Hα line profile asymmetries and the chromospheric flare velocity field

Kuridze, D. et al. (2015) Hα line profile asymmetries and the chromospheric flare velocity field. Astrophysical Journal, 813(2), 125. (doi: 10.1088/0004-637X/813/2/125)

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The asymmetries observed in the line profiles of solar flares can provide important diagnostics of the properties and dynamics of the flaring atmosphere. In this paper the evolution of the Halpha and Ca II 8542 {\AA} lines are studied using high spatial, temporal and spectral resolution ground-based observations of an M1.1 flare obtained with the Swedish 1-m Solar Telescope. The temporal evolution of the Halpha line profiles from the flare kernel shows excess emission in the red wing (red asymmetry) before flare maximum, and excess in the blue wing (blue asymmetry) after maximum. However, the Ca II 8542 {\AA} line does not follow the same pattern, showing only a weak red asymmetry during the flare. RADYN simulations are used to synthesise spectral line profiles for the flaring atmosphere, and good agreement is found with the observations. We show that the red asymmetry observed in Halpha is not necessarily associated with plasma downflows, and the blue asymmetry may not be related to plasma upflows. Indeed, we conclude that the steep velocity gradients in the flaring chromosphere modifies the wavelength of the central reversal in the Halpha line profile. The shift in the wavelength of maximum opacity to shorter and longer wavelengths generates the red and blue asymmetries, respectively.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Graham, Mr David and Simoes, Dr Paulo and Fletcher, Professor Lyndsay
Authors: Kuridze, D., Mathioudakis, M., Simoes, P., Rouppe van der Voort, L., Carlsson, M., Jafarzadeh, S., Allred, J., Kowalski, A., Kennedy, M., Fletcher, L., Graham, D., and Keenan, F. P.
Subjects:Q Science > QB Astronomy
College/School:College of Science and Engineering > School of Physics and Astronomy
Research Group:Astronomy & Astrophysics
Journal Name:Astrophysical Journal
Journal Abbr.:ApJ
Publisher:American Astronomical Society
ISSN (Online):1538-4357
Copyright Holders:Copyright © 2015 American Astronomical Society
First Published:First published in Astrophysical Journal 813(2):125
Publisher Policy:Reproduced in accordance with the copyright policy of the publisher
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
595181Chromospheric Flares: Observations, Models and Archives (CHROMA)Lyndsay FletcherEuropean Commission (EC)606862P&A - PHYSICS & ASTRONOMY