Chemical evolution in the early phases of massive star formation: II. Deuteration

T. Gerner, Y. L. Shirley, H. Beuther, D. Semenov, H. Linz, T. Albertsson, T. T. Henning

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Abstract

The chemical evolution in high-mass star-forming regions is still poorly constrained. Studying the evolution of deuterated molecules allows distinguishing between subsequent stages of high-mass star formation regions based on the strong temperature dependence of deuterium isotopic fractionation. We observed a sample of 59 sources including 19 infrared dark clouds, 20 high-mass protostellar objects, 11 hot molecular cores and 9 ultra-compact Hii regions in the (3-2) transitions of the four deuterated molecules, DCN, DNC, DCO+, and N2D+ as well as their non-deuterated counterparts. The overall detection fraction of DCN, DNC, and DCO+ is high and exceeds 50% for most of the stages. N2D+ was only detected in a few infrared dark clouds and high-mass protostellar objects. This may be related to problems in the bandpass at the transition frequency and to low abundances in the more evolved, warmer stages. We find median D/H ratios of 0.02 for DCN, 0.005 for DNC, 0.0025 for DCO+, and 0.02 for N2D+. While the D/H ratios of DNC, DCO+, and N2D+ decrease with time, DCN/HCN peaks at the hot molecular core stage. We only found weak correlations of the D/H ratios for N2D+ with the luminosity of the central source and the FWHM of the line, and no correlation with the H2 column density. In combination with a previously observed set of 14 other molecules (Paper I), we fitted the calculated column densities with an elaborate 1D physico-chemical model with time-dependent D-chemistry including ortho- and para-H2 states. Good overall fits to the observed data were obtained with the model. This is one of the first times that observations and modeling were combined to derive chemically based best-fit models for the evolution of high-mass star formation including deuteration.

Original languageEnglish (US)
Article numberA80
JournalAstronomy and astrophysics
Volume579
DOIs
StatePublished - Jul 1 2015

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Keywords

  • Astrochemistry
  • Evolution
  • ISM: molecules
  • Stars: early-type
  • Stars: formation

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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