Calculated spectra for HeH⁺ and its effect on the opacity of cool metal-poor stars     

Elodie A. Engel  Natasha Doss  Gregory J. Harris  Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2005,357(2):471-477

The wavelength and Einstein A coefficient are calculated for all rotation–vibration transitions of  ⁴He¹H⁺, ³He¹H⁺, ⁴He²H⁺  and  ³ He²H⁺  , giving a complete line list and the partition function for  ⁴HeH⁺  and its isotopologues. This opacity is included in the calculation of the total opacity of low-metallicity stars and its effect is analysed for different conditions of temperature, density and hydrogen number fraction. For a low helium number fraction (as in the Sun), it is found that HeH⁺ has a visible but small effect for very low densities  (ρ≤ 10⁻¹⁰ g cm⁻³)  , at temperatures around 3500 K. However, for high helium number fraction, the effect of HeH⁺ becomes important for higher densities  (ρ≤ 10⁻⁶ g cm⁻³)  , its effect being most important for a temperature around 3500 K. Synthetic spectra for a variety of different conditions are presented.  相似文献   

A laboratory survey of the thermal desorption of astrophysically relevant molecules     

Mark P. Collings  Mark A. Anderson  Rui Chen  John W. Dever  Serena Viti  David A. Williams  Martin R. S. McCoustra 《Monthly notices of the Royal Astronomical Society》2004,354(4):1133-1140

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Electron-impact rotational excitation of water     

Alexandre Faure  Jimena D. Gorfinkiel  Jonathan Tennyson 《Monthly notices of the Royal Astronomical Society》2004,347(1):323-333

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Evolution of bimodal accretion flows     

J. Gracia  J. Peitz  Ch. Keller  M. Camenzind 《Monthly notices of the Royal Astronomical Society》2003,344(2):468-472

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The effect of grain size distribution on H₂ formation rate in the interstellar medium     

Azi Lipshtat  Ofer Biham 《Monthly notices of the Royal Astronomical Society》2005,362(2):666-670

The formation of molecular hydrogen  (H₂)  in the interstellar medium takes place on the surfaces of dust grains. Hydrogen molecules play a role in gas-phase reactions that produce other molecules, some of which serve as coolants during gravitational collapse and star formation. Thus, the evaluation of the production rate of hydrogen molecules and its dependence on the physical conditions in the cloud are of great importance. Interstellar dust grains exhibit a broad size distribution in which the small grains capture most of the surface area. Recent studies have shown that the production efficiency strongly depends on the grain composition and temperature as well as on its size. In this paper, we present a formula that provides the total production rate of  H₂  per unit volume in the cloud, taking into account the grain composition and temperature as well as the grain size distribution. The formula agrees very well with the master equation results. It shows that for a physically relevant range of grain temperatures, the production rate of  H₂  is significantly enhanced due to their broad size distribution.  相似文献   

Combined element (H and C) stable isotope ratios of methane in carbonaceous chondrites     

Anna L. Butterworth  Olivier Aballain  Jerome Chappellaz  Mark A. Sephton † 《Monthly notices of the Royal Astronomical Society》2004,347(3):807-812

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NCCN in TMC-1 and IRC+10216     

S. Petrie  T. J. Millar  A. J. Markwick 《Monthly notices of the Royal Astronomical Society》2003,341(2):609-616

We employ quantum chemical calculations using the CBS-RAD ('Complete Basis Set – Radicals') technique on the C₂N₂H potential energy surface to show that the reaction of HNC with CN is a viable and plausible route to NCCN in cold astrophysical environments. We use detailed chemical kinetic models to predict the abundance of NCCN in TMC-1 and IRC+10216. Radio-astronomical detection of NCCN is precluded by its lack of a dipole moment. We discuss other prospects for its observation in interstellar and circumstellar environments, by space-borne infrared spectroscopy, indirectly by detection of the NCCNH⁺ ion, or inferentially by detection of its higher-energy, polar isomer CNCN.  相似文献   

The instability of fast shocks in molecular clouds     

Michael D. Smith  Alexander Rosen 《Monthly notices of the Royal Astronomical Society》2003,339(1):133-147

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分子云浓核的密度和磁场     

郑兴武  黄永锋 《中国天文和天体物理学报》1996,(3)

利用均匀磁化球模型，对OrionB云中的39个分子云浓核，从它们观测的源半径和分子线线宽，推求它们的数密度和磁场．得到平均磁场110μG，平均密度为8×104／cm3．这些计算值与观测结果一致．对于R＞0．2pc的分子云浓核，利用均匀磁化球模型推求磁场和数密度的方法是一种可行的方法．  相似文献   

Molecular hydrogen formation on porous dust grains     

Hagai B. Perets  Ofer Biham 《Monthly notices of the Royal Astronomical Society》2006,365(3):801-806

Recent laboratory experiments on interstellar dust analogues have shown that H₂ formation on dust-grain surfaces is efficient in a range of grain temperatures below 20 K. These results indicate that surface processes may account for the observed H₂ abundance in cold diffuse and dense clouds. However, high abundances of H₂ have also been observed in warmer clouds, including photon-dominated regions (PDRs), where grain temperatures may reach 50 K, making the surface processes extremely inefficient. It was suggested that this apparent discrepancy can be resolved by chemisorption sites. However, recent experiments indicate that chemisorption processes may not be efficient at PDR temperatures. Here we consider the effect of grain porosity on H₂ formation, and analyse it using a rate-equation model. It is found that porosity extends the efficiency of the recombination process to higher temperatures. This is because H atoms that desorb from the internal surfaces of the pores may re-adsorb many times and thus stay longer on the surface. However, this porosity-driven extension may enable efficient H₂ formation in PDRs only if porosity also contributes to significant cooling of the grains, compared to non-porous grains.  相似文献