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- Suutarinen, A., et al.
(författare)
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CH abundance gradient in TMC-1
- 2011
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 531, s. A121-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. The aim of this study is to examine if the well-known chemical gradient in TMC-1 is reflected in the amount of rudimentaryforms of carbon available in the gas-phase. As a tracer we use the CH radical which is supposed to be well correlated with carbonatoms and simple hydrocarbon ions.Methods. We observed the 9-cm Λ-doubling lines of CH along the dense filament of TMC-1. The CH column densities were comparedwith the total H2 column densities derived using the 2MASS NIR data and previously published SCUBA maps and with OH columndensities derived using previous observations with Effelsberg. We also modelled the chemical evolution of TMC-1 adopting physicalconditions typical of dark clouds using the UMIST Database for Astrochemistry gas-phase reaction network to aid the interpretationof the observed OH/CH abundance ratios.Results. The CH column density has a clear peak in the vicinity of the cyanopolyyne maximum of TMC-1. The fractional CHabundance relative to H2 increases steadily from the northwestern end of the filament where it lies around 1.0 × 10−8, to the southeastwhere it reaches a value of 2.0 × 10−8. The OH and CH column densities are well correlated, and we obtained OH/CH abundanceratios of ∼16–20. These values are clearly larger than what has been measured recently in diffuse interstellar gas and is likely to berelated to C to CO conversion at higher densities. The good correlation between CH and OH can be explained by similar productionand destruction pathways. We suggest that the observed CH and OH abundance gradients are mainly due to enhanced abundances ina low-density envelope which becomes more prominent in the southeastern part and seems to continue beyond the dense filament.Conclusions. An extensive envelope probably signifies an early stage of dynamical evolution, and conforms with the detection of alarge CH abundance in the southeastern part of the cloud. The implied presence of other simple forms of carbon in the gas phase provides a natural explanation for the observation of "early-type" molecules in this region.
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| 3. |
- Perotti, G., et al.
(författare)
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Linking ice and gas in the λ Orionis Barnard 35A cloud
- 2021
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 650
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Tidskriftsartikel (refereegranskat)abstract
- Context. Dust grains play an important role in the synthesis of molecules in the interstellar medium, from the simplest species, such as H2, to complex organic molecules. How some of these solid-state molecules are converted into gas-phase species is still a matter of debate. Aims. Our aim is to directly compare ice and gas abundances of methanol (CH3OH) and carbon monoxide (CO) obtained from near-infrared (2.5-5 μm) and millimetre (1.3 mm) observations and to investigate the relationship between ice, dust, and gas in low-mass protostellar envelopes. Methods. We present Submillimeter Array (SMA) and Atacama Pathfinder EXperiment (APEX) observations of gas-phase CH3OH (JK = 5K-4K), 13CO, and C18O (J = 2-1) towards the multiple protostellar system IRAS 05417+0907, which is located in the B35A cloud, λ Orionis region. We use archival IRAM 30 m data and AKARI H2O, CO, and CH3OH ice observations towards the same target to compare ice and gas abundances and directly calculate CH3OH and CO gas-to-ice ratios. Results. The CO isotopologue emissions are extended, whereas the CH3OH emission is compact and traces the giant molecular outflow emanating from IRAS 05417+0907. A discrepancy between sub-millimetre dust emission and H2O ice column density is found for B35A-4 and B35A-5, similar to what has previously been reported. B35A-2 and B35A-3 are located where the sub-millimetre dust emission peaks and show H2O column densities lower than that of B35A-4. Conclusions. The difference between the sub-millimetre continuum emission and the infrared H2O ice observations suggests that the distributions of dust and H2O ice differ around the young stellar objects in this dense cloud. The reason for this may be that the four sources are located in different environments resolved by the interferometric observations: B35A-2, B35A-3, and, in particular, B35A-5 are situated in a shocked region that is plausibly affected by sputtering and heating, which in turn impacts the sub-millimetre dust emission pattern, while B35A-4 is situated in a more quiescent part of the cloud. Gas and ice maps are essential for connecting small-scale variations in the ice composition with the large-scale astrophysical phenomena probed by gas observations.
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