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Deuterium Chemodynamics of Massive Pre-Stellar Cores

Presentation #506.01 in the session “Astrochemistry 2”.

Published onJan 11, 2021
Deuterium Chemodynamics of Massive Pre-Stellar Cores

High levels of deuterium fractionation of N2H+ (i.e., Dfrac(N2H+) > 0.1) are often observed in pre-stellar cores (PSCs) and detection of N2D+ is a promising method to identify elusive massive PSCs. However, the physical and chemical conditions required to reach such high levels of deuteration are still uncertain, as is the diagnostic utility of N2H+ and N2D+ observations of PSCs. Here we carry out a series of three-dimensional magnetohydrodynamics simulations of a massive, turbulent prestellar core, coupled with a sophisticated deuteration astrochemical network. We investigate the effects of initial ortho-para ratio of H2 (OPRH2), temperature, cosmic ray (CR) ionization rate, CO and N-species depletion factors and prior chemical evolution of the PSC. We find that high CR ionization rates and high depletion factors allow the simulated Dfrac(N2H+) and absolute abundances to match observational values in about one free-fall time. For OPRH2, while a lower initial value helps the growth of Dfrac(N2H+), the spatial structure of deuteration in this case is too widespread compared to observed systems. For an example model with elevated CR ionization rates and significant heavy element depletion, we then study the kinematic and dynamic properties of the core as traced by its N2D+ emission. The core, undergoing quite rapid collapse, exhibits disturbed kinematics in its average velocity map. Still, because of magnetic support, the core often appears kinematically sub-virial based on its N2D+ velocity dispersion. We discuss the implications of our results for massive star formation theories.


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