Molecular Chemistry as a Probe of Pre-Stellar Core Dynamics: An Unprecedented Exploration of Models
MPIfR, Bonn, Germany
|We present a comprehensive study of the coupling between chemistry and dynamics for a wide variety of prestellar molecular cloud core models, with the aim to probe the initial conditions of star formation and the origin of protostars. Our dynamical models include pure hydrodynamical collapse with various collapse retardation times, and magnetically modulated collapse for various values of the initial mass-to-flux ratio. These models are coupled to a network of chemical reactions that follow the relative abundances for ~100 molecular species, by solving the non-equilibrium chemical reactions simultaneously with the dynamical equations. We explore, through a parameter study, the competing effects of various model parameters in the evolving molecular abundances, including the elemental C/O ratio, the temperature, and the cosmic-ray ionization rate. Although the results generally show significant degeneracies between different models, we identify abundance ratios between particular molecules, the measurement of which would have maximal potential for discrimination between models. In particular, we find that the ratios between NH3 and CO; NH2 and CO; NH3 and HCO+ are sensitive to the evolutionary timescale, and that the ratio between HCN and OH is sensitive to the C/O ratio. We also demonstrate that measurements of the central depletion or enhancement of abundances of certain molecules are good indicators of the dynamics of the core. Finally, we study the effect that non-equilibrium chemistry in dynamical models of collapsing molecular cloud cores has on measurements of the magnetic field in these cores, the degree of ionization, and the mean molecular weight of ions, and we show that significant deviations develop for all these quantitative measures from their commonly adopted values.
Karen Willacy, JPL, USA
Harold W. Yorke, JPL, USA
Neal J. Turner, JPL, USA