skip to main content
OSTI.GOV title logo U.S. Department of Energy
Office of Scientific and Technical Information

Title: EUV SPECTRAL LINE FORMATION AND THE TEMPERATURE STRUCTURE OF ACTIVE REGION FAN LOOPS: OBSERVATIONS WITH HINODE/EIS AND SDO/AIA

Abstract

With the aim of studying active region fan loops using observations from the Hinode EUV Imaging Spectrometer (EIS) and Solar Dynamics Observatory Atmospheric Imaging Assembly (AIA), we investigate a number of inconsistencies in modeling the absolute intensities of Fe VIII and Si VII lines, and address why spectroheliograms formed from these lines look very similar despite the fact that ionization equilibrium calculations suggest that they have significantly different formation temperatures: log(T{sub e} /K) = 5.6 and 5.8, respectively. It is important to resolve these issues because confidence has been undermined in their use for differential emission measure (DEM) analysis, and Fe VIII is the main contributor to the AIA 131 A channel at low temperatures. Furthermore, the strong Fe VIII 185.213 A and Si VII 275.368 A lines are the best EIS lines to use for velocity studies in the transition region, and for assigning the correct temperature to velocity measurements in the fans. We find that the Fe VIII 185.213 A line is particularly sensitive to the slope of the DEM, leading to disproportionate changes in its effective formation temperature. If the DEM has a steep gradient in the log(T{sub e} /K) = 5.6-5.8 temperature range, or is stronglymore » peaked, Fe VIII 185.213 A and Si VII 275.368 A will be formed at the same temperature. We show that this effect explains the similarity of these images in the fans. Furthermore, we show that the most recent ionization balance compilations resolve the discrepancies in absolute intensities. With these difficulties overcome, we combine EIS and AIA data to determine the temperature structure of a number of fan loops and find that they have peak temperatures of 0.8-1.2 MK. The EIS data indicate that the temperature distribution has a finite (but narrow) width < log ({sigma}{sub Te}/K) = 5.5 which, in one detailed case, is found to broaden substantially toward the loop base. AIA and EIS yield similar results on the temperature, emission measure magnitude, and thermal distribution in the fans, though sometimes the AIA data suggest a relatively larger thermal width. The result is that both the Fe VIII 185.213 A and Si VII 275.368 A lines are formed at log(T{sub e} /K){approx} 5.9 in the fans, and the AIA 131 A response also shifts to this temperature.« less

Authors:
;  [1];  [2]
  1. College of Science, George Mason University, 4400 University Drive, Fairfax, VA 22020 (United States)
  2. Space Science Division, Naval Research Laboratory, Washington, DC 20375 (United States)
Publication Date:
OSTI Identifier:
21574874
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 730; Journal Issue: 2; Other Information: DOI: 10.1088/0004-637X/730/2/85
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; EMISSION; EXTREME ULTRAVIOLET RADIATION; IRON; SILICON; SOLAR CORONA; SPECTROSCOPY; TEMPERATURE DISTRIBUTION; TEMPERATURE MEASUREMENT; VELOCITY; ATMOSPHERES; ELECTROMAGNETIC RADIATION; ELEMENTS; METALS; RADIATIONS; SEMIMETALS; SOLAR ATMOSPHERE; STELLAR ATMOSPHERES; STELLAR CORONAE; TRANSITION ELEMENTS; ULTRAVIOLET RADIATION

Citation Formats

Brooks, David H., Young, Peter R., and Warren, Harry P., E-mail: dhbrooks@ssd5.nrl.navy.mil. EUV SPECTRAL LINE FORMATION AND THE TEMPERATURE STRUCTURE OF ACTIVE REGION FAN LOOPS: OBSERVATIONS WITH HINODE/EIS AND SDO/AIA. United States: N. p., 2011. Web. doi:10.1088/0004-637X/730/2/85.
Brooks, David H., Young, Peter R., & Warren, Harry P., E-mail: dhbrooks@ssd5.nrl.navy.mil. EUV SPECTRAL LINE FORMATION AND THE TEMPERATURE STRUCTURE OF ACTIVE REGION FAN LOOPS: OBSERVATIONS WITH HINODE/EIS AND SDO/AIA. United States. doi:10.1088/0004-637X/730/2/85.
Brooks, David H., Young, Peter R., and Warren, Harry P., E-mail: dhbrooks@ssd5.nrl.navy.mil. Fri . "EUV SPECTRAL LINE FORMATION AND THE TEMPERATURE STRUCTURE OF ACTIVE REGION FAN LOOPS: OBSERVATIONS WITH HINODE/EIS AND SDO/AIA". United States. doi:10.1088/0004-637X/730/2/85.
@article{osti_21574874,
title = {EUV SPECTRAL LINE FORMATION AND THE TEMPERATURE STRUCTURE OF ACTIVE REGION FAN LOOPS: OBSERVATIONS WITH HINODE/EIS AND SDO/AIA},
author = {Brooks, David H. and Young, Peter R. and Warren, Harry P., E-mail: dhbrooks@ssd5.nrl.navy.mil},
abstractNote = {With the aim of studying active region fan loops using observations from the Hinode EUV Imaging Spectrometer (EIS) and Solar Dynamics Observatory Atmospheric Imaging Assembly (AIA), we investigate a number of inconsistencies in modeling the absolute intensities of Fe VIII and Si VII lines, and address why spectroheliograms formed from these lines look very similar despite the fact that ionization equilibrium calculations suggest that they have significantly different formation temperatures: log(T{sub e} /K) = 5.6 and 5.8, respectively. It is important to resolve these issues because confidence has been undermined in their use for differential emission measure (DEM) analysis, and Fe VIII is the main contributor to the AIA 131 A channel at low temperatures. Furthermore, the strong Fe VIII 185.213 A and Si VII 275.368 A lines are the best EIS lines to use for velocity studies in the transition region, and for assigning the correct temperature to velocity measurements in the fans. We find that the Fe VIII 185.213 A line is particularly sensitive to the slope of the DEM, leading to disproportionate changes in its effective formation temperature. If the DEM has a steep gradient in the log(T{sub e} /K) = 5.6-5.8 temperature range, or is strongly peaked, Fe VIII 185.213 A and Si VII 275.368 A will be formed at the same temperature. We show that this effect explains the similarity of these images in the fans. Furthermore, we show that the most recent ionization balance compilations resolve the discrepancies in absolute intensities. With these difficulties overcome, we combine EIS and AIA data to determine the temperature structure of a number of fan loops and find that they have peak temperatures of 0.8-1.2 MK. The EIS data indicate that the temperature distribution has a finite (but narrow) width < log ({sigma}{sub Te}/K) = 5.5 which, in one detailed case, is found to broaden substantially toward the loop base. AIA and EIS yield similar results on the temperature, emission measure magnitude, and thermal distribution in the fans, though sometimes the AIA data suggest a relatively larger thermal width. The result is that both the Fe VIII 185.213 A and Si VII 275.368 A lines are formed at log(T{sub e} /K){approx} 5.9 in the fans, and the AIA 131 A response also shifts to this temperature.},
doi = {10.1088/0004-637X/730/2/85},
journal = {Astrophysical Journal},
number = 2,
volume = 730,
place = {United States},
year = {Fri Apr 01 00:00:00 EDT 2011},
month = {Fri Apr 01 00:00:00 EDT 2011}
}