High Spatial Resolution CN and CS Observation of Two Regions of Massive Star Formation

Abstract

Molecular line CN, CS and mm continuum observations of two intermediate- to high-mass star-forming regions - IRAS20293+3952 and IRAS19410+2336 - obtained with the Plateau de Bure Interferometer at high spatial resolution reveal interesting characteristics of the gas and dust emission. In spite of the expectation that the CN and CS morphology might closely follow the dense gas traced by the dust continuum, both molecules avoid the most central cores. Comparing the relative line strengths of various CN hyperfine components, this appears not to be an opacity effect but to be due to chemical and physical effects. The CN data also indicate enhanced emission toward the different molecular outflows in the region. Regarding CS, avoiding the central cores can be due to high optical depth, but the data also show that the CS emission is nearly always associated with the outflows of the region. Therefore, neither CS nor CN appear well suited for dense gas and disk studies in these two sources, and we recommend the use of different molecules for future massive disk studies. An analysis of the 1 and 3mm continuum fluxes toward IRAS20293+3952 reveals that the dust opacity index beta is lower than the canonical value of 2. Tentatively, we identify a decreasing gradient of beta from the edge of the core to the core center. This could be due to increasing optical depth toward the core center and/or grain growth within the densest cores and potential central disks. We detect 3mm continuum emission toward the collimated outflow emanating from IRAS20293+3952. The spectral index of alpha ~ 0.8 in this region is consistent with standard models for collimated ionized winds.