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The theory of formation of various molecules, both on surfaces of interstellar dust-grains and in gas-phase reactions, is reviewed. Destruction of molecules, the special problems of very dark clouds and the life-history of dust-grains are also reviewed briefly.
The ionization equilibrium of carbon and heavier elements in a neutral gas cloud close to an early type star is discussed using a simple model for the transfer of the ultra-violet radiation. The balance between atomic and molecular hydrogen is also considered. It is concluded that the H II region exciting star may be, but should not be assumed to be, the source of the photons which ionize carbon in...
Our present knowledge of stars associated with dark clouds is reviewed with emphasis placed on the observational properties and large-scale behavior of young stars.
This report deals with radio observations of the carbon and narrow hydrogen recombination lines. The theoretical discussion of these data are contained in the paper by Walmsley, in this volume.
A summary of recent interstellar molecular line work will be presented. Transitions of the follwing molecules have been detected in Sgr B2: Vinylcyanide, H2C2HCN, formic acid, HCOOH, dimethyl ether (CH3)2O and isotopically labelled cyanoacetylene — 13C,HC13CCN and HCC13CN. The data on cyanoacetylene give an upper limit to the abundance ratio 12C/13C of 36 ± 5. A short discussion of the interstellar...
A model for W3(A) is described and the results of the calculations for the dynamical evolution of a compact HII region with a dust front are discussed.
We compare parameters derived from the observed radio and near-infrared flux densities of a sample of 21 compact H II regions with theoretical parameters calculated for dusty Strömgren spheres. Preliminary results of this comparison suggest that the dust inside compact H II regions is quite often depleted by large factors, consistent with evaporation of the mantle material of core-mantle particles.
Most infrared sources found at λ < 40μ and associated with HII regions appear to fall into one of three classes which may be loosely referred to as the reddened 0 stars, the compact HII regions and the protostellar objects. However recent observations indicate that the distinction between the last two types is blurred.
A brief account of the techniques used at λ > 40 μm is followed by photometric data, maps of IR regions and spectral data. In particular the He+/H+ ratio is discussed and new features on maps of W3 and the Galactic Centre are presented.
Small dense clumps of ionized gas exist during various stages in the evolution of H II regions. They can be manifest as bright rims or as very small, very compact H II regions surrounding new born stars. Examples of both types of objects are given and some speculation is made about how massive stars are formed.
A summary is given of evidence supporting the hypothesis that the helium abundance is constant throughout the Galaxy and that variations in observed ionized helium abundance are due to selective absorption of the helium ionizing photons by dust in the H II regions. New support comes from mapping of the recombination lines in the Orion Nebula and from detection of He+ in the region of the galactic...
From new observational data, Georgelin, Lortet-Zuckermann and Monnet (1975) and Chopinet and Lortet-Zuckermann (1975) have rediscussed the use of the Zanstra method in order to derive the rate of stellar ultra-violet photons from hot stars and have studied the relation between the excitation of the nebular spectrum and the spectral type of the exciting star. I wish to show here that dust grains mixed...
A large number of maser sources of OH and H2O are now known to be associated with H II regions. In general, they are the most powerful maser sources discovered in our Galaxy. This report deals with three problems: (a) a pumping mechanism for OH and H2O masers; (2) formation of maser condensations; (3) mechanisms for the polarization of maser emission. We then summarize the complete picture for OH...
Recently several emissionlines from rotational transitions in vibrationally excited levels of SiO have been detected. The first source was found in the Kleinmann-Low (KL) nebula in Orion. Most likely the radiation source is an astrophysical maser, perhaps associated with the Becklin Neugebauer (BN) object. Following the detection of the SiO maser in Orion, the same radiation has been found from a...
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