The Visible and Near‐Infrared Dust Opacity Law in the HH 30 Circumstellar Disk

Abstract

We present new images of the scattered-light disk around HH 30 at 0.44 and 0.81 μm. We model these images and an existing 2.04 μm image by using a multiple-scattering code, varying and fitting for the disk parameters and the dust opacity ratios at these wavelengths. A wide range of different disk geometries provide adequate fits to the data; there is no single best-fit geometry. In particular, the fits cannot resolve the ambiguity between the power-law indices in surface density and scale height. On the other hand, the inclination, opacity-mass product, scale height, and to a lesser degree the extinction to the star are relatively tightly constrained. Despite the ambiguity in geometry, we conclude that the dust opacity in the scattering layers of the outer parts of the HH 30 circumstellar disk drops from 0.44 to 2.04 μm, but by less than in the low-density ISM. The median fit shows a drop by a factor of less than 2. This result is robust to reasonable changes in the disk density distribution. It suggests that moderate grain growth has occurred but that small grains still dominate the visible and near-infrared opacity.