1999A&A...344..499Z

We present the first sub-arsecond 8-13 µm images of the young stellar cluster AFGL 4029, obtained using the camera CAMIRAS mounted at the Canada-France-Hawaii Telescope. The two dominant components of the cluster, a highly obscured young stellar object (YSO) and a compact H II region excited by a B1 star, are both spatially resolved and show the 11.3µm band in emission. The dust composition and excitation in the AFGL 4029 HII region appear similar to those in other compact HII regions of moderate excitation observed by ISO-SWS. In addition, we observe that the 11.3µm feature/continuum ratio decreases toward the main exciting star on scales ≤8800AU. The large extent of the mid-infrared emission from the YSO is so far a unique example among deeply embedded objects. It suggests that there is no simple trend relating the mid-IR size and the evolutionary status in young stars. The emission arises in optically thin circumstellar dust, possibly in a cavity carved by the bipolar outflow. An optical and near-infrared reflection nebulosity present 5" away from the YSO is also detected in the mid infrared. It is particularly bright in the 11.3µm feature, with a feature/continuum ratio ∼4 comparable to that seen in prototypical reflection nebulae. Finally, mid-IR emission associated with an optical jet knot in the same zone suggests that shocks, by creating small particles, might explain the high surface brightness in this region.