TY - JOUR

T1 - Energetic radiation and the sulfur chemistry of protostellar envelopes

T2 - Submillimeter interferometry of AFGL 2591

AU - Benz, A. O.

AU - Stäuber, P.

AU - Bourke, T. L.

AU - Van Der Tak, F. F.S.

AU - Van Dishoeck, E. F.

AU - Jørgensen, J. K.

PY - 2007/11/1

Y1 - 2007/11/1

N2 - 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(V2 = 1), and HC15N 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 HC15N, but not SO and HCN(V2 = 1), show pedestal emissions at radii 53500 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.

AB - 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(V2 = 1), and HC15N 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 HC15N, but not SO and HCN(V2 = 1), show pedestal emissions at radii 53500 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.

KW - Accretion, accretion disks

KW - Astrochemistry

KW - ISM: molecules

KW - Stars: formation

KW - Submillimeter

KW - X-rays: ISM

UR - http://www.scopus.com/inward/record.url?scp=36549011274&partnerID=8YFLogxK

U2 - 10.1051/0004-6361:20078032

DO - 10.1051/0004-6361:20078032

M3 - Journal article

AN - SCOPUS:36549011274

VL - 475

SP - 549

EP - 558

JO - Astronomy & Astrophysics

JF - Astronomy & Astrophysics

SN - 0004-6361

IS - 2

ER -