Elemental abundances and temperatures of quiescent solar active region cores from X-ray observations

Zanna, G. Del; Mason, H. E.

doi:10.1051/0004-6361/201423471

Cited by 60 publications

(51 citation statements)

References 56 publications

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“…This has been identified from Hinode and SDO data (Reale et al 2009;Schmelz et al 2009;Testa & Reale 2012), and retrospectively from data obtained by the X-Ray Polychrometer instrument flown on the Solar Maximum Mission (Del Zanna & Mason 2014). While characterizing this emission is difficult (e.g., Testa et al 2011;Winebarger et al 2012), a similar scaling, EM∝T −b has been claimed (e.g., Warren et al 2012), with b of order 7-10, though Del Zanna & Mason find larger values.…”

Section: Introductionmentioning

confidence: 94%

Inference of Heating Properties From “Hot” Non-Flaring Plasmas in Active Region Cores. I. Single Nanoflares

Barnes

Cargill

Bradshaw

2016

ApJ

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The properties that are expected of "hot" non-flaring plasmas due to nanoflare heating in active regions are investigated using hydrodynamic modeling tools, including a two-fluid development of the Enthalpy Based Thermal Evolution of Loops code. Here we study a single nanoflare and show that while simple models predict an emission measure distribution extending well above 10 MK, which is consistent with cooling by thermal conduction, many other effects are likely to limit the existence and detectability of such plasmas. These include: differential heating between electrons and ions, ionization non-equilibrium, and for short nanoflares, the time taken for the coronal density to increase. The most useful temperature range to look for this plasma, often called the "smoking gun" of nanoflare heating, lies between 10 6.6 and 10 7 K. Signatures of the actual heating may be detectable in some instances.

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Section: Introductionmentioning

confidence: 94%

Inference of Heating Properties From “Hot” Non-Flaring Plasmas in Active Region Cores. I. Single Nanoflares

Barnes

Cargill

Bradshaw

2016

ApJ

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“…A re-analysis of these observations of quiescent ARs suggests that the slope of the differential emission measure (DEM) at temperatures above 10 6.7 K can be extremely steep [54]. [34] to simulate the high-temperature emission in 15 solar ARs as a function of time.…”

Section: (B) High-temperature Non-flaring Coronal Plasmasmentioning

confidence: 99%

Modelling nanoflares in active regions and implications for coronal heating mechanisms

Cargill

Warren

Bradshaw

2015

Phil. Trans. R. Soc. A.

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Recent observations from the Hinode and Solar Dynamics Observatory spacecraft have provided major advances in understanding the heating of solar active regions (ARs). For ARs comprising many magnetic strands or sub-loops heated by small, impulsive events (nanoflares), it is suggested that (i) the time between individual nanoflares in a magnetic strand is 500–2000 s, (ii) a weak ‘hot’ component (more than 10 6.6 K) is present, and (iii) nanoflare energies may be as low as a few 10 23 ergs. These imply small heating events in a stressed coronal magnetic field, where the time between individual nanoflares on a strand is of order the cooling time. Modelling suggests that the observed properties are incompatible with nanoflare models that require long energy build-up (over 10 s of thousands of seconds) and with steady heating.

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“…This is because the emission from a given atomic transition is proportional to the number of the line-emitting ion of its element. Numerous studies have shown that coronal plasmas exhibit a first ionization potential (FIP) effect (e.g., Pottasch 1963;Meyer 1985;Sheeley 1995;Raymond et al 2001 andreferences therein, Meyer 1985;Sheeley 1995;Raymond et al 2001;Ko et al 2002;Baker et al 2013;Del Zanna & Mason 2014;Brooks et al 2015;Laming 2015) in which the abundance of elements with FIPs less than around 10 eV ("low-FIP" elements) is enhanced relative to those with FIPs greater than 10 eV ("high-FIP" element), as compared to their photospheric values. The FIP bias (defined by the abundance ratio of a low-FIP element to a high-FIP element relative to its photospheric ratio) was found to vary among different solar structures.…”

Section: Introductionmentioning

confidence: 99%

Correlation of Coronal Plasma Properties and Solar Magnetic Field in a Decaying Active Region

Young

Muglach

et al. 2016

ApJ

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We present the analysis of a decaying active region observed by the EUV Imaging Spectrometer on Hinode during 2009 December 7-11. We investigated the temporal evolution of its structure exhibited by plasma at temperatures from 300,000 to 2.8 million degrees, and derived the electron density, differential emission measure, effective electron temperature, and elemental abundance ratios of Si/S and Fe/S (as a measure of the First Ionization Potential (FIP) Effect). We compared these coronal properties to the temporal evolution of the photospheric magnetic field strength obtained from the Solar and Heliospheric Observatory Michelson Doppler Imager magnetograms. We find that, while these coronal properties all decreased with time during this decay phase, the largest change was at plasma above 1.5 million degrees. The photospheric magnetic field strength also decreased with time but mainly for field strengths lower than about 70 Gauss. The effective electron temperature and the FIP bias seem to reach a "basal" state (at 1.5 × 10 6 K and 1.5, respectively) into the quiet Sun when the mean photospheric magnetic field (excluding all areas <10 G) weakened to below 35 G, while the electron density continued to decrease with the weakening field. These physical properties are all positively correlated with each other and the correlation is the strongest in the high-temperature plasma. Such correlation properties should be considered in the quest for our understanding of how the corona is heated. The variations in the elemental abundance should especially be considered together with the electron temperature and density.

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Elemental abundances and temperatures of quiescent solar active region cores from X-ray observations

Cited by 60 publications

References 56 publications

Inference of Heating Properties From “Hot” Non-Flaring Plasmas in Active Region Cores. I. Single Nanoflares

Inference of Heating Properties From “Hot” Non-Flaring Plasmas in Active Region Cores. I. Single Nanoflares

Modelling nanoflares in active regions and implications for coronal heating mechanisms

Correlation of Coronal Plasma Properties and Solar Magnetic Field in a Decaying Active Region

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