Water Masers in Orion

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Abstract
Measurements of the 616 → 523 line of H2O at 1.3 cm in the Orion region of star formation are reported. With a spatial resolution of ≈ 01, H2O maser emission was detected in two regions: Orion BN/KL and Orion S. The well-known masers in the BN/KL region are distributed in a 30'' by 30'' area. The "shell" masers, within the BN/KL region, are distributed in a 2'' by 05 strip centered on radio source I and are offset from IRc2. The average shell maser spectrum is doubly peaked, resembling the spectrum of the v = 1 SiO masers. The shell masers have deconvolved sizes of 24-38 AU, slightly smaller than the synthesized beam. Newly detected H2O masers in the Orion S region are distributed in a 15'' by 20'' area. One cluster of masers in the Orion S region is found in a thin 06 strip. The velocity range of the masers in this cluster is nearly 65 km s-1. We suggest that this cluster of masers is associated with the energetic source of the Orion S molecular outflow. A search in the Orion S region for associated maser emission in the ground-state OH main lines and the 92 → 101A+ and 62 → 61E lines of CH3OH gave only upper limits, as did a search for centimeter-wavelength continuum. Near-infrared images of the Orion region are presented in the J, H, and K bands. Three objects with very red near-infrared colors were detected in the Orion S region, near the H2O masers and the previously detected millimeter-wavelength dust continuum peak. One of these objects exhibits near-infrared colors consistent with a B2 zero-age main-sequence star. Although this object may heat the northern part of the Orion S dust cloud, its luminosity and separation from the dust maximum make it unlikely that it alone heats the entire Orion S region. More likely, the primary heat source of the Orion S region is deeply embedded in dust and completely extincted in the near-infrared.