Evidence of warm and dense material along the outflow of a high-mass YSO
Abstract
Context: Outflow cavities in envelopes of young stellar objects (YSOs) have been predicted to allow far-UV (FUV) photons to escape far from the central source, with significant observable effects, especially if the protostar is a forming high-mass star suspected of emitting a copious amount of FUV radiation. Indirect evidence of this picture has been provided by models and unresolved single-dish observations, but direct high-resolution data are necessary for confirmation. Previous chemical modeling has suggested that CS and HCN are good probes of the local FUV field, so make good target species.
Aims: We directly probe the physical conditions of the material in the outflow walls to test this prediction.
Methods: Interferometric observations of the CS(7-6) and HCN(4-3) rotational lines in the high-mass star-forming region
Results: CS and HCN emission was found in spatial coincidence in extended sources displaced up to 7 arcsec from the position of the young star. Their line widths are small, excluding major shocks. Chemical model calculations predict an enhanced abundance of the two molecules in warm, dense, and FUV irradiated gas. Hot dust observed between the molecular emission and the outflow accounts for the necessary attenuation to prevent photodissociation of the molecules.
Conclusions: The SMA data suggest that the outflow walls are heated and chemically altered by the FUV emission of the central high-mass object, providing the best direct evidence yet of large-scale direct irradiation of outflow walls.
- Publication:
-
Astronomy and Astrophysics
- Pub Date:
- August 2009
- DOI:
- 10.1051/0004-6361/200912620
- Bibcode:
- 2009A&A...503L..13B
- Keywords:
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- stars: formation;
- ISM: molecules;
- stars: individual: AFGL 2591