High angular resolution 7 mm images toward the UC HII region W3(OH)

Context. Recent high angular resolution radio observations of the ultracompact H ii region W3(OH) confirm the presence of an extremely compact (0. ′′05), time-variable source near its center. Aims. We use new, sensitive high angular resolution observations of radio continuum and recombination lines to study the compact source in W3(OH) and the ultracompact H ii region itself. Methods. We reduced and analyzed extensive Jansky Very Large Array observations of W3(OH) in the continuum at 41.0 GHz and in the H54α and He54α lines. Results. Our images confirm there is the compact source and show that it is connected by a linear filament to the brightest part of W3(OH). We discuss several possible explanations for this structure and propose future observations that may clarify its nature.

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