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Chemical Signatures of the Evolutionary State of Cores

Published online by Cambridge University Press:  23 September 2016

Yuri Aikawa
Yuri Aikawa*
Affiliation:
Department of Earth and Planetary Sciences, Kobe University, Kobe 657-8501, Japan

Abstract

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Recent observations with high angular resolution revealed chemical differentiation in several prestellar cores; while N2H+ emission peaks at the core center, CO, CS and CCS emission peaks are offset from the center. Molecular abundances also vary among cores; some cores have high CCS abundance and low N2H+ abundance, but others have less CCS and more N2H+. Numerical calculations of a chemical-reaction network in contracting cores show that these differentiations and variations can be diagnostics of physical evolution of cores, because molecular abundances and distributions are determined by the balance between the dynamical and chemical time scales. In prestellar cores, low temperatures and high densities cause adsorption of molecules onto grains. Depletion time scale varies among species; early-phase species deplete first because of destruction via gas-phase reactions in addition to the adsorption. N2H+ is the last to deplete because of the low adsorption energy of its parent molecule N2 and depletion of main reactants such as CO. Molecular D/H ratio is another probe of core evolution, since it increases as the adsorption proceeds.

Type
Part 2: From Molecular Clouds to Protostellar Cores
Information
Symposium - International Astronomical Union , Volume 221: Star Formation at High Angular Resolution , 2004 , pp. 67 - 74
Copyright
Copyright © Astronomical Society of the Pacific 2004 

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