Desorption from interstellar ices

Roberts, J. F.; Rawlings, J. M. C.; Viti, S.; Williams, D. A.

doi:10.1111/j.1365-2966.2007.12402.x

Cited by 120 publications

(165 citation statements)

References 36 publications

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“…However, given the high densities involved in the hot environments modelled in this paper, and since nonthermal desorption mechanisms and their efficiencies are not determined very well experimentally (e.g. see Roberts et al 2007), adjusting the final percentage of freeze out by reducing the efficiency of the sticking to the grains (via the f r parameter) is sufficient, therefore avoiding extra free parameters. On the other hand, having Phase I as a separate step calculation allows that the initial molecular fractional abundances used in Phase II calculations are computed by a real time dependence of the chemical evolution of gas-dust interaction processes, i.e.…”

Section: Chemical Modelmentioning

confidence: 99%

Modelling the sulphur chemistry evolution in Orion KL

Esplugues

Viti

Goicoechea

et al. 2014

A&A

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Context. We present a study of the sulphur chemistry evolution in the region Orion KL along the gas and grain phases of the cloud. Aims. Our aim is to investigate the processes that dominate the sulphur chemistry in Orion KL and to determine how physical and chemical parameters, such as the final mass of the star and the initial elemental abundances, influence the evolution of the hot core and of the surrounding outflows and shocked gas (the plateau). Methods. We independently modelled the chemistry evolution of the hot core and the plateau using the time-dependent gas-grain model UCL_CHEM and considering two different phase calculations. Phase I starts with the collapsing cloud and the depletion of atoms and molecules onto grain surfaces. Phase II starts when a central protostar is formed and the evaporation from grains takes place. We show how the stellar mass, the gas density, the gas depletion efficiency, the initial sulphur abundance, the shocked gas temperature, and the different chemical paths on the grains leading to different reservoirs of sulphur on the mantles affect sulphurbearing molecules at different evolutionary stages for both components. We also compare the predicted column densities with those inferred from observations of the species SO, SO 2 , CS, OCS, H 2 S, and H 2 CS.Results. The models that reproduce the observations of the largest number of sulphur-bearing species in both components are those with an initial sulphur abundance of 0.1 times the sulphur solar abundance (0.1 S ) and a density of at least n H = 5 × 10 6 cm −3 in the shocked gas region. Conclusions. We conclude that most of the sulphur atoms were ionised during Phase I, consistent with an inhomogeneous and clumpy region where the UV interstellar radiation penetrates and leading to sulphur ionisation. We also conclude that the main sulphur reservoir on the ice mantles was H 2 S. In addition, we deduce that a chemical transition currently takes place in the plateau shocked gas, where SO and SO 2 gas-phase formation reactions change from being dominated by O 2 to being dominated by OH.

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Section: Chemical Modelmentioning

confidence: 99%

Modelling the sulphur chemistry evolution in Orion KL

Esplugues

Viti

Goicoechea

et al. 2014

A&A

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“…Depending on the velocity of the jet-induced shock, dust grains can be either partially or completely destroyed by sputtering, grain-grain collisions, and shattering (e.g., Jones et al 1994;Van Loo et al 2013). Moreover, the processing by both UV photons and cosmic rays can cause non-thermal desorption of volatile species from the icy grain mantles into the gas phase (e.g., Hartquist & Williams 1990;Roberts et al 2007). However, it is also possible that higher values of β are actually caused by the growth of icy mantles on dust grains (e.g., Schnee et al 2010a, and references therein), but this seems to contradict the chemical features discussed earlier.…”

Section: Dust Propertiesmentioning

confidence: 99%

SABOCA 350-μm and LABOCA 870-μm dust continuum imaging of IRAS 05399-0121: mapping the dust properties of a pre- and protostellar core system

Miettinen

Offner

2013

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Context. Thermal emission from dust provides a valuable tool for determining important physical properties of the dense structures within molecular clouds. Aims. We attempt to map the distributions of dust temperature and H 2 column density of IRAS 05399-0121/SMM 1, which is a dense double-core system in Orion B9. We also search for substructures within the cores through high-resolution submillimetre imaging. Methods. The source was mapped with APEX/SABOCA at 350 μm. We combined these data with our previous LABOCA 870-μm data. The spatial resolution of the new SABOCA image, ∼3400 AU, is about 2.6 times better than provided by LABOCA, and is therefore well-suited to our purposes. We also make use of the Spitzer infrared observations to characterise the star-formation activity in the source. Results. The filamentary source remains a double-core system on the 3400 AU scale probed here, and the projected separation between IRAS 05399 and SMM 1 is 0.14 pc. The temperature map reveals warm spots towards IRAS 05399 and the southeastern tip of the source. Both IRAS 05399 and SMM 1 stand out as peaks in the column density map. A simple analysis suggests that the density profile has the form ∼r −(2.3 +2.2 −0.9 ) , as determined at the position of SMM 1. The broadband spectral energy distribution of IRAS 05399 suggests that it is near the Stage 0/I borderline. A visual inspection of the Spitzer/IRAC images provides hints of a quadrupolar-like jet morphology around IRAS 05399, supporting the possibility that it is a binary system. Conclusions. The source splitting into two subcores along the long axis can be explained by cylindrical Jeans-type fragmentation, but the steepness of the density profile is shallower than what is expected for an isothermal cylinder. The difference between the evolutionary stages of IRAS 05399 (protostellar) and SMM 1 (starless) suggests that the former has experienced a phase of rapid mass accretion, supported by the very long outflow it drives. The protostellar jet from IRAS 05399 might have influenced the nearby core SMM 1. In particular, the temperature map features are likely to be imprints of protostellar or shock heating, while external heating could be provided by the nearby high-mass star-forming region NGC 2024.

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“…The sticking coefficient used by previous authors (i.e. Willacy & Williams 1993;Nejad & Wagenblast 1999;Roberts et al 2007;Aikawa et al 1997;Turner 1998b;Willacy & Millar 1998;Brown & Charnley 1990) for heavy species is 0.1 to 1, usually around 0.33, and that for light species is 0 to 1. We took an approximate average path with S i = 0.33 for all heavy species and 0.1 for hydrogen atoms and H 2 molecules.…”

Section: Molecule Accretion Onto Grainsmentioning

confidence: 99%

Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores

Kalvāns¹,

Shmeld²

2010

A&A

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Context. The abundances of many observed compounds in interstellar molecular clouds still lack an explanation, despite extensive research that includes both gas and solid (dust-grain surface) phase reactions. Aims. We aim to qualitatively prove the idea that a hydrogen-poor subsurface chemistry on interstellar grains is responsible for at least some of these chemical "anomalies". This chemistry develops in the icy mantles when photodissociation reactions in the mantle release free hydrogen, which escapes the mantle via diffusion. This results in serious alterations of the chemical composition of the mantle because pores in the mantle provide surfaces for reactions in the new, hydrogen-poor environment.Methods. We present a simple kinetic model, using existing astrochemical reaction databases. Gas phase, surface and subsurface pore reactions are included, as are physical transformations of molecules. Results. Our model produces significantly higher abundances for various oxidized species than most other models. We also obtain quite good results for some individual species that have adequate reaction network. Thus, we consider that the hydrogen-poor mantle chemistry may indeed play a role in the chemical evolution of molecular clouds. Conclusions. The significance of outward hydrogen diffusion has to be proved by further research. A huge number of solid phase reactions between many oxidized species is essential to obtain good, quantitative modeling results for a comparison with observations. We speculate that a variety of unobservable hydrogen-poor sulfur oxoacid derivatives may be responsible for the "disappearance" of sulfur in dark cloud cores.

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Desorption from interstellar ices

Cited by 120 publications

References 36 publications

Modelling the sulphur chemistry evolution in Orion KL

Modelling the sulphur chemistry evolution in Orion KL

SABOCA 350-μm and LABOCA 870-μm dust continuum imaging of IRAS 05399-0121: mapping the dust properties of a pre- and protostellar core system

Subsurface chemistry of mantles of interstellar dust grains in dark molecular cores

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