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

The complexity of physico-chemical models of star formation is increasing, with models that take into account new processes and more realistic set-ups, These models allow astrochemisis to compute the evolution of chemical species throughout star formation. Hence, comparing the outputs of such models to observations allows us to bring new constraints on star formation. The work presented in this paper is based on the recent public release of a data base of radiation hydrodynamical low-mass star formation models. We used this data base as physical parameters to compute the time-dependent chemical composition of collapsing cores with a three-phase gas-grain model. The results are analysed 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 rind that gas-phase CH3CN, NS, and OCS trace the initial temperature while H2CS traces 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 pre-stellar cores. We find that low-mass protostars are preferentially formed within large cores with radii greater than 20000 au, masses between 2 and 4 M-circle dot temperatures lower than or equal to 15 K, and densities between 6 x 10(4) and 2.5 x 10(5) part cm(-3), corresponding to free-fall times between 100 and 200 kyr.