2 research outputs found
Chemical post-processing of magneto-hydrodynamical simulations of star-forming regions: robustness and pitfalls
A common approach to model complex chemistry in numerical simulations is via
post-processing of existing magneto-hydrodynamic simulations, relying on
computing the evolution of chemistry over the dynamic history of a subset of
particles from within the raw simulation. Here, we validate such a technique,
assessing its ability to recover the abundances of chemical species, using the
chemistry package KROME. We also assess, for the first time, the importance of
the main free input parameters, by means of a direct comparison with a
self-consistent state-of-the-art simulation in which chemistry was directly
coupled to hydrodynamics. We have found that the post-processing is highly
reliable, with an accuracy at the percent level, even when the most relaxed
input parameters are employed. In particular, our results show that the number
of particles used does not affect significantly the average properties,
although it suppresses the appearance of possibly important spatial features.
On the other hand, the choice of the integration time-step plays a crucial
role. Longer integration time-steps can produce large errors, as the
post-processing solution will be forced towards chemical equilibrium, a
condition that does not always necessarily apply. When the interpolation-based
reconstruction of chemical properties is performed, the errors further increase
up to a factor of . Concluding, our results suggest that this technique
is extremely useful when exploring the relative quantitative effect of
different chemical parameters and/or networks, without the need of re-running
simulations multiple times, but some care should be taken in the choice of
particles sub-sample and integration time-step.Comment: 11 pages, 6 figures, 3 table
The GRETOBAPE gas-phase reaction network: the importance of being exothermic
The gas-phase reaction networks are the backbone of astrochemical models.
However, due to their complexity and non-linear impact on the astrochemical
modeling, they can be the first source of error in the simulations if incorrect
reactions are present. Over time, following the increasing number of species
detected, astrochemists have added new reactions, based on laboratory
experiments and quantum mechanics (QM) computations as well as reactions
inferred by chemical intuition and similarity principle. However, sometimes no
verification of their feasibility in the interstellar conditions, namely their
exothermicity, was performed. In this work, we present a new gas-phase reaction
network, GRETOBAPE, based on the KIDA2014 network and updated with several
reactions, cleaned from endothermic reactions not explicitly recognized as
such. To this end, we characterized all the species in the GRETOBAPE network
with accurate QM calculations. We found that 5% of the reactions in the
original network are endothermic although most of them are reported as
barrierless. The reaction network of Si-bearing species is the most impacted by
the endothermicity cleaning process. We also produced a cleaned reduced
network, GRETOBAPE-red, to be used to simulate astrochemical situations where
only C-, O-, N- and S- bearing species with less than 6 atoms are needed.
Finally, the new GRETOBAPE network, its reduced version, as well as the
database with all the molecular properties are made publicly available. The
species properties database can be used in the future to test the feasibility
of possibly new reactions.Comment: ApJS submitte