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.
