Chemical Tracers of Pre-Brown Dwarf Cores Formed Through Turbulent Fragmentation

Abstract

A gas-grain time dependent chemical code, UCL_CHEM, has been used to investigate the possibility of using chemical tracers to differentiate between the possible formation mechanisms of brown dwarfs. We model the formation of a pre-brown dwarf core through turbulent fragmentation by following the depth-dependent chemistry in a molecular cloud through the step change in density associated with an isothermal shock and the subsequent freefall collapse once a bound core is produced. Trends in the fractional abundance of molecules commonly observed in star forming cores are then explored to find a diagnostic for identifying brown dwarf mass cores formed through turbulence. We find that the cores produced by our models would be bright in CO and NH₃ but not in HCO⁺. This differentiates them from models using purely freefall collapse as such models produce cores that would have detectable transitions from all three molecules.