Abstract
Using the Very Large Array, we have observed the H66α radio recombination line (RRL) emission at 1.3 cm and the H52α RRL emission at 7 mm toward the ultracompact H II region M17-UC1 and the nearby arc-shaped structure to the east. The angular resolution of the data is 1''-2''. The compact H II region (deconvolved size ~06 or 0.006 pc) is one of a number of H II regions with broad (≥35 km s-1) RRLs. The line parameters of the nearby arc of ionized emission (hereafter the Arc), about 1'' or 0.01 pc to the east of UC1, are remarkably constant over an area of 165 × 3'' (0.17 pc × 0.03 pc). The derived LTE electron temperature from the H66α line (T) is 6600 K in M17-UC1 and 8200 K in the Arc region. H2O maser emission at 1.3 cm from the region of M17-UC1 was observed in the D array with a beam of 4''. Observations of the H2O maser emission toward M17-UC1 reveal four masers within 30'' of M17-UC1; two of these sources were previously known. We discuss the region near M17-UC1 as an example of shock-induced star formation consisting of a hot, young, massive star surrounded by ionized material, perhaps resulting from a stellar wind outflow. We compare M17-UC1 with the six other known examples of broad-line RRL emission from ultracompact H II regions.
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