Densities circumstellar shells

We can estimate the column density of material in a circumstellar shell, NH, extending from radius R to infinite distance, from the expression ... 

However, as temperatures and densities drop steeply in the circumstellar shell with increasing distance from the central star, reaction kinetics may no longer permit establishment of thermochemical equilibrium in the stellar outflow 4). Detailed and generally applicable discussions of the reaction kinetics relevant here can be found in 52, 53). Let us follow a parcel of hot atmospheric gas traveling away from the photosphere and assume that a certain gas is produced or destroyed by some reaction in the CSE. As long as chemical... 

At temperatures and densities of circumstellar shells, the chemistry is in general likely to be highly non-equilibrium. However, in the hotter and denser Inner parts of stellar winds, oiroumstellar shells and in particular cool stellar atmospheres, equilibrium chemistry may be a reasonable approximation, and can at least give us a basis from which non-equillbrium chemistry could be considered. 

The surface distribution of M stars is studied by differentiating them according to whether they show a circumstellar dust shell (CS) or not. Analysis shows that galactic latitudinal and longitudinal distributions are not determined by spectral subclasses alone. The study also indicates that the M type stars with CS have higher intrinsic luminosities in the K band than those without CS. The M stars used in the study are obtained from the Two Micron Sky Survey catalogue (IRC) which is an unbiased sample with respect to the interstellar extinction. The CS feature is identified by the ratio of flux densities at 12 and 25 m in the IRAS point source catalog. 

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