On the apparent narrowing of radio recombination lines at high principal quantum numbers

Date
2011
Authors
Alexander, J
and Gulyaev, S
Supervisor
Item type
Journal Article
Degree name
Journal Title
Journal ISSN
Volume Title
Publisher
IOPScience
Abstract

We critically analyze the Bell et al. findings on "anomalous" widths of high-order Hydrogen radio recombination lines in the Orion Nebula at 6 GHz. We review their method of modified frequency switching and show that the way this method is used for large \Delta n is not optimal and can lead to misinterpretation of measured spectral line parameters. Using a model of the Orion Nebula, conventional broadening theory and Monte Carlo simulation, we determine a transition-zone n = 224...241 (\Delta n = 11...14), where measurement errors grow quickly with n and become comparable with the measurement values themselves. When system noise and spectrum channelization are accounted for, our simulation predicts "processed" line narrowing in the transition-zone similar to that reported by Bell et al. We find good agreement between our simulation results and their findings, both in line temperatures and widths. We conclude, therefore, that Bell et al.'s findings do not indicate a need to revise Stark broadening theory.

Description
Keywords
Astrometry , Kuiper belt , General , Planets and satellites , Dynamical evolution and stability , Formation
Source
The Astrophysical Journal, 745:194 (6pp), 2012 February 1
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