Fan Loops Observed by IRIS, EIS, and AIA

Journal Article · Wed Feb 01 04:00:00 EST 2017 · Astrophysical Journal

DOI:https://doi.org/10.3847/1538-4357/835/2/244· OSTI ID:22869468

Ghosh, Avyarthana; Tripathi, Durgesh; Gupta, G. R. ^[1]; Polito, Vanessa; Mason, Helen E. ^[2]

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1. Inter-University Centre for Astronomy and Astrophysics, Post Bag—4, Ganeshkhind, Pune 411007 (India)
2. Department of Applied Mathematics and Theoretical Physics, Wilberforce Road, Cambridge CB3 0WA (United Kingdom)

A comprehensive study of the physical parameters of active region fan loops is presented using the observations recorded with the Interface Region Imaging Spectrometer (IRIS), the EUV Imaging Spectrometer (EIS) on board Hinode, and the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The fan loops emerging from non-flaring AR 11899 (near the disk center) on 2013 November 19 are clearly discernible in AIA 171 Å images and in those obtained in Fe viii and Si vii images using EIS. Our measurements of electron densities reveal that the footpoints of these loops are at an approximately constant pressure with electron densities of log N{sub e}=10.1 cm{sup −3} at log [T/K]=5.15 (O iv), and log N{sub e}=8.9 cm{sup −3} at log [T/K]=6.15 (Si x). The electron temperature diagnosed across the fan loops by means of EM-Loci suggest that two temperature components exist at log [T/K]=4.95 and 5.95 at the footpoints. These components are picked up by IRIS lines and EIS lines, respectively. At higher heights, the loops are nearly isothermal at log [T/K]=5.95, which remained constant along the loop. The measurement of the Doppler shift using IRIS lines suggests that the plasma at the footpoints of these loops is predominantly redshifted by 2–3 km s{sup −1} in C ii, 10–15 km s{sup −1} in Si iv, and 15–20 km s{sup −1} in O iv, reflecting the increase in the speed of downflows with increasing temperature from log [T/K]=4.40 to 5.15. These observations can be explained by low-frequency nanoflares or impulsive heating, and provide further important constraints on the modeling of the dynamics of fan loops.

• OSTI ID: 22869468
• Journal Information: Astrophysical Journal, Journal Name: Astrophysical Journal Journal Issue: 2 Vol. 835; ISSN ASJOAB; ISSN 0004-637X
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
CHROMOSPHERE
COMPUTERIZED SIMULATION
DOPPLER EFFECT
ELECTRON DENSITY
ELECTRON TEMPERATURE
HEIGHT
INTERFACES
MAGNETIC FIELDS
PLASMA
RED SHIFT
SPECTROMETERS
SUN
ULTRAVIOLET RADIATION
VELOCITY