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Paper: Searching for Massive Pre-Stellar Cores through Observations of N2H+ and N2D+
Volume: 387, Massive Star Formation: Observations Confront Theory
Page: 30
Authors: Fontani, F.
Abstract: We have determined the deuterium fractionation and the integrated CO depletion factor (ratio between expected and observed CO abundance) in a sample of high-mass protostellar candidates, in order to understand whether the earliest evolutionary stages of massive stars have chemical characteristics similar to their low-mass counterparts. We have observed N2H+, N2D+ and C17O with the IRAM-30m telescope, and the sub-millimeter continuum with SCUBA at the JCMT towards 10 well-known high-mass protostellar candidates. N2D+ lines have been detected in 7 of the 10 sources observed, with an average value of the column density ratio N(N2D+)/N(N2H+) ∼ 0.015 (3 orders of magnitude higher than the interstellar D/H abundance). The majority of the observed sources has an integrated CO depletion factor larger than the expected value, with a median value of 3.2. These results indicate the presence of cold and dense gas with physical properties similar to those of low-mass pre-stellar cores.

In one of these sources, IRAS 05345+3157, we have mapped the deuterated gas at high angular resolution, by means of interferometric observations obtained with the Submillimeter Array and the IRAM Plateau de Bure Interferometer.We have detected two condensations in N2D+, with masses of ∼ 2 − 3 and ∼ 9 M and diameters of 0.05 and 0.09 pc, respectively. The masses, the high deuterium fractionation (∼ 0.1) and the line parameters of the N2D+ condensations indicate that they are likely low- to intermediate-mass pre-stellar cores, even though other scenarios are possible.

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