A 330-360 GHz spectral survey of G 34.3+0.15. 
I. Data and physical analysis

Macdonald, G. H.; Gibb, A. G.; Habing, R. J.; Millar, T. J.

doi:10.1051/aas:1996249

Cited by 109 publications

(95 citation statements)

References 18 publications

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“…Observations of hot cores with interferometers are represented by blue diamonds: G34.3+0.15 by MacDonald et al (1996), G19.61-0.23 by Qin et al (2010), Orion KL, G29.96 by Beuther et al (2009), and G47.47+0.05 by Remijan et al (2004). The red curves report the predictions of the methyl formate to methanol abundance ratio appropriate to the hot corinos case by Garrod et al (2008, their Fig.…”

Section: Introductionmentioning

confidence: 90%

Multilayer modeling of porous grain surface chemistry

Taquet

Ceccarelli

Kahane

2012

A&A

145

157

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Context. Mantles of iced water mixed with carbon monoxyde, formaldehyde, and methanol are formed during the so-called prestellar core phase. In addition, radicals are also thought to be formed on the grain surfaces, and to react to form complex organic molecules later on, during the so-called warm-up phase of the protostellar evolution. Aims. We aim to study the formation of the grain mantles during the prestellar core phase and the abundance of formaldehyde, methanol, and radicals trapped in them. Methods. We have developed a macrosopic statistic multilayer model that follows the formation of grain mantles with time and that includes two effects that may increase the number of radicals trapped in the mantles: i) during the mantle formation, only the surface layer is chemically active and not the entire bulk; and ii) the porous structure of grains allows the trapping reactive particles. The model considers a network of H, O, and CO forming neutral species such as water, CO, formaldehyde, and methanol, plus several radicals. We ran a large grid of models to study the impact of the mantle multilayer nature and grain porous structure. In addition, we explored how the uncertainty of other key parameters influences the mantle composition. Results. Our model predicts relatively high abundances of radicals, especially of HCO and CH 3 O (10 −9 −10 −7 ). In addition, the multilayer approach enables us to follow the chemical differentiation within the grain mantle, showing that the mantles are far from being uniform. For example, methanol is mostly present in the outer layers of the mantles, whereas CO and other reactive species are trapped in the inner layers. The overall mantle composition depends on the density and age of the prestellar core as well as on some microscopic parameters, such as the diffusion energy and the hydrogenation reactions activation energy. Comparison with observations allows us to constrain the value of the last two parameters (0.5-0.65 and 1500 K, respectively) and provide some indications on the physical conditions during the formation of the ices.

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Section: Introductionmentioning

confidence: 90%

Multilayer modeling of porous grain surface chemistry

Taquet

Ceccarelli

Kahane

2012

A&A

145

157

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“…Figure 1 shows the HNCO abundance along with that of OCN for a range assumed rate coefficients for reaction c. For a rate coefficient of 10 −18 cm 3 s −1 and above it is possible to achieve HNCO abundances within the observed range of 1.4 ×10 −10 to 5.4 ×10 −8 (MacDonald et al 1996;Bisschop et al 2007). Equation (2) implies that for the ∼4500 K barrier which laboratory data (NIST) infer for this reaction, temperatures above 277 K are required to reach this value of the rate coefficient for reaction c. Alternatively for this reaction to be effective at a gas temperature of 10 K, the barrier would have to be less than ∼165 K, much lower than measurements indicate.…”

Section: Gas Phase Formation Of Hnco In Dark Cloudsmentioning

confidence: 95%

The abundance of HNCO and its use as a diagnostic of environment

Tideswell¹,

Fuller²,

Millar

et al. 2010

A&A

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Aims. We aim to investigate the chemistry and gas phase abundance of HNCO and the variation of the HNCO/CS abundance ratio as a diagnostic of the physics and chemistry in regions of massive star formation. Methods. A numerical-chemical model has been developed which self-consistently follows the chemical evolution of a hot core. The model comprises of two distinct stages. The first stage follows the isothermal, modified free-fall collapse of a molecular dark cloud. This is immediately followed by an increase in temperature which represents the switch on of a central massive star and the subsequent evolution of the chemistry in a hot, dense gas cloud (the hot core). During the collapse phase, gas species are allowed to accrete on to grain surfaces where they can participate in further reactions. During the hot core phase surface species thermally desorb back in to the ambient gas and further chemical evolution takes place. For comparison, the chemical network was also used to model a simple dark cloud and photodissociation regions. Results. Our investigation reveals that HNCO is inefficiently formed when only gas-phase formation pathways are considered in the chemical network with reaction rates consistent with existing laboratory data. This is particularly true at low temperatures but also in regions with temperatures up to ∼200 K. Using currently measured gas phase reaction rates, obtaining the observed HNCO abundances requires its formation on grain surfaces -similar to other "hot core" species such as CH 3 OH. However our model shows that the gas phase HNCO in hot cores is not a simple direct product of the evaporation of grain mantles. We also show that the HNCO/CS abundance ratio varies as a function of time in hot cores and can match the range of values observed. This ratio is not unambiguously related to the ambient UV field as been suggested -our results are inconsistent with the hypothesis of Martín et al. (2008, ApJ, 678, 245). In addition, our results show that this ratio is extremely sensitive to the initial sulphur abundance. We find that the ratio grows monotonically with time with an absolute value which scales approximately linearly with the S abundance at early times.

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“…They have covered the whole range of frequencies reachable from the ground, from the 3 mm range observed with IRAM, SEST, NRAO, or JCMT to the submillimeter windows observable with the CSO and JCMT (MacDonald et al 1996;Schilke et al 1997;Helmich & van Dishoeck 1997;Nummelin et al 1998;Thompson & MacDonald 1999;Kim et al 2000;Nummelin et al 2000;Lee et al 2001;Schilke et al 2001;White et al 2003;Comito et al 2005;Kim et al 2006;Belloche et al 2007;Olofsson et al 2007;Tercero et al 2010). The line densities usually range from 10 to 20 lines per GHz, i.e.…”

Section: Comparison With Previous Surveysmentioning

confidence: 99%

TIMASSS: the IRAS 16293-2422 millimeter and submillimeter spectral survey

Caux

Kahane

Castets

et al. 2011

A&A

164

220

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Context. Unbiased spectral surveys are powerful tools to study the chemistry and the physics of star forming regions, because they can provide a complete census of the molecular content and the observed lines probe the physical structure of the source. Aims. While unbiased surveys at the millimeter and sub-millimeter wavelengths observable from ground-based telescopes have previously been performed towards several high mass protostars, very little exists on low mass protostars, which are believed to resemble our own Sun's progenitor. To help fill up this gap in our understanding, we carried out a complete spectral survey of the bands at 3, 2, 1, and 0.9 mm towards the solar type protostar IRAS 16293-2422. Methods. The observations covered a range of about 200 GHz and were obtained with the IRAM-30 m and JCMT-15 m telescopes during about 300 h of observations. Particular attention was devoted to the inter-calibration of the acquired spectra with previous observations. All the lines detected with more than 3σ confidence-interval certainty and free from obvious blending effects were fitted with Gaussians to estimate their basic kinematic properties. Results. More than 4000 lines were detected (with σ ≥ 3) and identified, yielding a line density of approximatively 20 lines per GHz, comparable to previous surveys in massive hot cores. The vast majority (about two-thirds) of the lines are weak and produced by complex organic molecules. The analysis of the profiles of more than 1000 lines belonging to 70 species firmly establishes the presence of two distinct velocity components associated with the two objects, A and B, forming the IRAS 16293-2422 binary system. In the source A, the line widths of several species increase with the upper level energy of the transition, a behavior compatible with gas infalling towards a ∼1 M object. The source B, which does not show this effect, might have a much lower central mass of ∼0.1 M . The difference in the rest velocities of both objects is consistent with the hypothesis that the source B rotates around the source A. Conclusions. This spectral survey, although obtained with single-dish telescopes at a low spatial resolution, allows us to separate the emission from two different components, thanks to the large number of lines detected. The data of the survey are public and can be retrieved on the TIMASSS web site .

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A 330-360 GHz spectral survey of G 34.3+0.15. I. Data and physical analysis

Cited by 109 publications

References 18 publications

Multilayer modeling of porous grain surface chemistry

Multilayer modeling of porous grain surface chemistry

The abundance of HNCO and its use as a diagnostic of environment

TIMASSS: the IRAS 16293-2422 millimeter and submillimeter spectral survey

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