Astrophysical water masers: Line profiles analysis

Abstract

The changes in the spectral line profile of the 22GHz H2O maser are calculated as a function of emerging maser flux. We address not only the narrowing and re-broadening of the maser lines, but also the deviations of Gaussian symmetry as a result of the various hyperfine components of the 22 GHz maser line. Non-LTE models of the H2O maser transition, including hyperfine structure and cross-relaxation, are compared with high spectral resolution Very Long Baseline Interferometry (VLBI) observations of the H2O masers in the circumstellar envelopes (CSEs) of a sample of late-type stars. This yields estimates on the thermal width in the maser region as well as the emerging maser flux and thus the level of saturation. We also discuss the effect of a velocity gradient along the maser path on the line widths and shapes of the line profile and the effect of the geometry of the maser region. We find that the typical velocity shift along the maser path is of the order of 1.0 km/s. The effect of this shift on the shape of the maser spectrum is difficult to distinguish from the effect of the hyperfine components.

arXiv comment8 pages; 6 figures. Accepted for publication in A&A

References in corpus (3)

• Circular Polarization of Water Masers in the Circumstellar Envelopes of Late Type Stars
• Circular Polarization of Circumstellar Water Masers around S Per
• Gaussian Spectral Line Profiles of Astrophysical Masers

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• Magnetic field regulated infall on the disc around the massive protostar Cepheus A HW2
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• The magnetic field of the proto-planetary nebula candidate IRAS 19296+2227
• Polarization of Water Masers in the presence of Velocity and Magnetic Field Gradients
• First detection of circular polarization in 4.7 GHz excited OH masers