Composition of the Solar Corona, Solar Wind, and Solar Energetic Particles

Schmelz, J. T.; Reames, D. V.; Steiger, R. von; Basu, Sarbani

doi:10.1088/0004-637x/755/1/33

Cited by 208 publications

(197 citation statements)

References 59 publications

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“…For recent reviews see, e.g. Asplund et al (2009);Lodders et al (2009);Schmelz et al (2012). A common set of "coronal" abundances used by many authors is that one of Feldman et al (1992), where the low-FIP elements are increased by a factor of about 4.…”

Section: Dem Inversion Methodsmentioning

confidence: 99%

The multi-thermal emission in solar active regions

Zanna¹

2013

A&A

159

110

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We present simultaneous SDO AIA and Hinode EIS observations of the hot cores of active regions (ARs) and assess the dominant contributions to the AIA EUV bands. This is an extension of our previous work. We find good agreement between SDO AIA, EVE and EIS observations, using our new EIS calibration and the latest EVE v.3 data. We find that all the AIA bands are multi-thermal, with the exception of the 171 and 335 Å, and provide ways to roughly estimate the main contributions directly from the AIA data. We present and discuss new atomic data for the AIA bands, showing that they are now sufficiently complete to obtain temperature information in the cores of ARs, with the exception of the 211 Å band. We found that the newly identified Fe xiv 93.61 Å line is the dominant contribution to the 94 Å band, whenever Fe xviii is not present. Three methods to estimate the Fe xviii emission in this band are presented, two using EIS and one directly from the AIA data. Fe xviii emission is often present in the cores of ARs, but we found cases where it is formed at 3 MK and not 7 MK, the temperature of peak ion abundance in equilibrium. The best EIS lines for elemental abundance determination and differential emission measure (DEM) analysis are discussed. A new set of abundances for many elements are obtained from EIS observations of hot 3 MK loops. The abundances of the elements with low first ionisation potential (FIP), relative to those of the high-FIP elements, are found to be enhanced by about a factor of three, compared to the photospheric values. A measurement of the path length implies that the absolute abundances of the low-FIP elements are higher than the photospheric values by at least a factor of three. We present a new DEM method customised for the AIA bands, to study the thermal structure of ARs at 1 resolution. This was tested on a few ARs, including one observed during the Hi-C rocket flight. We found excellent agreement between predicted and observed AIA count rates and EIS radiances. Overall we found few differences between the AIA and Hi-C 193 Å images of coronal structures, despite the higher Hi-C resolution (0.25 ). The Hi-C images and the AIA DEM modelling suggest that some of the cooler loops (below 1 MK) are already resolved by AIA, while the hotter (1.5-2.5 MK) "background" emission is in most places still unresolved even at the Hi-C resolution. This unresolved emission is significantly lower than previously observed with TRACE, the SOHO CDS, and Hinode EIS spectrometers. Its enhancement appears to be mostly due to increased iron abundance. We find an ubiquitous presence of emission at different temperatures that is not co-spatial, and suggest that future high-resolution imaging is carried out with isothermal bands.

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Section: Dem Inversion Methodsmentioning

confidence: 99%

The multi-thermal emission in solar active regions

Zanna¹

2013

A&A

159

110

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“…relative to hydrogen) coronal abundances are also still debated in the literature. In fact, it is still unclear whether the low-FIP elements are enhanced in the corona, or high FIP elements depleted, relative to their photospheric values, or if a 'hybrid' solution applies, as suggested by Schmelz et al (2012).…”

Section: Observations and Data Analysismentioning

confidence: 99%

Response of Hinode XRT to quiet Sun, active region and flare plasma

O’Dwyer¹,

Zanna²,

Mason³

2013

A&A

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Aims. We examine the response of the Hinode X-Ray Telescope (XRT), using simultaneous observations with the Hinode Extremeultraviolet Imaging Spectrometer (EIS), for a flare, an active region and a quiet Sun region. We also examine the relative intensity calibration of EIS and XRT. Methods. EIS differential emission measure distribution (DEM) curves were used to create synthetic spectra with the CHIANTI atomic database. The contribution of spectral lines and continuum emission to each of the XRT channels was determined from the synthetic spectra, which were then convolved with the effective area of each XRT channel. The predicted total count rates for each channel were compared with the observed count rates. The effects of varying elemental abundances and the temperature range for the inversion were investigated. DEMs obtained from the XRT bands were also computed and compared to those obtained with EIS.Results. For the active region observations, the observed XRT count rates for most of the channels are in reasonable agreement with those predicted using EIS observations, but are dependent on the elemental abundances chosen. Significant discrepancies between predicted and observed count rates were found and are discussed for the adjacent quiet Sun region and also for the flare. Synthetic spectra and continuum emission contributing to the XRT channels are presented and discussed for the active region, quiet Sun and flare observations.

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“…A synthetic solar flare spectrum calculated with the latest version (8.0.1) of the CHIANTI database (Dere et al 1997;Del Zanna et al 2015) with the coronal abundances of Schmelz et al (2012) indicates that Ne ix makes a contribution of less than 1 per cent to the total line flux in both instances, while solar flare observations confirm that the features are due to Fe xiv (Bhatia et al 1994) and O iv (Widing 1982). In the case of the 81.58Å transition, the predicted enhancement is too small to detect the feature, even under optimal conditions.…”

Section: Resultsmentioning

confidence: 99%

“…The description of levels is in the nl-coupled averageof-configuration approximation. We consider a mixture of H, He, Ne and Na, with the solar coronal abundances of Schmelz et al (2012). Using the nl-coupled configuration average description, GALAXY considers for Ne and Na the fully stripped ions as well as the H-like configurations 1s, 2s, 2p, 3s, 3p, 3d, .…”

Section: Line Coincidence Photopumping Modelsmentioning

confidence: 99%

X-ray line coincidence photopumping in a solar flare

Keenan

Poppenhaeger

Mathioudakis

et al. 2017

Monthly Notices of the Royal Astronomical Society

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Line coincidence photopumping is a process where the electrons of an atomic or molecular species are radiatively excited through the absorption of line emission from another species at a coincident wavelength. There are many instances of line coincidence photopumping in astrophysical sources at optical and ultraviolet wavelengths, with the most famous example being Bowen fluorescence (pumping of O iii 303.80Å by He ii), but none to our knowledge in X-rays. However, here we report on a scheme where a He-like line of Ne ix at 11.000Å is photopumped by He-like Na x at 11.003Å, which predicts significant intensity enhancement in the Ne ix 82.76Å transition under physical conditions found in solar flare plasmas. A comparison of our theoretical models with published X-ray observations of a solar flare obtained during a rocket flight provides evidence for line enhancement, with the measured degree of enhancement being consistent with that expected from theory, a truly surprising result. Observations of this enhancement during flares on stars other than the Sun would provide a powerful new diagnostic tool for determining the sizes of flare loops in these distant, spatially-unresolved, astronomical sources.

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Composition of the Solar Corona, Solar Wind, and Solar Energetic Particles

Cited by 208 publications

References 59 publications

The multi-thermal emission in solar active regions

The multi-thermal emission in solar active regions

Response of Hinode XRT to quiet Sun, active region and flare plasma

X-ray line coincidence photopumping in a solar flare

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