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https://stockholmuniversity.zoom.us/j/940229961
Given the low ionization fraction of molecular clouds, ambipolar diffusion is thought to be an integral process in star formation. However, chemical and radiative-transfer effects, observational challenges, and the fact that the ion-neutral drift velocity is inherently very small render a definite detection of ambipolar diffusion extremely non-trivial. I studied the ion-neutral drift velocity in a suite of chemodynamical, non-ideal magnetohydrodynamic (MHD), 2-dimensional axisymmetric simulations of prestellar cores where I altered the temperature, cosmic-ray ionization rate, visual extinction, mass-to-flux ratio and chemical evolution. Subsequently, I performed a number of non-local thermodynamic equilibrium (non-LTE) radiative-transfer calculations considering various idealized and non-idealized scenarios in order to assess which factor (chemistry, radiative transfer and/or observational difficulties) is the most challenging to overcome in our efforts to detect the ion-neutral drift velocity. I found that temperature has a significant effect in the amplitude of the drift velocity with the coldest modeled cores (T = 6 K) exhibiting drift velocities comparable to the sound speed. Against all odds, I found that, in idealized scenarios (where two species are perfectly chemically co-evolving) the drift velocity "survives" radiative-transfer effects and can be observed. However, I found that observational challenges and chemical effects can significantly hinder our view of the ion-neutral drift velocity. Specifically, I found that the pairs of HCN and HCO+, and NH3 and N2H+, previously used in observational studies of ambipolar diffusion, exhibit significantly different abundance distributions within the modeled clouds and are thus not suitable for probing the ion-neutral drift velocity. Finally, I propose that HCN and HCNH+, being chemically co-evolving, could be used in future observational studies aiming to measure the ion-neutral drift velocity.