SOLAR TRANSITION REGION LINES OBSERVED BY THE
                    <i>INTERFACE REGION IMAGING SPECTROGRAPH</i>
                    : DIAGNOSTICS FOR THE O IV AND Si IV LINES

Dudík, J.; Zanna, G. Del; Dzifčáková, E.; Mason, H. E.; Golub, L.

doi:10.1088/2041-8205/780/1/l12

Cited by 58 publications

(72 citation statements)

References 41 publications

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“…The model of reconnection in the corona of Archontis & Hansteen (2014) in this way is a promising simulation to explain the type of explosive events observed in Si IV lines, but their model cannot really explain the formation of simultaneous Hα EBs, which requires a reconnection in the photosphere. In the paper of Dudík et al (2014), there is interesting information about the temperature of the formation of Si IV lines in a non-Maxwellian distribution of electrons. With a κ distribution, the temperature of the formation of Si IV can be just a chromospheric temperature and the intensity of the O IV line would be reduced, which could also explain the absence of signature of O IV in the hot explosions of Peter et al (2014).…”

Section: Discussionmentioning

confidence: 99%

Height formation of bright points observed by IRIS in Mg II line wings during flux emergence

Grubecka

Schmieder

Berlicki

et al. 2016

A&A

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Context. A flux emergence in the active region AR 111850 was observed on September 24, 2013 with the Interface Region Imaging Spectrograph (IRIS). Many bright points are associated with the new emerging flux and show enhancement brightening in the UV spectra. Aims. The aim of this work is to compute the altitude formation of the compact bright points (CBs) observed in Mg II lines in the context of searching Ellerman bombs (EBs). Methods. IRIS provided two large dense rasters of spectra in Mg II h and k lines, Mg II triplet, C II and Si IV lines covering all the active region and slit jaws in the two bandpasses (1400 Å and 2796 Å) starting at 11:44 UT and 15:39 UT, and lasting 20 min each. Synthetic profiles of Mg II and Hα lines are computed with non-local thermodynamic equlibrium (NLTE) radiative transfer treatment in 1D solar atmosphere model including a hotspot region defined by three parameters: temperature, altitude, and width. Results. Within the two IRIS rasters, 74 CBs are detected in the far wings of the Mg II lines (at +/−1 Å and 3.5 Å). Around 10% of CBs have a signature in Si IV and CII. NLTE models with a hotspot located in the low atmosphere were found to fit a sample of Mg II profiles in CBs. The Hα profiles computed with these Mg II CB models are consistent with typical EB profiles observed from ground based telescopes e.g. THEMIS. A 2D NLTE modelling of fibrils (canopy) demonstrates that the Mg II line centres can be significantly affected but not the peaks and the wings of Mg II lines. Conclusions. We conclude that the bright points observed in Mg II lines can be formed in an extended domain of altitudes in the photosphere and/or the chromosphere (400 to 750 km). Our results are consistent with the theory of heating by Joule dissipation in the atmosphere produced by magnetic field reconnection during flux emergence.

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Section: Discussionmentioning

confidence: 99%

Height formation of bright points observed by IRIS in Mg II line wings during flux emergence

Grubecka

Schmieder

Berlicki

et al. 2016

A&A

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“…Previous work has demonstrated that some lines such as those from Si iv can be enhanced relative to the O iv lines by factors of five or more, compared to the expected ratios in equilibrium conditions (e.g., Doyle and Raymond, 1984;Judge et al, 1995;Curdt et al, 2001;Yan et al, 2015), compared to other lines such as O iv formed at similar temperatures, assuming equilibrium conditions. Dudík et al (2014b) showed that, using a Maxwellian distribution and typical transition-region DEMs, the O iv 1401.16Å line should be stronger than the neighbouring Si iv line at 1402.77Å if photospheric abundances are considered. Using coronal abundances would increase the predicted Si iv line by a factor of 3-4, which is still not enough to explain the observed spectra.…”

Section: Diagnostics From Transition Region Linesmentioning

confidence: 99%

Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

et al. 2017

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We review the presence and signatures of the non-equilibrium processes, both non-Maxwellian distributions and non-equilibrium ionization, in the solar transition region, corona, solar wind, and flares. Basic properties of the non-Maxwellian distributions are described together with their influence on the heat flux as well as on the rates of individual collisional processes and the resulting optically thin synthetic spectra. Constraints on the presence of highenergy electrons from observations are reviewed, including positive detection of non-Maxwellian distributions in the solar corona, transition region, flares, and wind. Occurrence of non-equilibrium ionization is reviewed as well, especially in connection to hydrodynamic and generalized collisional-radiative modelling. Predicted spectroscopic signatures of non-equilibrium ionization depending on the assumed plasma conditions are summarized. Finally, we discuss the future remote-sensing instrumentation that can be used for detection of these non-equilibrium phenomena in various spectral ranges.

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“…We examined two such pairs and their ratios: the line pair 1 at 1401 Å and 1404 Å, and the line pair 2 at 1399 Å and 1404 Å. These lines and their ratios are in principle sensitive to non-Maxwellian velocity distributions (Dudík et al 2014); however, we ignore such Fig. 2d by a yellow rectangle, and that fully encloses one of the footpoints of the coronal loops rooted in the umbra.…”

Section: Density and Temperature Estimatesmentioning

confidence: 99%

A closer look at a coronal loop rooted in a sunspot umbra

Chitta

Peter

Young

2016

A&A

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Context. Extreme UV (EUV) and X-ray loops in the solar corona connect regions of enhanced magnetic activity, but they are not usually rooted in the dark umbrae of sunspots because the strong magnetic field found there suppresses convection. This means that the Poynting flux of magnetic energy into the upper atmosphere is not significant within the umbra as long as there are no light bridges or umbral dots. Aims. Here we report a rare observation of a coronal loop rooted in the dark umbra of a sunspot without any traces of light bridges or umbral dots. This allows us to investigate the loop without much confusion from background or line-of-sight integration effects. Methods. We used the slit-jaw images and spectroscopic data from the Interface Region Imaging Spectrograph (IRIS) and concentrate on the line profiles of O iv and Si iv that show persistent strong redshifted components in the loop rooted in the umbra. Using the ratios of O iv, we can estimate the density and thus investigate the mass flux. The coronal context and temperature diagnostics of these observations is provided through the EUV channels of the Atmospheric Imaging Assembly (AIA). Results. The coronal loop, embedded within cooler downflows, hosts supersonic downflows. The speed of more than 100 km s −1 is on the same order of magnitude in the transition region lines of O iv and Si iv, and is even seen at comparable speed in the chromospheric Mg ii lines. At a projected distance of within 1 of the footpoint, we see a shock transition to smaller downflow speeds of about 15 km s −1 being consistent with mass conservation across a stationary isothermal shock. Conclusions. We see no direct evidence for energy input into the loop because the loop is rooted in the dark uniform part of the umbra with no light bridges or umbral dots near by. Thus one might conclude that we are seeing a siphon flow driven from the footpoint at the other end of the loop. However, for a final result data of similar quality at the other footpoint are needed, but this is too far away to be covered by the IRIS field of view.

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SOLAR TRANSITION REGION LINES OBSERVED BY THE INTERFACE REGION IMAGING SPECTROGRAPH : DIAGNOSTICS FOR THE O IV AND Si IV LINES

Cited by 58 publications

References 41 publications

Height formation of bright points observed by IRIS in Mg II line wings during flux emergence

Height formation of bright points observed by IRIS in Mg II line wings during flux emergence

Nonequilibrium Processes in the Solar Corona, Transition Region, Flares, and Solar Wind (Invited Review)

A closer look at a coronal loop rooted in a sunspot umbra

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