Modelling and Monitoring a Manipulation Environment

Hasegawa, Tsutomu

doi:10.9746/sicetr1965.17.589

Cited by 36 publications

(45 citation statements)

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“…The net rate of change at the surface depends on adsorption, desorption and also on chemical reactions (see Ruaud et al 2016). We note that our approach slightly differs from the one originally proposed by Hasegawa & Herbst (1993), in that in our formulation, a molecule lost at the surface is immediately replaced by transfer of a molecule from the mantle to the surface (see also Ruaud et al 2016).…”

Section: General Equationsmentioning

confidence: 93%

A Three-phase Approach to Grain Surface Chemistry in Protoplanetary Disks: Gas, Ice Surfaces, and Ice Mantles of Dust Grains

Ruaud

Gorti

2019

ApJ

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We study the effects of grain surface reactions on the chemistry of protoplanetary disks where gas, ice surface layers and icy mantles of dust grains are considered as three distinct phases. Gas phase and grain surface chemistry is found to be mainly driven by photo-reactions and dust temperature gradients. The icy disk interior has three distinct chemical regions: (i) the inner midplane with low FUV fluxes and warm dust ( 15K) that lead to the formation of complex organic molecules, (ii) the outer midplane with higher FUV from the ISM and cold dust where hydrogenation reactions dominate and, (iii) a molecular layer above the midplane but below the water condensation front where photodissociation of ices affects gas phase compositions. Some common radicals, e.g., CN and C 2 H, exhibit a two-layered vertical structure and are abundant near the CO photodissociation front and near the water condensation front. The 3-phase approximation in general leads to lower vertical column densities than 2-phase models for many gas-phase molecules due to reduced desorption, e.g., H 2 O, CO 2 , HCN and HCOOH decrease by ∼ two orders of magnitude. Finally, we find that many observed gas phase species originate near the water condensation front; photo-processes determine their column densities which do not vary significantly with key disk properties such as mass and dust/gas ratio.

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Section: General Equationsmentioning

confidence: 93%

A Three-phase Approach to Grain Surface Chemistry in Protoplanetary Disks: Gas, Ice Surfaces, and Ice Mantles of Dust Grains

Ruaud

Gorti

2019

ApJ

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“…where m i is the mass of X * i , E i its adsorption energy taken from Hasegawa & Herbst (1993) and Aikawa et al (1996), and T g (z) is the grain temperature. The photodesorption rate of X * i is written…”

Section: Chemical Networkmentioning

confidence: 99%

Models of irradiated molecular shocks

Godard

Forêts

Lesaffre

et al. 2019

A&A

134

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Context. The recent discovery of excited molecules in starburst galaxies observed with ALMA and the Herschel space telescope has highlighted the necessity to understand the relative contributions of radiative and mechanical energies in the formation of molecular lines and explore the conundrum of turbulent gas bred in the wake of galactic outflows. Aims. The goal of the paper is to present a detailed study of the propagation of low velocity (5 to 25 km s −1 ) stationary molecular shocks in environments illuminated by an external ultraviolet (UV) radiation field. In particular, we intend to show how the structure, dynamics, energetics, and chemical properties of shocks are modified by UV photons and to estimate how efficiently shocks can produce line emission. Methods. We implemented several key physico-chemical processes in the Paris-Durham shock code to improve the treatment of the radiative transfer and its impact on dust and gas particles. We propose a new integration algorithm to find the steady-state solutions of magnetohydrodynamics equations in a range of parameters in which the fluid evolves from a supersonic to a subsonic regime. We explored the resulting code over a wide range of physical conditions, which encompass diffuse interstellar clouds and hot and dense photon-dominated regions (PDR). Results. We find that C-type shock conditions cease to exist as soon as G 0 > 0.2 (n H / cm −3 ) 1/2 . Such conditions trigger the emergence of another category of stationary solutions, called C*-type and CJ-type shocks, in which the shocked gas is momentarily subsonic along its trajectory. These solutions are shown to be unique for a given set of physical conditions and correspond to dissipative structures in which the gas is heated up to temperatures comprised between those found in C-type and adiabatic J-type shocks. High temperatures combined with the ambient UV field favour the production or excitation of a few molecular species to the detriment of others, hence leading to specific spectroscopic tracers such as rovibrational lines of H 2 and rotational lines of CH + . Unexpectedly, the rotational lines of CH + may carry as much as several percent of the shock kinetic energy. Conclusions. Ultraviolet photons are found to strongly modify the way the mechanical energy of interstellar shocks is processed and radiated away. In spite of what intuition dictates, a strong external UV radiation field boosts the efficiency of low velocity interstellar shocks in the production of several molecular lines which become evident tracers of turbulent dissipation.

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“…11 for the MWC 480 and LkCa 15 cases) is fed as an input in the pseudo timedependent astrochemical modeling code Nautilus v1.1 ) used in three-phase mode ). This rate-equation gas-grain code -based on Hasegawa et al (1992) and Hasegawa & Herbst (1993) -simulates the time-dependent chemistry of ∼ 1100 species (half in the gas phase and half in solid phase) linked together via more than ∼ 12000 reactions, in the vertical direction at each radius in three different phases: gas, grain surface (top two ice layers on grains), and grain mantle (deeper ice layers on grains). Exchanges in between all the different phases are included: adsorption and desorption processes link the gas and surface phases, and swapping processes link the mantle and surface of grains.…”

Section: Chemical Modelingmentioning

confidence: 99%

“…Exchanges in between all the different phases are included: adsorption and desorption processes link the gas and surface phases, and swapping processes link the mantle and surface of grains. Several desorption mechanisms are considered, thermal desorption (Hasegawa et al 1992), and non thermal ones, such as cosmic-ray induced desorption (Hasegawa & Herbst 1993), photodesorption and chemical desorption (for further details see e.g. Garrod et al 2007;Ruaud et al 2016;Wakelam et al 2016;Le Gal et al 2017).…”

Section: Chemical Modelingmentioning

confidence: 99%

Sulfur Chemistry in Protoplanetary Disks: CS and H₂CS

Gal

Öberg

Loomis

et al. 2019

ApJ

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The nature and abundance of sulfur chemistry in protoplanetary disks (PPDs) may impact the sulfur inventory on young planets and therefore their habitability. PPDs also present an interesting test bed for sulfur chemistry models, since each disk present a diverse set of environments. In this context, we present new sulfur molecule observations in PPDs, and new S-disk chemistry models. With ALMA we observed the CS 5 − 4 rotational transition toward five PPDs (DM Tau, DO Tau, CI Tau, LkCa 15, MWC 480), and the CS 6 − 5 transition toward three PPDs (LkCa 15, MWC 480 and V4046 Sgr). Across this sample, CS displays a range of radial distributions, from centrally peaked, to gaps and rings. We also present the first detection in PPDs of 13 CS 6 − 5 (LkCa 15 and MWC 480), C 34 S 6 − 5 (LkCa 15), and H 2 CS 8 17 − 7 16 , 9 19 − 8 18 and 9 18 − 8 17 (MWC 480) transitions. Using LTE models to constrain column densities and excitation temperatures, we find that either 13 C and 34 S are enhanced in CS, or CS is optically thick despite its relatively low brightness temperature. Additional lines and higher spatial resolution observations are needed to distinguish between these scenarios. Assuming CS is optically thin, CS column density model predictions reproduce the observations within a factor of a few for both MWC 480 and LkCa 15. However, the model underpredicts H 2 CS by 1-2 orders of magnitude. Finally, comparing the H 2 CS/CS ratio observed toward the MWC 480 disk and toward different ISM sources, we find the closest match with prestellar cores. two of the Taurus disks: the Herbig Ae disk MWC 480, and the T Tauri disk LkCa 15. The spectral resolution for these lines was ∼ 975 kHz, i.e. corresponding to a velocity resolution of ∼ 1 km/s. The 12 CS 6 − 5 transition was observed in three execution blocks on January 17, 2016, April 23, 2016 and December 12, 2016. For the first execution block 31 antennas were included and covered baselines from 15 to 331 m. 36 antennas were included for the two other execution blocks, covering baselines from 15 to 463 m and 15 to 650 m, respectively. The first and third blocks used the source J0510+1800 as band-pass and flux calibrators, and the source J0438+3004 as phase calibrator. The second block of execution used the source J0238+1636 as band-pass calibrator, the source J0433+2905 as phase calibrator, and the source J0510+1800 as flux calibrator. The total on-source integration time were 17.6, 12.6 and 20.7 min., respectively.The 13 CS and C 34 S 6−5, and H 2 CS 8 17 −7 16 rotational transitions were observed in a single execution block, on January 17, 2016, with the same calibrator sources as those used for the first and second execution blocks used for 12 CS 6 − 5 (see above) but with 36 antennas and a total on-source integration time of ∼ 19.2 min.

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Modelling and Monitoring a Manipulation Environment

Cited by 36 publications

References 0 publications

A Three-phase Approach to Grain Surface Chemistry in Protoplanetary Disks: Gas, Ice Surfaces, and Ice Mantles of Dust Grains

A Three-phase Approach to Grain Surface Chemistry in Protoplanetary Disks: Gas, Ice Surfaces, and Ice Mantles of Dust Grains

Models of irradiated molecular shocks

Sulfur Chemistry in Protoplanetary Disks: CS and H₂CS

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Modelling and Monitoring a Manipulation Environment

Cited by 36 publications

References 0 publications

A Three-phase Approach to Grain Surface Chemistry in Protoplanetary Disks: Gas, Ice Surfaces, and Ice Mantles of Dust Grains

A Three-phase Approach to Grain Surface Chemistry in Protoplanetary Disks: Gas, Ice Surfaces, and Ice Mantles of Dust Grains

Models of irradiated molecular shocks

Sulfur Chemistry in Protoplanetary Disks: CS and H2CS

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Sulfur Chemistry in Protoplanetary Disks: CS and H₂CS