2005ApJ...634.1146M

We present near-infrared broadband and polarimetric images of the compact star-forming cluster AFGL 437 obtained with the NICMOS instrument on board HST. Our high-resolution images reveal a well-collimated bipolar reflection nebulosity in the cluster and allow us to identify WK 34 as the illuminating source. The scattered light in the bipolar nebulosity centered on this source is very highly polarized (up to 79%). Such high levels of polarization imply a distribution of dust grains lacking large grains, contrary to the usual dust models of dark clouds. We discuss the geometry of the dust distribution giving rise to the bipolar reflection nebulosity and make mass estimates for the underlying scattering material. We find that the most likely inclination of the bipolar nebulosity, the south lobe inclined toward Earth, is consistent with the inclination of the large-scale CO molecular outflow associated with the cluster, strengthening the identification of WK 34 as the source powering it.