The Abundance of Carbon Dioxide Ice in the Quiescent Intracloud Medium

Whittet, D. C. B.; Shenoy, S.; Bergin, Edwin A.; Chiar, J. E.; Gerakines, P. A.; Gibb, E. L.; Melnick, Gary J.; Neufeld, David A.

doi:10.1086/509772

Cited by 122 publications

(243 citation statements)

References 57 publications

(91 reference statements)

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“…IR A&A 528, A118 (2011) observations of several interstellar clouds show that the abundance of solid CO 2 , in polar (water-rich) icy mantles, is in the range 10-25% with respect to water ice, although some sources, e.g., AFGL 989 and Elias 18, exhibit an even higher (34-37%) CO 2 abundance, while CO 2 column density in apolar mantles varies strongly, depending critically on the temperature profile along the line of sight (e.g., Gerakines et al 1999;Gibb et al 2004;Boogert et al 2004;Whittet et al 2007;Pontoppidan et al 2008).…”

Section: Introductionmentioning

confidence: 99%

The influence of temperature on the synthesis of molecules on icy grain mantles in dense molecular clouds

Garozzo

Rosa

Kaňuchová

et al. 2011

A&A

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Context. Infrared observations show the presence of icy mantles along the line of sight toward young stellar objects (YSOs), where a temperature gradient is expected and indirectly observed. In this environment, icy mantles are affected by ion and UV irradiation. Laboratory experiments show that molecules are formed after irradiation of icy mixtures. However, most of the experiments done so far have been performed in the temperatures range of 10-20 K. Aims. To extend previous work we irradiated some icy mixtures, namely H 2 O:CO=10:1, H 2 O:CH 4 =4:1, and H 2 O:CO 2 =3:1 at two different temperatures (12 K and 40 or 60 K) to study the effects of temperature on the synthesis of molecules and the decrease in their parent species after ion irradiation. Methods. The experiments were performed in a high-vacuum chamber (P < 10 −7 mbar), where icy samples were irradiated with 30 keV He + ions and analyzed by a FTIR spectrophotometer. Infrared spectra of the samples were recorded after various steps of irradiation. Results. We found that the temperature affects the behavior of the volatile species (i.e., CO and CH 4 ) during irradiation. As a consequence, the production of molecular species is generally more prevalent at 12 K than at either 40 or 60 K, while the decrease in their parent volatile species is faster at high temperature. Conclusions. We conclude that the behavior of each species depends on the value of its sublimation temperature with respect to the temperature of the sample. If this latter is higher than the sublimation temperature of a given species, then the effects of thermal desorption compete with those due to irradiation.

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Section: Introductionmentioning

confidence: 99%

The influence of temperature on the synthesis of molecules on icy grain mantles in dense molecular clouds

Garozzo

Rosa

Kaňuchová

et al. 2011

A&A

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“…3 were the column of total hydrogen rather than of just H 2 , the B and A model results for CO(g) would appear to be more similar. Note also that the two (Whittet et al 2007) with estimated uncertainties; for CO(s) only the minimum value appears. The horizontal lines indicate estimated minimum column densities for detection (see Sect.…”

Section: Resultsmentioning

confidence: 94%

“…The same chemical-dynamical treatment cannot therefore be used realistically to reach fully formed cloud cores of higher extinction (e.g., TMC-1). However, the model results, especially for the ices, can be compared with observations of cores of low extinction in assemblies such as the Taurus cloud (Whittet et al 2007, and references therein). In addition, results for CO(g) can be compared with observed values in diffuse and translucent regions.…”

Section: Hydrodynamical Modelmentioning

confidence: 99%

“…Shown in Fig. 2, the limited data available in the extinction range up to 3.3 come from Whittet et al (2007); Murakawa et al (2000); Teixeira & Emerson (1999), and references therein. Some of these data are merely upper limits, while for CH 4 (s) and CH 3 OH(s), there are to the best of our knowledge not even upper limits in this range.…”

Section: Ice Observationsmentioning

confidence: 99%

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Beyond the pseudo-time-dependent approach: chemical models of dense core precursors

Hassel¹,

Herbst

Bergin

2010

A&A

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Context. Chemical models of dense cloud cores often utilize the so-called pseudo-time-dependent approximation, in which the physical conditions are held fixed and uniform as the chemistry occurs. In this approximation, the initial abundances chosen, which are totally atomic in nature except for molecular hydrogen, are artificial. A more detailed approach to the chemistry of dense cold cores should include the physical evolution during their early stages of formation. Aims. Our major goal is to investigate the initial synthesis of molecular ices and gas-phase molecules as cold molecular gas begins to form behind a shock in the diffuse interstellar medium. The abundances calculated as the conditions evolve can then be utilized as reasonable initial conditions for a theory of the chemistry of dense cores. Methods. Hydrodynamic shock-wave simulations of the early stages of cold core formation are used to determine the time-dependent physical conditions for a gas-grain chemical network. We follow the cold post-shock molecular evolution of ices and gas-phase molecules as the visual extinction increases with time to A V ≈ 3. (Note that instead of an equal sign, the approximately equal sign should remain.) At higher extinction, self-gravity becomes important. Results. As the newly condensed gas enters its cool post-shock phase, a large amount of CO is produced in the gas. As the CO forms, water ice is produced on grains, while accretion of CO produces CO ice. The production of CO 2 ice from CO occurs via several surface mechanisms, while the production of CH 4 ice is slowed by gas-phase conversion of C into CO.

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“…Gibb et al (2004). Figure 5 shows that the CO 2 and CH 3 OH ice abundances toward protostars and background stars from Boogert et al (2011) are similar, and that the Taurus CO 2 ice abundances from Whittet et al (2007) are poor templates for ice abundances toward average cloud cores. Boogert et al (2011) show that there is also no statistically significant difference in the C1-4 components between the protostars and background stars, but the C5 component is absent in cloud sources.The only other feature that is present exclusively toward protostars is pure CO 2 ice, which is proposed to form from thermally induced ice segregation or distillation.…”

Section: Cloud Versus Protostellar Icesmentioning

confidence: 97%

Ices in Starless and Starforming Cores

et al. 2011

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Abstract. Icy grain mantles are commonly observed through infrared spectroscopy toward dense clouds, cloud cores, protostellar envelopes and protoplanetary disks. Up to 80% of the available oxygen, carbon and nitrogen are found in such ices; the most common ice constituents -H 2 O, CO2 and CO -are second in abundance only to H2 in many star forming regions. In addition to being a molecular reservoir, ice chemistry is responsible for much of the chemical evolution from H2 O to complex, prebiotic molecules. Combining the exisiting ISO, Spitzer, VLT and Keck ice data results in a large sample of ice sources (∼80) that span all stages of star formation and a large range of protostellar luminosities (<0.1-10 5 L ). Here we summarize the different techniques that have been applied to mine this ice data set on information on typical ice compositions in different environments and what this implies about how ices form and evolve during star and planet formation. The focus is on how to maximize the use of empirical constraints from ice observations, followed by the application of information from experiments and models. This strategy is used to identify ice bands and to constrain which ices form early during cloud formation, which form later in the prestellar core and which require protostellar heat and/or UV radiation to form. The utility of statistical tests, survival analysis and ice maps is highlighted; the latter directly reveals that the prestellar ice formation takes place in two phases, associated with H 2 O and CO ice formation, respectively, and that most protostellar ice variation can be explained by differences in the prestellar CO ice formation stage. Finally, special attention is paid to the difficulty of observing complex ices directly and how gas observations, experiments and models help in constraining this ice chemistry stage.

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The Abundance of Carbon Dioxide Ice in the Quiescent Intracloud Medium

Cited by 122 publications

References 57 publications

The influence of temperature on the synthesis of molecules on icy grain mantles in dense molecular clouds

The influence of temperature on the synthesis of molecules on icy grain mantles in dense molecular clouds

Beyond the pseudo-time-dependent approach: chemical models of dense core precursors

Ices in Starless and Starforming Cores

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