Tracing the evolutionary stage of Bok globules: CCS and NH3⋆
1 Astrophysikalisches Institut und Universitätssternwarte (AIU), Schillergäßchen 2-3, 07745 Jena, Germany
2 Max-Planck-Institut für Astronomie (MPIA), Königstuhl 17, 69117 Heidelberg, Germany
Received: 8 March 2010
Accepted: 12 October 2011
Aims. We investigate a previously proposed correlation between the chemical properties and the physical evolutionary stage of isolated low-mass star-forming regions. The NNH3/NCCS abundance ratio has been proposed to be a potentially useful indicator of the evolutionary stage of cloud cores, and we study its applicability for isolated Bok globules.
Methods. We searched for CCS(21–10) emission in 42 Bok globules both with and without signs of current star formation. A set of NH3 measurements was compiled from measurements available in the literature and from our own observations. The abundance ratio of both molecules is discussed with respect to the evolutionary stage of the objects and in the context of chemical models.
Results. We determine the NNH3/NCCS ratio for 18 Bok globules and find that it is moderately high and roughly similar across all evolutionary stages from starless and prestellar cores towards internally heated cores harboring protostars of Class 0, Class I, or later. We do not find any Bok globules with extremely high CCS abundances analogous to carbon-chain producing regions in dark cloud cores. The observed range of NNH3/NCCS implies that all of the observed Bok globules are in a relatively evolved chemical state.
Key words: ISM: clouds / stars: formation / ISM: molecules / radio lines: ISM
Based on observations obtained with the 100-m telescope of the MPIfR (Max-Planck-Institut für Radioastronomie) at Effelsberg and the 64-m Parkes radio telescope. The Parkes radio telescope is part of the Australia Telescope National Facility which is funded by the Commonwealth of Australia for operation as a National Facility managed by CSIRO.
© ESO, 2012