EDP Sciences
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Volume 421, Number 3, July III 2004
Page(s) 1113 - 1119
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20035640

A&A 421, 1113-1119 (2004)
DOI: 10.1051/0004-6361:20035640

Modeling the millimeter emission from the Cepheus A young stellar cluster: Evidence for large scale collapse

S. Bottinelli and J. P. Williams

Institute for Astronomy, University of Hawai'i, Honolulu, HI 96822, USA

(Received 6 November 2003 / Accepted 8 April 2004)

Evidence for a large scale flow of low density gas onto the Cepheus A young stellar cluster is presented. Observations of K-band near-infrared and multi-transition CS and N 2H + millimeter line emission are shown in relation to a sub-millimeter map of the cool dust around the most embedded stars. The near-infrared emission is offset from the dust peak suggesting a shift in the location of star formation over the history of the core. The CS emission is concentrated toward the core center but N 2H + peaks in two main cores offset from the center, opposite to the chemistry observed in low mass cores. A starless core with strong CS but weak N 2H + emission is found toward the western edge of the region. The average CS(2-1) spectrum over the cluster forming core is asymmetrically self-absorbed suggesting infall. We analyze the large scale dynamics by applying a one-dimensional radiative transfer code to a model spherical core with constant temperature and linewidth, and a density profile measured from an archival $850~\mu$m map of the region. The best fit model that matches the three CS profiles requires a low CS abundance in the core and an outer, infalling envelope with a low density and undepleted CS abundance. The integrated intensities of the two N 2H + lines is well matched with a constant N 2H + abundance. The envelope infall velocity is tightly constrained by the CS(2-1) asymmetry and is sub-sonic but the size of the infalling region is poorly determined. The picture of a high density center with depleted CS slowly accreting a low density outer envelope with normal CS abundance suggests that core growth occurs at least partially by the dissipation of turbulent support on large scales.

Key words: radio lines: ISM -- stars: formation -- ISM: kinematics and dynamics -- ISM: molecules -- ISM: abundances -- radiative transfer

Offprint request: S. Bottinelli, sandrine@ifa.hawaii.edu

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