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CONTEXT: The chemistry in the inner few thousand AU of accreting envelopesaround young stellar objects is predicted to vary greatly with far-UV and X-rayirradiation by the central star. Aim We search for molecular tracers ofhigh-energy irradiation by the protostar in the hot inner envelope. METHODS:The Submillimeter Array (SMA) has observed the high-mass star forming regionAFGL 2591 in lines of CS, SO, HCN, HCN(v2=1), and HC15N with 0.6" resolution at350 GHz probing radial scales of 600-3500 AU for an assumed distance of 1 kpc.The SMA observations are compared with the predictions of a chemical modelfitted to previous single-dish observations. RESULTS: The CS and SO main peaksare extended in space at the FWHM level, as predicted in the model assumingprotostellar X-rays. However, the main peak sizes are found smaller thanmodeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, andHC15N, but not SO and HCN(v2=1), show pedestal emissions at radii of about 3500AU that are not predicted. All lines except SO show a secondary peak within theapproaching outflow cone. A dip or null in the visibilities caused by a sharpdecrease in abundance with increasing radius is not observed in CS and onlytentatively in SO. CONCLUSIONS: The emission of protostellar X-rays issupported by the good fit of the modeled SO and CS amplitude visibilitiesincluding an extended main peak in CS. The broad pedestals can be interpretedby far-UV irradiation in a spherically non-symmetric geometry, possiblycomprising outflow walls on scales of 3500 -- 7000 AU. The extended CS and SOmain peaks suggest sulfur evaporation near the 100 K temperature radius.

Energetic radiation and the sulfur chemistry of protostellar envelopes: Submillimeter interferometry of AFGL 2591