The coronal loop controversy: TRACE analysis

Schmelz, J. T.; Roames, J. K.; Nasraoui, K.

doi:10.1016/j.asr.2007.03.086

Cited by 5 publications

(10 citation statements)

References 12 publications

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“…One of the curious results from Schmelz et al (2003Schmelz et al ( , 2007 was that the 171-195 ratio always seemed A to produce a loop temperature of 1.2 MK (within uncertainties), even though the ratio should have been sensitive to a much broader temperature range. The work of Testa et al (2002) and Martens et al (2002) suggested that the answer could be attributed to multithermal plasma along the line of sight.…”

Section: Discussionmentioning

confidence: 99%

“…This second-generation analysis technique found results similar to those described above-a single temperature with no significant variations along the loop length. Schmelz et al (2003Schmelz et al ( , 2007 used several background subtraction methods to produce loops with a uniform temperature, but the 171-195 and 195-284 ratios resulted in statistically different temperature values A (1.2 and 1.8 MK, respectively) for the same pixel, indicating that the plasma along the line of sight might not be isothermal. Their temperature results were the same with and without background subtraction, and more suspiciously, the results were similar for loop pixels and for randomly selected pixels in the region, indicating that ratio analysis might not generate a physically meaningful value of temperature.…”

Section: Introductionmentioning

confidence: 99%

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Coronal Heat: Solar Loop Temperatures from TRACE Triple-Filter Data

Schmelz

Kashyap

Weber

2007

ApJ

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The Transition Region and Coronal Explorer (TRACE) has state-of-the-art spatial resolution and shows the most detailed images of coronal loops ever observed. The temperatures of these loops are primarily derived from the 171 to 195 filter ratio, with data from the third filter at 284 used by several authors to improve theÅ A precision of the derived temperatures. Most of these studies assume that the plasma is isothermal and model the loops primarily as uniform temperature structures with footpoint-dominated heating. However, these triple-filter data are insufficient to constrain the plasma temperature and cannot be used to determine the isothermality or otherwise of coronal loop structures. We show this explicitly by constructing differential emission measures with these same triple-filter data using a sophisticated Markov-chain Monte Carlo-based reconstruction algorithm. We find that these TRACE data cannot, in general, limit the temperature distribution for coronal loop plasma. In other words, many different temperature distributions (isothermal, broad, sloped, etc.) can reproduce the observed fluxes, and the TRACE coronal data alone cannot determine which of these distributions represents the actual coronal plasma.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Coronal Heat: Solar Loop Temperatures from TRACE Triple-Filter Data

Schmelz

Kashyap

Weber

2007

ApJ

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“…An important issue in the data analysis of coronal loops observations is background subtraction. Recent results ( Del Zanna & Mason 2003, Testa et al 2002, Schmelz et al 2003, Aschwanden & Nightingale 2005, Reale & Ciaravella 2006, Aschwanden et al 2008) have established the importance of separating the actual loop plasma from the diffuse foreground and background emission, that results from unresolved coronal structures and instrumental effects. The need of background subtraction arises from the presence of many overlapping bright structures and of diffuse emission, nearby or along the line of sight, as well as from stray light (DeForest et al 2009).…”

Section: Introductionmentioning

confidence: 99%

On the importance of background subtraction in the analysis of coronal loops observed with TRACE

Terzo¹,

Reale²

2010

A&A

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Aims. Using TRACE coronal observations, we compare the analysis and diagnostics of coronal loop after subtracting the background with two different and independent methods. Methods. We analyze sequences of images in the 171 Å and 195 Å filter bands of TRACE. One background subtraction method consists of considering background values obtained by interpolating between concentric strips around the analyzed loop. Another involves a pixel-to-pixel subtraction of the final image after the loop has completely faded out, used by Reale and Ciaravella. Results. We compare the emission distributions along the loop obtained with the two methods and find that they differ considerably. We also find differences in the related filter ratio and temperature profiles. In particular, the pixel-to-pixel subtraction leads to coherent diagnostics of a cooling loop. After applying the other type of subtraction, the diagnostics are much less clear.Conclusions. The background subtraction should be treated with care when analyzing a loop. The pixel-to-pixel subtraction appears to be more reliable, but its application is not always possible. Subtraction by means of interpolation between surrounding regions can produce higher systematic errors, because of intersecting structures and the large amount of subtracted emission in TRACE observations.

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“…It was found in testing that rudimentary background subtraction greatly improves the reliability and consistency of the results. It has been shown in Klimchuk et al (1992), Schmelz et al (2007) and Deforest & Gurman (1998) that a flat background subtraction can be effective, but can cause ambiguity as to the inferred width of loops. Our background subtraction consists of removing 80% of the lowest observed flux in the ARTB light curve, where 80% was chosen to accommodate the flux of the modeled loop existing below the observed noise floor.…”

Section: Background Subtractionmentioning

confidence: 99%

Modeling Active Region Transient Brightenings Observed With X-Ray Telescope as Multi-Stranded Loops

Kobelski

McKenzie

Donachie

2014

ApJ

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Strong evidence exists that coronal loops as observed in EUV and soft X-rays may not be monolithic isotropic structures, but can often be more accurately modeled as bundles of independent strands. Modeling the observed active region transient brightenings (ARTBs) within this framework allows exploration of the energetic ramifications and characteristics of these stratified structures. Here we present a simple method of detecting and modeling ARTBs observed with the Hinode X-Ray Telescope (XRT) as groups of 0-dimensional strands, which allows us to probe parameter space to understand better the spatial and temporal dependence of strand heating in impulsively heated loops. This partially automated method can be used to analyze a large number of observations to gain a statistical insight into the parameters of coronal structures including the number of heating events required in a given model to fit the observations. In this article we present the methodology, and demonstrate its use in detecting and modeling ARTBs in a sample data set from Hinode/XRT. These initial results show that in general, multiple heating events are necessary to reproduce observed ARTBs, but the spatial dependence of these heating events could not yet be established.

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The coronal loop controversy: TRACE analysis

Cited by 5 publications

References 12 publications

Coronal Heat: Solar Loop Temperatures from TRACE Triple-Filter Data

Coronal Heat: Solar Loop Temperatures from TRACE Triple-Filter Data

On the importance of background subtraction in the analysis of coronal loops observed with TRACE

Modeling Active Region Transient Brightenings Observed With X-Ray Telescope as Multi-Stranded Loops

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