Chemical Modelling of Young Stellar Objects, I. Method and Benchmarks

Abstract

Upcoming facilities such as the Herschel Space Observatory or ALMA will deliver a wealth of molecular line observations of young stellar objects (YSOs). Based on line fluxes, chemical abundances can then be estimated by radiative transfer calculations. To derive physical properties from abundances, the chemical network needs to be modeled and fitted to the observations. This modeling process is however computationally exceedingly demanding, particularly if in addition to density and temperature, far UV (FUV) irradiation, X-rays, and multi-dimensional geometry have to be considered. We develop a fast tool, suitable for various applications of chemical modeling in YSOs. A grid of the chemical composition of the gas having a density, temperature, FUV irradiation and X-ray flux is pre-calculated as a function of time. A specific interpolation approach is developed to reduce the database to a feasible size. Published models of AFGL 2591 are used to verify the accuracy of the method. A second benchmark test is carried out for FUV sensitive molecules. The novel method for chemical modeling is more than 250,000 times faster than direct modeling and agrees within a mean factor of 1.35. The tool is distributed for public use. In the course of devloping the method, the chemical evolution is explored: We find that X-ray chemistry in envelopes of YSOs can be reproduced by means of an enhanced cosmic-ray ionization rate. We further find that the abundance of CH+ in low-density gas with high ionization can be enhanced by the recombination of doubly ionized carbon (C++) and suggest a new value for the initial abundance of the main sulphur carrier in the hot-core.

Accepted by ApJS. 24 pages, 15 figures. A version with higher resolution images is available from http://www.astro.phys.ethz.ch/staff/simonbr/papgridI.pdf . Online data available at http://www.astro.phys.ethz.ch/chemgrid.html . Second paper of this series of papers available at arXiv:0906.0588

References in corpus (33)

• Structure of Stationary Photodissociation Fronts
• Diagnostics of irradiated gas in galaxy nuclei. I: A Far-ultraviolet and X-ray dominated region code
• Physical structure and CO abundance of low-mass protostellar envelopes
• Polycylcic Aromatic Hydrocarbons (PAH's) in dense cloud chemistry
• Structure and Evolution of the Envelopes of Deeply Embedded Massive Young Stars
• The evolution of X-ray emission in young stars
• Photoprocesses in protoplanetary disks
• Molecular Evolution and Star Formation: From Prestellar Cores to Protostellar Cores
• Evolution of Chemistry and Molecular Line Profile during Protostellar Collapse
• Resetting chemical clocks of hot cores based on S-bearing molecules
• The effect of uncertainties on chemical models of dark clouds
• Low sulfur depletion in the Horsehead PDR
• Chemistry as a probe of the structures and evolution of massive star forming regions
• The Impact of the Massive Young Star GL 2591 on its Circumstellar Material: Temperature, Density and Velocity Structure
• Sulphur chemistry in the envelopes of massive young stars
• X-ray chemistry in envelopes around young stellar objects
• Chemistry in Protoplanetary Disks: A Sensitivity Analysis
• Physical-chemical modeling of the low-mass protostar IRAS 16293-2422
• Water emission in NGC1333-IRAS4: The physical structure of the envelope
• Estimation and reduction of the uncertainties in chemical models: Application to hot core chemistry
• Chemistry in Disks. IX. Observations and modeling of HCO+ and DCO+ in DM Tau
• Turbulent transport and its effect on the dead zone in protoplanetary discs
• Atomic Diagnostics of X-ray Irradiated Protoplanetary Disks
• A New Exact Method for Line Radiative Transfer
• The excitation of water in the S140 photon dominated region
• Influence of UV radiation from a massive YSO on the chemistry of its envelope
• Tracing high energy radiation with molecular lines near deeply embedded protostars
• Energetic radiation and the sulfur chemistry of protostellar envelopes: Submillimeter interferometry of AFGL 2591
• Water destruction by X-rays in young stellar objects
• Astrochemical confirmation of the rapid evolution of massive YSOs and explanation for the inferred ages of hot cores
• Determining the cosmic ray ionization rate in dynamically evolving clouds
• The Effects of Doubly Ionized Chemistry on SH+ and S^+2 Abundances in X-ray Dominated Regions
• Star and Planet Formation with ALMA: an Overview

Cited by in corpus (49)

• Interstellar water chemistry: from laboratory to observations
• On the theory of disc photoevaporation
• The warm gas atmosphere of the HD 100546 disk seen by Herschel (Evidence of a gas-rich, carbon-poor atmosphere?)
• Volatile carbon locking and release in protoplanetary disks. A study of TW Hya and HD 100546
• Photodissociation and X-Ray Dominated Regions
• Different dust and gas radial extents in protoplanetary disks: consistent models of grain growth and CO emission
• The chemical history of molecules in circumstellar disks. II. Gas-phase species
• The interstellar gas-phase chemistry of HCN and HNC
• CO destruction in protoplanetary disk midplanes: inside versus outside the CO snow surface
• Modelling Herschel observations of hot molecular gas emission from embedded low-mass protostars
• Excited OH+, H2O+, and H3O+ in NGC 4418 and Arp 220
• Robustness of N2H+ as tracer of the CO snowline
• Water vapor distribution in protoplanetary disks
• Consistent dust and gas models for protoplanetary disks III. Models for selected objects from the FP7 DIANA project
• Herschel-PACS observation of the 10 Myr old T Tauri disk TW Hya: Constraining the disk gas mass
• Global Hydromagnetic Simulations of Protoplanetary Disks with Stellar Irradiation and Simplified Thermochemistry
• Survey of cold water lines in protoplanetary disks: indications of systematic volatile depletion
• A complete model of CH+ rotational excitation including radiative and chemical pumping processes
• The TW Hya Rosetta Stone Project III: Resolving the Gaseous Thermal Profile of the Disk
• Grand challenges in protoplanetary disc modelling
• Chemically tracing the water snowline in protoplanetary disks with HCO${}^{+}$
• Gas temperature structure across transition disk cavities
• [C II] emission from galactic nuclei in the presence of X-rays
• WISH VI. Constraints on UV and X-ray irradiation from a survey of hydrides in low- to high-mass YSOs
• Reducing the complexity of chemical networks via interpretable autoencoders
• X-ray induced chemistry of water and related molecules in low-mass protostellar envelopes
• Outflowing OH${}^{+}$ in Markarian 231: the ionization rate of the molecular gas
• The KOSMA-$\tau$ PDR Model -- I. Recent updates to the numerical model of photo-dissociated regions
• Exploring HNC and HCN line emission as probes of the protoplanetary disk temperature
• The onset of energetic particle irradiation in Class 0 protostars
• Chemical complexity in astrophysical simulations: optimization and reduction techniques
• Machine learning-accelerated chemistry modeling of protoplanetary disks
• The warm CO gas along the UV-heated outflow cavity walls: a possible interpretation for the Herschel/PACS CO spectra of embedded YSOs
• Gap Opening and Inner Disk Structure in the Strongly Accreting Transition Disk of DM Tau
• HST UV Spectroscopy of the Planet-Hosting T Tauri Star PDS 70
• The HIFI spectral survey of AFGL2591 (CHESS). I. Highly excited linear rotor molecules in the high-mass protostellar envelope
• Using HCO${}^{+}$ isotopologues as tracers of gas depletion in protoplanetary disk gaps
• Neutral and Ionized Hydrides in Star-forming Regions -- Observations with Herschel/HIFI
• The HIFI spectral survey of AFGL 2591 (CHESS). III. Chemical structure of the protostellar envelope
• A PDR model for the FIR mid-$J$ CO ladder with universal rotational temperature in star forming region
• Signatures of UV radiation in low-mass protostars I. Origin of HCN and CN emission in the Serpens Main region
• Modelling thermochemical processes in protoplanetary disks I: numerical methods
• Photoevaporation Can Reproduce Extended ${\mathrm{H}}_2$ Emission from Protoplanetary Disks Imaged by JWST MIRI
• Dancing on the Grain: Variety of CO and its isotopologue fluxes as a result of surface chemistry and T Tauri disk properties
• On the pumping of the CS($v=0$) masers in W51 e2e
• Zooming into the water snowline: high resolution water observations of the HL Tau disk
• Hunting for methanol in the water rich, planet forming disk around HL Tau
• Chemical history of molecules in circumstellar disks
• Chandra X-ray Observations of V830 Tau: A T Tauri Star Hosting an Evanescent Planet