Tracing FUV Radiation in the Embedded Phase of Star Formation

Molecules containing one or a few hydrogen atoms and a heavier atom (hydrides) have been predicted to trace FUV radiation. In some chemical models, FUV emission by the central object or protostar of a star forming region greatly enhances some of the hydride abundances. Two massive regions, W3 IRS5 and AFGL 2591, have been observed in hydride lines by HIFI onboard the {\it Herschel Space Observatory}. We use published results as well as new observations of CH$^+$ towards W3 IRS5. Molecular column densities are derived from ground state absorption lines, radiative transfer modeling or rotational diagrams. Models assuming no internal FUV are compared with two-dimensional models including FUV irradiation of outflow walls. We confirm that the effect of FUV is clearly noticeable and greatly improves the fit. The most sensitive molecules to FUV irradiation are CH$^+$ and OH$^+$, enhanced in abundance by many orders of magnitude. Modeling in addition also full line radiative transfer, Bruderer et al (2010b) achieve good agreement of a two-dimensional FUV model with observations of CH$^+$ in AFGL 2591. It is concluded that CH$^+$ and OH$^+$ are good FUV tracers in star-forming regions.Comment: EAS Publications Series, 5th Zermatt conference on Conditions and impact of star formation: New results with Herschel and beyond (invited), submitte

X-RAY CHEMISTRY IN THE ENVELOPES AROUND YOUNG STELLAR OBJECTS

We have studied the influence of X-rays from a massive young stellar object (YSO) on the chemistry of its own envelope by extending the models of Doty et al. (2002) and Stäuber et al. (2004a). The models are applied to the massive star-forming region AFGL 2591 for different X-ray luminosities and plasma temperatures. Enhanced column densities for several species are predicted. In addition we present first detections of CO + and SO + toward AFGL 2591.These molecular ions are believed to be high-energy tracers. Herschel-HIFI will be able to observe other tracers like CH and CH + whereas ALMA is well suited to measure the size and geometry of the emitting region. 1