The S140 core: Aperture synthesis HCO(+) and SO observations

We present 5 sec-8 sec resolution images of the S140 region in the HCO(+) J = 1-0 and SO JK = 22 11 lines. The maps encompass the well-known S140 dense core, bipolar outflow, and photodissociation region. Unlike previous aperture synthesis maps of molecular tracers in this source, the HCO(+) images, constructed from a combination of Hat Creek millimeter-array data and National Radio Astronomy Observatory (NRAO) 12 m telescope data, show significant structure in the dense gas associated with the embedded cluster. The brightest emission in the HCO(+) maps arises from the periphery of the bipolar flow, suggesting the limb-brightened edges of a cavity with an apex at IRS 1. Although HCO(+) abundance variations might be expected as a result of shock processing, comparisons with CO isotope data indicate no significant differences between the ambient material and the low-velocity outflow (less than 10 km/sec). The SO maps provide evidence for variations of at least an order of magnitude in SO column density in the quiescent gas on 10 sec scales, with localized enhancements to the north and west of the embedded cluster. SO emission was not detected at velocities characteristic of the outflow. No compact 89 GHz continuum emission was detected from the IRS sources to a 3 sigma limit of 60 Mjy, consistent with previous mesurements. In an appendix we discuss the effect of 'holes' in the (u,v) sampling on synthesis imaging extended molecular emission. We derive expressions to quantify the effects of holes for Gaussian and uniform disk source distributions. We note that while synthesis observations are often said to be 'sensitive' to structures on scales lambda/5min, where Smin is the length of the shortest baseline, the central brigthness recovered from a Gaussian distribution characterized by full width at half maximum (FWHM) = lambda/5min is only about 3%. If the S140 HCO(+) data are typical of molecular cloud sources, then the central hole gives rise to more significant image distortions than many scattered outer holes.