ACTIVE REGION LOOPS:<i>HINODE</i>/EXTREME-ULTRAVIOLET IMAGING SPECTROMETER OBSERVATIONS

Tripathi, Durgesh; Mason, H. E.; Dwivedi, B. N.; Zanna, G. Del; Young, Peter R.

doi:10.1088/0004-637x/694/2/1256

Cited by 140 publications

(186 citation statements)

References 45 publications

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“…It can be clearly seen that the low temperature emission is better defined in discrete structures than the high temperature emission. This has been observed previously by Tripathi et al (2009). The diffuse background emission seen in the coronal ions Fe X−Fe XIV is real and not a function of the way the data are displayed.…”

Section: Observations and Data Analysissupporting

confidence: 74%

Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region

O’Dwyer¹,

Zanna²,

Mason³

et al. 2010

A&A

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Aims. We investigate the electron density and temperature structure of a limb active region. Methods. We have carried out a study of an active region close to the solar limb using observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) and the X-ray telescope (XRT) on board Hinode. The electron density and temperature distributions of the coronal emission have been determined using emission line intensity ratios. Differential emission measure (DEM) analysis and the emission measure (EM) loci technique were used to examine the thermal structure of the emitting plasma as a function of distance from the limb. Results. The highest temperature and electron density values are found to be located in the core of the active region, with a peak electron number density value of 1.9 × 10 10 cm −3 measured using the Fe XII 186.887 Å to 192.394 Å line intensity ratio. The plasma along the line of sight in the active region was found to be multi-thermal at different distances from the limb. The EIS and XRT DEM analyses appear to be in agreement in the temperature interval from log T = 6.5−6.7. Conclusions. Our results provide new constraints for models of coronal heating in active regions.

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Section: Observations and Data Analysissupporting

confidence: 74%

Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region

O’Dwyer¹,

Zanna²,

Mason³

et al. 2010

A&A

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“…It has also been known for some time that the corona appears "fuzzier" at higher temperatures. (Tripathi et al 2009) showed that this was not simply an instrumental feature. This effect makes it very difficult to resolve a single isolated loop structure in the core of an active region.…”

Section: Introductionmentioning

confidence: 99%

“…With high spatial resolution instruments such as TRACE, and the Extremeultraviolet Imaging Spectrometer (EIS; Culhane et al 2007) onboard Hinode (Kosugi et al 2007), the warm loops seem to be spatially well resolved. Using TRACE and EIS observations the plasma parameters (such as electron density, temperature and flows) in warm loops can be measured (see e.g., Warren et al 2008a;Tripathi et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Active region moss

Tripathi¹,

Mason²,

Zanna³

et al. 2010

A&A

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Context. Active region moss are transition region phenomena, first noted in the images recorded by the Transition Region and Coronal Explorer (TRACE) in λ171. Moss regions are thought to be the footpoints of hot loops (3-5 MK) seen in the core of active regions. These hot loops appear "fuzzy" (unresolved). Therefore, it is difficult to study the physical plasma parameters in individual hot core loops and hence their heating mechanisms. Moss regions provide an excellent opportunity to study the physics of hot loops. In addition, they allow us to study the transition region dynamics in the footpoint regions. Aims. To derive the physical plasma parameters such as temperature, electron density, and filling factors in moss regions and to study their variation over a short (an hour) and a long time period (5 consecutive days). Methods. Primarily, we have analyzed spectroscopic observations recorded by the Extreme-ultraviolet Imaging Spectrometer (EIS) aboard Hinode. In addition we have used supplementary observations taken from TRACE and the X-Ray Telescope (XRT) aboard Hinode.Results. The moss emission is strongest in the Fe xii and Fe xiii lines. Based on analyses using line ratios and emission measure we found that moss regions have a characteristic temperature of log T [K] = 6.2. The temperature structure in moss region remains almost identical from one region to another and it does not change with time. The electron densities measured at different locations in the moss regions using Fe xii ratios are about 1-3 × 10 10 cm −3 and about 2-4 × 10 9 cm −3 using Fe xiii and Fe xiv. The densities in the moss regions are similar in different places and show very little variation over short and long time scales. The derived electron density substantially increased (by a factor of about 3-4 or even more in some cases) when a background subtraction was performed. The filling factor of the moss plasma can vary between 0.1-1 and the path length along which the emission originates is from a few 100 to a few 1000 kms long. By combining the observations recorded by TRACE, EIS and XRT, we find that the moss regions correspond to the footpoints of both hot and warm loops.

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“…There is evidence that the warm loops are multistranded structures impulsively heated by storms of nanoflares (Warren et al 2003;Klimchuk 2006Klimchuk , 2009Tripathi et al 2009;Ugarte-Urra et al 2009). …”

Section: Introductionmentioning

confidence: 99%

“…Because of the unresolved nature of hot coronal loops (Tripathi et al 2009) it is not possible to isolate a single loop and study its characteristics. One of the alternatives is to study the footpoints of the hot coronal loops, in the so-called "moss" areas.…”

Section: Introductionmentioning

confidence: 99%

Doppler shift of hot coronal lines in a moss area of an active region

Dadashi

Teriaca

Tripathi

et al. 2012

A&A

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The moss is the area at the footpoint of the hot (3 to 5 MK) loops forming the core of the active region where emission is believed to result from the heat flux conducted down to the transition region from the hot loops. Studying the variation of Doppler shift as a function of line formation temperatures over the moss area can give clues on the heating mechanism in the hot loops in the core of the active regions. We investigate the absolute Doppler shift of lines formed at temperatures between 1 MK and 2 MK in a moss area within active region NOAA 11243 using a novel technique that allows determining the absolute Doppler shift of EUV lines by combining observations from the SUMER and EIS spectrometers. The inner (brighter and denser) part of the moss area shows roughly constant blue shift (upward motions) of 5 km s −1 in the temperature range of 1 MK to 1.6 MK. For hotter lines the blue shift decreases and reaches 1 km s −1 for Fe xv 284 Å (∼2 MK). The measurements are discussed in relation to models of the heating of hot loops.The results for the hot coronal lines seem to support the quasi-steady heating models for nonsymmetric hot loops in the core of active regions.

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ACTIVE REGION LOOPS:HINODE/EXTREME-ULTRAVIOLET IMAGING SPECTROMETER OBSERVATIONS

Cited by 140 publications

References 45 publications

Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region

Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region

Active region moss

Doppler shift of hot coronal lines in a moss area of an active region

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