical simulations show that our method performs optimally under a wide range of conditions and, in particular, is significantly superior to the standard techniques for clouds with high column-densities and affected by contamination by foreground stars.

Key words: dust, extinction -- methods: statistical -- ISM: clouds -- infrared: ISM -- stars: formation

© ESO 2005