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Astron. Astrophys. 354, 1127-1133 (2000)

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HC3N and the ages of dense cores

C. Gwenlan 1, D.P. Ruffle 2, S. Viti 1, T.W. Hartquist 3 and D.A. Williams 1

1 Department of Physics and Astronomy, University College London, Gower Street, London, WC1E 6BT, UK
2 Department of Physics, The Ohio State University, Columbus, Ohio 43210, USA
3 Department of Physics and Astronomy, University of Leeds, Leeds LS2 9JT, UK

Received 15 October 1999 / Accepted 29 December 1999


Fractional abundances of HC3N and a number of other species are presented for dense core models based on a variety of different assumptions. The highest calculated values of the HC3N fractional abundances arise in static models where many species striking grain surfaces are processed in hydrogenation reactions leading to the rapid injection of saturated species into the gas phase; in these models the HC3N is most abundant well before chemical equilibrium is reached. The effects of the various parameters considered are strongly coupled and lead to markedly differing ratios of the HC3N abundance relative to abundances of other species including H2CO, C3H and C4H. Although none of these models is specific to any particular astronomical object, we briefly compare our results with abundances observed in TMC-1. We conclude that the molecular abundances observed in TMC-1 can be accounted for on the basis of models of the type discussed here, and that - although this much-studied object has unusually high molecular abundances - it is not chemically anomalous compared to other dense cores.

Key words: ISM: clouds – ISM: general – ISM: molecules

© European Southern Observatory (ESO) 2000

Online publication: February 25, 2000