New constraints on the initial parameters of low-mass star formation from chemical modeling

The complexity of physico-chemical models of star formation is increasing, with models that take into account new processes and more realistic setups. These models allow astrochemists to compute the evolution of chemical species throughout star formation. Hence, comparing the outputs of such models to observations allows to bring new constraints on star formation. The work presented in this paper is based on the recent public release of a database of radiation hydrodynamical low-mass star formation models. We used this database as physical parameters to compute the time dependent chemical composition of collapsing cores with a 3-phase gas-grain model. The results are analyzed to find chemical tracers of the initial physical parameters of collapse such as the mass, radius, temperature, density, and free-fall time. They are also compared to observed molecular abundances of Class 0 protostars. We find numerous tracers of the initial parameters of collapse, except for the initial mass. More particularly, we find that gas phase CH3CN, NS and OCS trace the initial temperature, while H2CS trace the initial density and free-fall time of the parent cloud. The comparison of our results with a sample of 12 Class 0 low mass protostars allows us to constrain the initial parameters of collapse of low-mass prestellar cores. We find that low-mass protostars are preferentially formed within large cores with radii greater than 20000 au, masses between 2 and 4 Msol, temperatures lower or equal to 15 K, and densities between 6e4 and 2.5e5 part.cm-3, corresponding to free-fall times between 100 and 200 kyrs.