The deeply embedded source that drives the protostellar outflow in AFGL 437: Evidence from near-infrared polarimetric imaging

Near-infrared polarimetric images of AFGL 437 reveal that this source, previously identified as a compact cluster of four infrared stars, is in fact an extensive reflection nebula containing more than two dozen and possibly more than five dozen sources. Our near-infrared polarimetric maps of this nebulosity, reinforced with evidence from the nebular colors and the position of the associated water maser, provide strong evidence that WK 34-a deeply embedded young stellar object (YSO)-drives the molecular outflow known to emanate from AFGL 437. At 2.2 mu m, this YSO illuminates a red bipolar reflection lobe that stretches to the north, curves toward the northeast, and is approximately parallel to the molecular outflow direction. WK 34 appears similar to the deeply embedded sources that illuminate near-infrared reflection nebulae and likely drive molecular outflows in L1287, NGC 7129, and OMC-1. As in the cases of L1287 and NGC 7129, the identification of an embedded YSO as the most likely source of the AFGL 437 outflow appears to eliminate more evolved, optically identified sources as active drivers of the outflow. Together, the infrared polarimetric imaging results of AFGL 437, L1287, and NGC 7129 indicate that in many, if not most, cases where an optically identified pre-main-sequence star lies near the apex of a bipolar outflow, upon closer inspection we are likely to find a younger, more deeply embedded source.