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Jes Jørgensenhttp://youngstars.nbi.dk/http://www.nbi.dk/~jeskjshapeimage_2_link_0

In contrast to the formation of low-mass stars, the formation of high-mass stars is relatively poorly understood. There are a number of reasons for this: high-mass stars are rarer and therefore on average further away, the evolution is faster -making it difficult to detect the intermediate stages- and they are generally found in clusters and strongly interact with their environment. Additionally, the envelopes of young high-mass star are chemically and physically complex regions. A large number of sulfur-bearing species are also detected in these types of sources, such as OCS, H2S and SO2. The relative abundances of these species are very interesting, since they could potentially be used as a chemical clock., i.e. their relative abundances depend on the evolutionary stage of the object.

We have a large sub-millimeter line-survey for one such high-mass star, which contains many emission lines for the different sulfur-bearing species. The idea in this project would be to model the emission of these species, and try to compare it to the chemical model by Doty et al. (2004) for the sulfur chemistry and ascertain if it is possible to use these species as a chemical clock and if so what evolutionary stage the region is in. Plan for the project:

  1. Identify the transitions of the sulfur bearing species using the myXCLASS program

  2. Produce a simple LTE model of the line-emitting region using the myXCLASS program

  3. Model the emission using the 3D radiative transfer code LIME using a more realistic source model

  4. Test the chemical clock hypothesis and compare the results with the chemical model by Doty et al. (2004).

Sulfur as a chemical clock for high-mass protostars

Keywords: APEX submillimeter observations; possibly follow-up observations or rad. transfer modeling