Water masers in a protostellar gas cloud

TLDR: In this paper, the transfer of line radiation in a gas containing model water molecules with thirty-one pure rotational levels was calculated and two simple approximations of H2-H20 collisional cross sections were used.

Abstract: Population inversion of the 6/sub 16/-5/sub 23/ transition of water molecules is a natural consequence of the breakdown of thermal equilibrium in the outer layers of a dense gas cloud Approaching the surface of the cloud from below, radiation of different lines starts to escape at different depths Energy is continuously pumped into the lines since the molecules are coupled to the reservoir of kinetic energy of the gas by collisions with hydrogen molecules In support of this picture the transfer of line radiation in a gas containing model water molecules with thirty-one pure rotational levels was calculated Two simple approximations of H2-H20 collisional cross sections were used: (A) The cross sections were assumed to be proportional to the square of the matrix elements of the dipole transitions; (B) All cross sections were assumed to be equal to the geometrical cross section, still following dipole selection rules Population inversion of the 6/sub 16/-5/sub 23/ transition occurred for both collisional models since the breakdown of thermial equilibrium is governed by the line opacities The required amplification could only be produced in case (A) The level populations of some other- transitions of water become also inverted One particular class of molecular masermore » sources could be produced by limb brightening'' in the cocoon'' around new born O stars This may explain the observed coincidence with bright knots'' in the continuum radiation of H II regions (auth)« less