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Anti-parallel EUV flows observed along active region filament threads with Hi-C  

Caroline Alexander   Submitted: 2013-06-24 07:25

Plasma flows within prominences/filaments have been observed for many years and hold valuable clues concerning the mass and energy balance within these structures. Previous observations of these flows primarily come from Hα and cool EUV lines (e.g., 304A) where estimates of the size of the prominence threads has been limited by the resolution of the available instrumentation. Evidence of `counter-steaming' flows has previously been inferred from these cool plasma observations but now, for the first time, these flows have been directly imaged along fundamental filament threads within the million degree corona (at 193A). In this work we present observations of an active region filament observed with Hi-C that exhibits anti-parallel flows along adjacent filament threads. Complementary data from SDO/AIA and HMI are presented. The ultra-high spatial and temporal resolution of Hi-C allow the anti-parallel flow velocities to be measured (70-80 km s-1) and gives an indication of the resolvable thickness of the individual strands (0.8'' ± 0.1''). The temperature distribution of the plasma flows was estimated to be log T(K) = 5.45 ± 0.10 using EM loci analysis. We find that SDO/AIA cannot clearly observe these anti-parallel flows nor measure their velocity or thread width due to its larger pixel size. We suggest that anti-parallel/counter-streaming flows are likely commonplace within all filaments and are currently not observed in EUV due to current instrument spatial resolution.

Authors: Caroline E. Alexander, Robert W. Walsh, Stephane Regnier, Jonathan Cirtain, Amy R. Winebarger, Leon Golub, Ken Kobayashi, Simon Platt, Nick Mitchell, Kelly Korreck, Bart DePontieu, Craig DeForest, Mark Weber, Alan Title, Sergey Kuzin
Projects: Other,SDO-AIA

Publication Status: Published in ApJ, 775, L32
Last Modified: 2013-09-13 09:55
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Hinode observations and 3D magnetic structure of an X-ray bright point  

Caroline Alexander   Submitted: 2011-02-01 06:47

Aims: We present complete Hinode Solar Optical Telescope (SOT), X-Ray Telescope (XRT)and EUV Imaging Spectrometer (EIS) observations of an X-ray bright point (XBP) observed on the 10, 11 of October 2007 over its entire lifetime (~12 h). We aim to show how the measured plasma parameters of the XBP change over time and also what kind of similarities the X-ray emission has to a potential magnetic field model. Methods: Information from all three instruments on-board Hinode was used to study its entire evolution. XRT data was used to investigate the structure of the bright point and to measure the X-ray emission. The EIS instrument was used to measure various plasma parameters over the entire lifetime of the XBP. Lastly, the SOT was used to measure the magnetic field strength and provide a basis for potential field extrapolations of the photospheric fields to be made. These were performed and then compared to the observed coronal features. Results: The XBP measured ~15″ in size and was found to be formed directly above an area of merging and cancelling magnetic flux on the photosphere. A good correlation between the rate of X-ray emission and decrease in total magnetic flux was found. The magnetic fragments of the XBP were found to vary on very short timescales (minutes), however the global quasi-bipolar structure remained throughout the lifetime of the XBP. The potential field extrapolations were a good visual fit to the observed coronal loops in most cases, meaning that the magnetic field was not too far from a potential state. Electron density measurements were obtained using a line ratio of Fe XII and the average density was found to be 4.95 x 109 cm-3 with the volumetric plasma filling factor calculated to have an average value of 0.04. Emission measure loci plots were then used to infer a steady temperature of log Te [ K] ~ 6.1. The calculated Fe XII Doppler shifts show velocity changes in and around the bright point of ±15 km s-1 which are observed to change on a timescale of less than 30 min.

Authors: Alexander, C. E.; Del Zanna, G.; Maclean, R. C.
Projects: Hinode/EIS,Hinode/SOT,Hinode/XRT

Publication Status: A&A (published)
Last Modified: 2011-02-02 07:02
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Anti-parallel EUV flows observed along active region filament threads with Hi-C
Hinode observations and 3D magnetic structure of an X-ray bright point

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