Non--local radiative transfer in strongly inverted masers

Abstract

Maser transitions are commonly observed in media exhibiting a large range of densities and temperatures. They can be used to obtain information on the dynamics and physical conditions of the observed regions. In order to obtain reliable constraints on the physical conditions prevailing in the masing regions, it is necessary to model the excitation mechanisms of the energy levels of the observed molecules. We present a numerical method that enables us to obtain self-consistent solutions for both the statistical equilibrium and radiative transfer equations. Using the standard maser theory, the method of Short Characteristics is extended to obtain the solution of the integro-differential radiative transfer equation, appropriate to the case of intense masing lines. We have applied our method to the maser lines of the H2O molecule and we compare with the results obtained with a less accurate approach. In the regime of large maser opacities we find large differences in the intensity of the maser lines that could be as high as several orders of magnitude. The comparison between the two methods shows, however, that the effect on the thermal lines is modest. Finally, the effect introduced by rate coefficients on the prediction of H2O masing lines and opacities is discussed, making use of various sets of rate coefficients involving He, o-H2 and p-H2. We find that the masing nature of a line is not affected by the selected collisional rates. However, from one set to the other the modelled line opacities and intensities can vary by up to a factor ~2 and ~10 respectively.

References in corpus (9)

• Quasi-classical rate coefficient calculations for the rotational (de)excitation of H2O by H2
• Water Vapor around Sgr B2
• Physical conditions in shocked regions of Orion from ground-based observations of H_2O
• A multi-transition submillimeter water maser study of evolved stars - detection of a new line near 475 GHz
• Solving radiative transfer with line overlaps using Gauss Seidel algorithms
• Gaussian Spectral Line Profiles of Astrophysical Masers
• Submillimeter and Millimeter Masers
• Non--local radiative transfer in strongly inverted masers
• Masers and star formation

Cited by in corpus (13)

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• VERA and ALMA Observations of the H2O Supermaser Burst in Orion KL
• ATOMIUM: Probing the inner wind of evolved O-rich stars with new, highly excited H${}_2$O and OH lines
• Collisional excitation of water by hydrogen atoms
• MOLPOP-CEP: An Exact, Fast Code for Multi-Level Systems
• First detection of the 448 GHz H2O transition in space
• Non--local radiative transfer in strongly inverted masers
• Vibrationally excited water emission at 658 GHz from evolved stars
• A New 3D Maser Code Applied to Flaring Events
• First detection of THz water maser in NGC7538-IRS1 with SOFIA and new 22 GHz e-MERLIN maps
• Collisional Pumping of H${}_2$O and CH${}_3$OH Masers in C-Type Shock Waves