Structure of prominence legs: plasma and magnetic field

Levens, P.J., Schmieder, B., Labrosse, N. and Ariste, A. L. (2016) Structure of prominence legs: plasma and magnetic field. Astrophysical Journal, 818(1), 31. (doi:10.3847/0004-637X/818/1/31)

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Abstract

We investigate the properties of a "solar tornado" observed on 2014 July 15, and aim to link the behavior of the plasma to the internal magnetic field structure of the associated prominence. We made multi-wavelength observations with high spatial resolution and high cadence using SDO/AIA, the Interface Region Imaging Spectrograph (IRIS) spectrograph, and the Hinode/Solar Optical Telescope (SOT) instrument. Along with spectropolarimetry provided by the Télescope Héliographique pour l'Etude du Magnétisme et des Instabilités Solaires telescope we have coverage of both optically thick emission lines and magnetic field information. AIA reveals that the two legs of the prominence are strongly absorbing structures which look like they are rotating, or oscillating in the plane of the sky. The two prominence legs, which are both very bright in Ca ii (SOT), are not visible in the IRIS Mg ii slit-jaw images. This is explained by the large optical thickness of the structures in Mg ii, which leads to reversed profiles, and hence to lower integrated intensities at these locations than in the surroundings. Using lines formed at temperatures lower than 1 MK, we measure relatively low Doppler shifts on the order of ±10 km s−1 in the tornado-like structure. Between the two legs we see loops in Mg ii, with material flowing from one leg to the other, as well as counterstreaming. It is difficult to interpret our data as showing two rotating, vertical structures that are unrelated to the loops. This kind of "tornado" scenario does not fit with our observations. The magnetic field in the two legs of the prominence is found to be preferentially horizontal.

Item Type:Articles
Status:Published
Refereed:Yes
Glasgow Author(s) Enlighten ID:Labrosse, Dr Nicolas and Levens, Peter
Authors: Levens, P.J., Schmieder, B., Labrosse, N., and Ariste, A. L.
College/School:College of Science and Engineering > School of Physics and Astronomy
Journal Name:Astrophysical Journal
Publisher:IOP Publishing
ISSN:0004-637X
ISSN (Online):1538-4357
Copyright Holders:Copyright © 2016 The American Astronomical Society
First Published:First published in Astrophysical Journal 818(1): 31
Publisher Policy:Reproduced in accordance with the publisher copyright policy
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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
619541STFC Doctoral Training Grant 2012-17Martin HendryScience & Technologies Facilities Council (STFC)ST/K502005/1S&E P&A - PHYSICS & ASTRONOMY
631581Consolidated grant in solar and astrophysical plasmasLyndsay FletcherScience & Technologies Facilities Council (STFC)ST/L000741/1S&E P&A - PHYSICS & ASTRONOMY