Chemulator: Fast, accurate thermochemistry for dynamical models through emulation

Abstract

Chemical modelling serves two purposes in dynamical models: accounting for the effect of microphysics on the dynamics and providing observable signatures. Ideally, the former must be done as part of the hydrodynamic simulation but this comes with a prohibitive computational cost which leads to many simplifications being used in practice. To produce a statistical emulator that replicates a full chemical model capable of solving the temperature and abundances of a gas through time. This emulator should suffer only a minor loss of accuracy over including a full chemical solver in a dynamical model but would have a fraction of the computational cost. The gas-grain chemical code UCLCHEM was updated to include heating and cooling processes and a large dataset of model outputs from possible starting conditions was produced. A neural network was then trained to map directly from inputs to outputs. Chemulator replicates the outputs of UCLCHEM with an overall mean squared error (MSE) of 0.0002 for a single time step of 1000 yr and is shown to be stable over 1000 iterations with an MSE of 0.003 the log scaled temperature after one time step and 0.006 after 1000 time steps. Chemulator was found to be approximately 50,000 times faster than the time dependent model it emulates but can introduce a significant error to some models.

16 pages, 12 figures, accepted for publication in A&A

References in corpus (13)

• Simulating the formation of molecular clouds. I. Slow formation by gravitational collapse from static initial conditions
• A chemical model for the atmosphere of hot Jupiters
• [CII] 158$\mu$m Emission and Metallicity in PDRs
• CO Depletion in Protoplanetary Disks: A Unified Picture Combining Physical Sequestration and Chemical Processing
• UCLCHEM: A Gas-Grain Chemical Code
• Radiative cooling rates, ion fractions, molecule abundances and line emissivities including self-shielding and both local and metagalactic radiation fields
• Convergence of the critical cooling rate for protoplanetary disk fragmentation achieved; the key role of numerical dissipation of angular momentum
• The first multi-dimensional view of mass loss from externally FUV irradiated protoplanetary discs
• The chemistry of protoplanetary fragments formed via gravitational instabilities
• Grand challenges in protoplanetary disc modelling
• The growth of H II regions around massive stars: the role of metallicity and dust
• Modelling the ArH${}^{+}$ emission from the Crab Nebula
• Modelling thermochemical processes in protoplanetary disks I: numerical methods

Cited by in corpus (1)

• Using Statistical Emulation and Knowledge of Grain-Surface Diffusion for Bayesian Inference of Reaction Rate Parameters: An Application to a Glycine Network