2004/09/30 by A. Crapsi, P. Caselli, C. M. Walmsley +4 · 2 citations
Physics and Astronomy · #Abundance (ecology) #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Chemical evolution #Core (optical fiber) #Deuterium #Fractionation #Protostar #Stellar, planetary, and galactic studies #astro-ph
paper · pdf · doi:10.1086/426472
published as Astrophys.J. 619 (2005) 379-406 · 42 pages, 17 figures, 12 tables, published in ApJ. Figures 8 to 15 available in gif format; full resolution version can be downloaded at http://cfa-www.harvard.edu/~acrapsi/publications/ Replaced with final version as published on the journal
openalex publication_date 2005/01/20 · arxiv created 2005/01/24 · arxiv updated 2009/12/01 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
We have undertaken a survey of N 2 H + and N 2 D + toward 31 low-mass starless cores using the IRAM 30 m telescope. Our main objective has been to determine the abundance ratio of N 2 D + and N 2 H + toward the nuclei of these cores and thus to obtain estimates of the degree of deuterium enrichment, a symptom of advanced chemical evolution according to current models. We find that the N (N 2 D + )/ N (N 2 H + ) ratio is larger in more "centrally concentrated cores" with larger peak H 2 and N 2 H + column density than the sample mean. The deuterium enrichment in starless cores is presently ascribed to depletion of CO in the high density (>3 × 10 4 cm -3 ) core nucleus. To substantiate this picture, we compare our results with observations in dust emission at 1.2 mm and in two transitions of C 18 O. We find a good correlation between deuterium fractionation and N (C 18 O)/ N (H 2 ) 1.2 mm for the nuclei of 14 starless cores. We thus identified a set of properties that characterize the most evolved, or "prestellar," starless cores. These are higher N 2 H + and N 2 D + column densities, higher N (N 2 D + )/ N (N 2 H + ), more pronounced CO depletion, broader N 2 H + lines with infall asymmetry, higher central H 2 column densities, and a more compact density profile than in the average core. We conclude that this combination of properties gives a reliable indication of the evolutionary state of the core. Seven cores in our sample (L1521F, Oph D, L429, L694, L183, L1544, and TMC 2) show the majority of these features and thus are believed to be closer to forming a protostar than are the other members of our sample. Finally, we note that the subsample of Taurus cores behaves more homogeneously than the total sample, an indication that the external environment could play an important role in the core evolution.