2007A&A...475..549B

The chemistry in the inner few thousand AU of accreting envelopes around young stellar objects is predicted to vary greatly with far-UV and X-ray irradiation by the central star. We search for molecular tracers of high-energy irradiation by the protostar in the hot inner envelope.The Submillimeter Array (SMA) has observed the high-mass star forming region AFGL 2591 in lines of CS, SO, HCN, HCN(ν₂=1), and HC¹⁵N with 0.6'' resolution at 350GHz probing radial scales of 600-3500AU for an assumed distance of 1kpc. The SMA observations are compared with the predictions of a chemical model fitted to previous single-dish observations.The CS and SO main peaks are extended in space at the FWHM level, as predicted in the model assuming protostellar X-rays. However, the main peak sizes are found smaller than modeled by nearly a factor of 2. On the other hand, the lines of CS, HCN, and HC¹⁵N, but not SO and HCN(ν₂=1), show pedestal emissions at radii ≲3500AU that are not predicted. All lines except SO show a secondary peak within the approaching outflow cone. A dip or null in the visibilities caused by a sharp decrease in abundance with increasing radius is not observed in CS and only tentatively in SO.The emission of protostellar X-rays is supported by the good fit of the modeled SO and CS amplitude visibilities including an extended main peak in CS. The broad pedestals can be interpreted by far-UV irradiation in a spherically non-symmetric geometry, possibly comprising outflow walls on scales of 3500-7000AU. The extended CS and SO main peaks suggest sulfur evaporation near the 100K temperature radius. The effects of the corresponding abundance jumps may be reduced in visibility plots by smoothing due to inhomogeneity at the evaporation radius, varying by ±10% or more in different directions.