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

A. O. Benz*, P. Staeuber, T. L. Bourke, F. F. S. van der Tak, E. F. van Dishoeck, J. K. Jorgensen, E F; Dishoeck Van, J K Jørgensen

*Bijbehorende auteur voor dit werk

OnderzoeksoutputAcademicpeer review

20 Citaten (Scopus)
266 Downloads (Pure)


Context. 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.

Aims. We search for molecular tracers of high-energy irradiation by the protostar in the hot inner envelope.

Methods. The Submillimeter Array (SMA) has observed the high-mass star forming region AFGL 2591 in lines of CS, SO, HCN, HCN(v(2) = 1), and (HCN)-N-15 with 0.6" resolution at 350 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 model fitted to previous single-dish observations.

Results. 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 (HCN)-N-15, but not SO and HCN(v(2) = 1), show pedestal emissions at radii less than or similar to 3500 AU 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.

Conclusions. 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 3500-7000 AU. The extended CS and SO main peaks suggest sulfur evaporation near the 100 K 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.

Originele taal-2English
Pagina's (van-tot)549-558
Aantal pagina's10
TijdschriftAstronomy & astrophysics
Nummer van het tijdschrift2
StatusPublished - nov.-2007

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