A comparison of density structures of a star forming and a non-star-forming globule - DCld303.8-14.2 and Thumbprint Nebula

Abstract

We present a study of radial density structure of the star forming globule, DCld303.8-14.2 (DC303), and a non-star forming globule, Thumbprint Nebula (TPN), using near-infrared data taken with the ISAAC instrument on the Very Large Telescope. We derive the extinction through the globules using the color excess technique and examine the radial density distribution using Bonnor-Ebert and power-law models. The two globules have significantly different density structures. The extinction profile of DC303 is best fitted with a single power-law with an exponent p = 2.29 +/- 0.08. An unstable Bonnor-Ebert model with a dimensionless parameter xi(max) = 23 +/- 3 provides equally good fit to data. The extinction profile of TPN flattens at small radii, making the profile significantly different from the profile of DC303. We are unable to fit the Bonnor-Ebert model for TPN in a robust manner, but derive the lower limit xi(max) >= 8 for the dimensionless outer edge. The density profile derived for TPN is typical compared to recently observed pre-protostellar globules, with high xi(max) value which could be interpreted as the presence of significant additional support or very slow contraction.