2007ApJ...661..926M

The internal structure of the dark globule CB 52 is investigated by means of broadband imaging in the optical and near-IR spectral range. By exploiting the extinction of the stellar light within this object, we derive observational parameters suitable to infer the internal structure of this cloud. Extinction maps were obtained at different wavelengths by using both stellar counts and two-color diagrams. While in the optical region the extinction is better evaluated at the cloud boundaries, the internal regions are more conveniently probed in the near-IR, so a combined map was derived. The total-to-selective extinction ratio R_V was also observed to increase toward the inner regions, and a plot versus the extinction A_Vsuggests that grain growth processes are active in this cloud. The statistical fluctuation of the A_V, estimated in the line of sight of the background stars, is investigated by comparing the observed stellar colors with those of the unreddened stars. The dispersion σ_AV, derived from optical observations, is found to be almost independent of the mean extinction, A_V, while by using near-IR data we find a more complex behavior: the σ_AV versus A_Vrelation increases until A_V∼6 and then decreases for larger extinctions. This is discussed in the framework of a simple model, suggesting that a clumpy and clustered structure can explain the observations in the inner regions, while outside the cloud the mass distribution remains more homogeneous.