Shock Chemistry in the Young Bipolar Outflow L1157

Bachiller, R.; Gutiérrez, Manuel Pérez

doi:10.1086/310877

Cited by 307 publications

(380 citation statements)

References 23 publications

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“…Several works (e.g., Irvine et al 1987;Tafalla et al 2010;Busquet et al 2011;Tafalla & Hacar 2013) report, from studies in different star-forming regions, an HCO + abundance in the range 1−9 × 10 −9 , with no large enhancements when comparing the outflow gas with the dense core. In contrast, the abundance of SiO has been found to vary by several orders of magnitude, with values ranging from 10 −12 to 10 −7 (e.g., Ziurys et al 1989;Bachiller & Perez Gutierrez 1997;Garay et al 1998;Codella et al 2005;Nisini et al 2007). For our sources, we refrained from assuming a given SiO abundance and estimated it using two approaches.…”

Section: Derivation Of Outflow Parametersmentioning

confidence: 99%

Evolution and excitation conditions of outflows in high-mass star-forming regions

Sánchez-Monge

López-Sepulcre

Cesaroni

et al. 2013

A&A

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Context. Theoretical models suggest that massive stars form via disk-mediated accretion in a similar fashion to low-mass stars. In this scenario, bipolar outflows ejected along the disk axis play a fundamental role, and their study can help characterize the different evolutionary stages involved in the formation of a high-mass star. A recent study toward massive molecular outflows has revealed a decrease in the SiO line intensity as the object evolves. Aims. The present study aims to characterize the variation of the molecular outflow properties with time and to study the SiO excitation conditions in outflows associated with high-mass young stellar objects (YSOs). Methods. We used the IRAM 30-m telescope on Pico Veleta (Spain) to map 14 high-mass star-forming regions in the SiO (2-1), SiO (5-4), and HCO + (1-0) lines, which trace the molecular outflow emission. The FTS backend, covering a total frequency range of ∼15 GHz, allowed us to simultaneously map several dense gas (e.g., N 2 H + , C 2 H, NH 2 D, H 13 CN) and hot-core (CH 3 CN) tracers. We used the Hi-GAL data to improve the previous spectral energy distributions and obtained a more accurate dust envelope mass and bolometric luminosity for each source. We calculated the luminosity-to-mass ratio, which is believed to be a good indicator of the evolutionary stage of the YSO. Results. We detect SiO and HCO + outflow emission in all fourteen sources and bipolar structures in six of them. The outflow parameters are similar to those found toward other massive YSOs with luminosities 10 3 −10 4 L . We find an increase in the HCO + outflow energetics as the object evolves, and a decrease in the SiO abundance with time from 10 −8 to 10 −9 . The SiO (5-4) to (2-1) line ratio is found to be low at the ambient gas velocity, and increases as we move to red-/blue-shifted velocities, indicating that the excitation conditions of the SiO change with the velocity of the gas. In particular, the high-velocity SiO gas component seems to arise from regions with higher densities and/or temperatures than the SiO emission at the ambient gas velocity. Conclusions. The properties of the SiO and HCO + outflow emission suggest a scenario in which SiO is largely enhanced in the first evolutionary stages, probably owing to strong shocks produced by the protostellar jet. As the object evolves, the power of the jet would decrease and so does the SiO abundance. During this process, however, the material surrounding the protostar would have been been swept up by the jet, and the outflow activity, traced by entrained molecular material (HCO + ), would increase with time.

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Section: Derivation Of Outflow Parametersmentioning

confidence: 99%

Evolution and excitation conditions of outflows in high-mass star-forming regions

Sánchez-Monge

López-Sepulcre

Cesaroni

et al. 2013

A&A

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“…The increase or decrease in the abundances of other species, linked to reaction networks of CS and SO, could also have an effect. Abundances of both species can also be increased by the impact of outflows which processes the gas (e.g., Bachiller & Perez Gutierrez 1997). As outflows are not included we could underestimate the abundances.…”

Section: Cs and Somentioning

confidence: 99%

Modeling the chemical evolution of a collapsing prestellar core in two spatial dimensions

Weeren¹,

Brinch

Hogerheijde³

2009

A&A

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Context. The physical conditions in a collapsing cloud can be traced by observations of molecular lines. To correctly interpret these observations the abundance distributions of the observed species need to be derived. The chemistry in a collapsing molecular cloud is not in a steady state as the density and temperature evolve. We therefore need to follow chemical reactions, both in the gas phase and on dust grains, as well as gas-grain interactions, to predict the abundance distributions. Aims. Our aim is to model the abundances of molecules, in the gas phase and on grain mantles in the form of ice, from prestellar core collapse to disk formation. We want to investigate the need for grain surface reactions and compare our results with observed abundances, column densities, and ice-mantle compositions. Methods. We use a 2-dimensional hydrodynamical simulation as a physical model from which we take the density, temperature, and the flow of the gas. Trace particles, moving along with the gas, are used to follow the chemistry during prestellar core collapse and disk formation. We calculated abundance profiles and column densities for various species. The evolution of these abundances and the composition of ices on grain mantles were compared to observations and we tested the influence of grain surface reactions on the abundances of species. We also investigated the initial abundances to be adopted in more detailed modeling of protoplanetary disks by following the chemical evolution of trace particles accreting onto the disk. Results. Fractional abundances of HCO + , N 2 H + , H 2 CO, HC 3 N, and CH 3 OH from our model with grain surface reactions provide a good match to observations, while abundances of CO, CS, SO, HCN, and HNC show better agreement without grain surface reactions. The observed mantle composition of dust grains is best reproduced when we include surface reactions. The initial chemical abundances to be used for detailed modeling of a protoplanetary disk are found to be different from those in dark interstellar clouds. Ices with a binding energy lower than about 1200 K sublimate before accreting onto the disk, while those with a higher binding energy do not.

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“…After the gravitational collapse of a molecular cloud, the formation of a new star is accompanied by the development of highly supersonic outflows (Bachiller & Pérez-Gutiérrez 1997). The material ejected through these jets collides with the surrounding cloud, compressing and heating the gas, which leads to a drastic alteration of the chemistry because endothermic reactions (or reactions with energy activations barriers) become efficient and dust grains are destroyed.…”

Section: Introductionmentioning

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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Shock Chemistry in the Young Bipolar Outflow L1157

Cited by 307 publications

References 23 publications

Evolution and excitation conditions of outflows in high-mass star-forming regions

Evolution and excitation conditions of outflows in high-mass star-forming regions

Modeling the chemical evolution of a collapsing prestellar core in two spatial dimensions

Modelling the sulphur chemistry evolution in Orion KL

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