Organic molecules in protoplanetary disks around T Tauri and Herbig Ae stars

Thi, Wing-Fai; Zadelhoff, Gerd-Jan van; Dishoeck, E. F. van

doi:10.1051/0004-6361:200400026

Cited by 206 publications

(296 citation statements)

References 78 publications

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“…In the cold mid-plane (< 20 K), most molecules are frozen out onto the grains. This layered chemical structure is consistent with observations of ions and radicals with abundance ratios that are similar or higher than those found in PDRs (e.g., [14,70]). If the UV radiation is energetic enough to dissociate CO, isotope selective processes may occur leading to fractionation of CO isotopes which can eventually be incorporated into meteorites [46].…”

Section: Introductionsupporting

confidence: 89%

Photoprocesses in protoplanetary disks

2006

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Circumstellar disks are exposed to intense ultraviolet (UV) radiation from the young star. In the inner disks, the UV radiation can be enhanced by more than seven orders of magnitude compared with the average interstellar radiation field, resulting in a physical and chemical structure that resembles that of a dense photon-dominated region (PDR). This intense UV field affects the chemistry, the vertical structure of the disk, and the gas temperature, especially in the surface layers. The parameters which make disks different from more traditional PDRs are discussed, including the shape of the UV radiation field, grain growth, the absence of PAHs, the gas/dust ratio and the presence of inner holes. Illustrative infrared spectra from the Spitzer Space Telescope are shown. New photodissociation cross sections for selected species, including simple ions, are presented. Also, a summary of cross sections at the Lyman α 1216Å line, known to be strong for some T Tauri stars, is made. Photodissociation and ionization rates are computed for different radiation fields with color temperatures ranging from 30000 to 4000 K and grain sizes up to a few µm. The importance of a proper treatment of the photoprocesses is illustrated for the transitional disk toward HD 141569A which includes grain growth.

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Section: Introductionsupporting

confidence: 89%

Photoprocesses in protoplanetary disks

2006

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“…To correct the observed emission line brightness temperatures for beam dilution, we assume that (Thi et al 2004)…”

Section: Appendix A: Individual Galaxies Appendix B: Beam/source Coupmentioning

confidence: 99%

TANGO I: Interstellar medium in nearby radio galaxies

Flaquer¹,

Léon²,

Combes³

et al. 2010

A&A

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Context. Powerful radio-AGN are hosted by massive elliptical galaxies that are usually very poor in molecular gas. Nevertheless, gas is needed at their very center to feed the nuclear activity. Aims. We study the molecular gas properties (i.e., mass, kinematics, distribution, origin) of these objects, and compare them with results for other known samples. Methods. At the IRAM-30m telescope, we performed a survey of the CO(1-0) and CO(2-1) emission from the most powerful radio galaxies of the Local Universe, selected only on the basis of their radio continuum fluxes. Results. The main result of our survey is that the molecular gas content of these galaxies is very low compared to spiral or FIR-selected galaxies. The median value of the molecular gas mass, including detections and upper limits, is 2.2 × 10 8 M . When separated into FR-I and FR-II types, a difference in their H 2 masses is found. The median value of FR-I galaxies is about 1.9 × 10 8 M and higher for FR-II galaxies, at about 4.5 × 10 8 M . Which is probably entirely because of a Malmquist bias. Our results contrast with those of previous surveys, whose targets were mainly selected by means of their FIR emission, implying that we measure higher observed masses of molecular gas. Moreover, the shape of CO spectra suggest that a central molecular gas disk exists in 30% of these radio galaxies, a lower rate than in other active galaxy samples. Conclusions. We find a low level of molecular gas in our sample of radio-selected AGNs, indicating that galaxies do not need much molecular gas to host an AGN. The presence of a molecular gas disk in some galaxies and the wide range of molecular gas masses may be indicative of different origins for the gas, which we can not exclude at present (e.g., minor/major mergers, stellar mass loss, or accretion).

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“…[1][2][3][4][5][6] In addition, both ethanol and OH have been detected in interstellar molecular clouds and star forming regions (hot and cold cores) such as W3(OH) and Sgr B2, where temperatures can reach as low as 40 K. [7][8][9][10][11][12][13] Millar et al 12 suggested that ethanol could potentially be used as a chemical clock for hot cores if the kinetics of its reactions with species including the hydroxyl radical were better understood at temperatures pertinent to such environments. Conducting kinetic studies with species known to be present in these cold environments is important for the advancement of chemical models of these regions.…”

Section: Introductionmentioning

confidence: 99%

Measurements of Rate Coefficients for Reactions of OH with Ethanol and Propan-2-ol at Very Low Temperatures

et al. 2014

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The low temperature kinetics of the reactions of OH with ethanol and propan-2-ol have been studied using a pulsed Laval nozzle apparatus coupled with pulsed laser photolysis -laser induced fluorescence (PLP-LIF) spectroscopy. The rate coefficients for both reactions have been found to increase significantly as the temperature is lowered, by~a factor of 18 between 293 and 54 K for ethanol, and by~10 between 298 and 88 K for OH + propan-2-ol. The pressure dependence of the rate coefficients provide evidence for two reaction channels; a zero pressure bimolecular abstraction channel leading to products and collisional stabilization of a weakly bound OH-alcohol complex. The presence of the abstraction channel at low temperatures is rationalized by a quantum mechanical tunneling mechanism, most likely through the barrier to hydrogen abstraction from the OH moiety on the alcohol.

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Organic molecules in protoplanetary disks around T Tauri and Herbig Ae stars

Cited by 206 publications

References 78 publications

Photoprocesses in protoplanetary disks

Photoprocesses in protoplanetary disks

TANGO I: Interstellar medium in nearby radio galaxies

Measurements of Rate Coefficients for Reactions of OH with Ethanol and Propan-2-ol at Very Low Temperatures

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