SEARCH FOR OPTICALLY THICK H II REGIONS AND IONIZED STELLAR WIND FROM LUMINOUS EMBEDDED INFRARED SOURCES

摘要

High-resolution radio continuum observations of 14 protostellar candidates have been obtained using the VLA at 2 cm. The sources were chosen from a compilation of Wynn-Williams. Positive detections were made for W33A, OMC-2 IRS 4, S255 IRS 1, S255N, and NGC 6334V IRS 4, while 3 σ upper limits of 0.15-0.5 mJy were obtained for 11 other sources. Additional 3.6 cm and 2 cm data were also obtained for W33A and OMC-2. In OMC-2 IRS 4, the radio source coincides with the northern source IRS 4N seen in the near-IR. The 3.6 cm emission of this source shows a faint extension in the same direction as the outflow inferred from infrared polarization measurements. The total spectral energy distribution of W33A at radio wavelengths is nearly flat and is consistent with a confined stellar wind model. In NGC 6334V IRS 4, a compact source slightly displaced from the central 20 μm source and extended emission corresponding to the eastern lobe of the bipolar flow observed in the near-IR are seen. The bolometric luminosity inferred from the radio continuum emission assuming optically thin conditions is substantially less than the far-IR luminosity for most of the sources. For deeply embedded high-luminosity young stars, this suggests that either the radio continuum emission is optically thick or the stellar source is still in the pre-main-sequence stage with low ionizing radiation.