Diagnostics of Solar and Astrophysical Plasmas Dependent on Autoionization Phenomena

Doschek, G. A.

doi:10.1007/978-1-4684-4877-1_6

Cited by 20 publications

(20 citation statements)

References 185 publications

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“…The O IV j1401.16 line is signiÐcantly weaker than the Si IV line and has an electron density dependence. However, at quiet-Sun densities (e.g., Doschek et al 1998) the line is close to the low-density limit (Doschek 1985). Nevertheless, electron density e †ects probably inÑuence some of the observations, and we will describe the e †ect in°3.1.…”

Section: Discussionmentioning

confidence: 78%

The Physics of the Solar Lower Transition Region

Doschek

Mariska

2001

ApJ

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We discuss quiet-Sun intensities of spectral lines of O IV j1401.16 and Si IV j1402.77, their ratio, and their relation to expected properties of the lower solar transition region. The data consist of simultaneous measurements of the two line intensities for 16,988 pixels with spatial dimensions of 1A square obtained by the Solar Ultraviolet Measurement of Emitted Radiation spectrometer on the Solar and Heliospheric Observatory spacecraft. In ionization equilibrium, the electron temperatures of maximum concentration of the two ions are 1.6 ] 105 and 6.3 ] 104 K, respectively. Assuming ionization equilibrium, the line intensity ratio is directly proportional to the emission measure ratio between plasma at these temperatures. Thus, the observations represent 16,988 snapshots of two temperature regions of the di †erential emission measure at arcsecond spatial scales in the quiet Sun. We derive an average quietSun j1401.16/j1402.77 ratio, acquired from observations over 3 hr and a 30@@ ] 290@@ spatial region, of 0.267^0.050. The 1 p deviation of this ratio is only 20%, but it is about 2.4 times greater than expected purely from counting statistics. We also Ðnd that the ratio is about 20% smaller for the most intense features in the spectra. From analysis of another ratio, i.e., O IV j1399.77/O IV j1401.16, we argue that this decrease could be due to a higher electron density in the intense features relative to the lower intensity features. We discuss the implications of these observations for understanding the morphology of the transition region.

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Section: Discussionmentioning

confidence: 78%

The Physics of the Solar Lower Transition Region

Doschek

Mariska

2001

ApJ

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“…The material presented here builds on and updates the useful review articles on atomic processes and spectroscopic diagnostics for the solar transition region and corona that have been previously written by Dere and Mason (1981), Gabriel and Mason (1982), Doschek (1985), Mason and Monsignori Fossi (1994), Del Zanna and Mason (2013) and Bradshaw and Raymond (2014).…”

Section: Introductionmentioning

confidence: 89%

“…Some of them produced the best XUV spectra of the solar corona and transition region to date. An overview of these early days can be found in Doschek (1985), Mason and Monsignori Fossi (1994) and Wilhelm et al. (2004a).…”

Section: The Solar Xuv Spectrummentioning

confidence: 99%

Solar UV and X-ray spectral diagnostics

Zanna

Mason

2018

Living Rev Sol Phys

222

139

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X-ray and ultraviolet (UV) observations of the outer solar atmosphere have been used for many decades to measure the fundamental parameters of the solar plasma. This review focuses on the optically thin emission from the solar atmosphere, mostly found at UV and X-ray (XUV) wavelengths, and discusses some of the diagnostic methods that have been used to measure electron densities, electron temperatures, differential emission measure (DEM), and relative chemical abundances. We mainly focus on methods and results obtained from high-resolution spectroscopy, rather than broad-band imaging. However, we note that the best results are often obtained by combining imaging and spectroscopic observations. We also mainly focus the review on measurements of electron densities and temperatures obtained from single ion diagnostics, to avoid issues related to the ionisation state of the plasma. We start the review with a short historical introduction on the main XUV high-resolution spectrometers, then review the basics of optically thin emission and the main processes that affect the formation of a spectral line. We mainly discuss plasma in equilibrium, but briefly mention non-equilibrium ionisation and non-thermal electron distributions. We also summarise the status of atomic data, which are an essential part of the diagnostic process. We then review the methods used to measure electron densities, electron temperatures, the DEM, and relative chemical abundances, and the results obtained for the lower solar atmosphere (within a fraction of the solar radii), for coronal holes, the quiet Sun, active regions and flares.

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“…The physical significance of these diagnostics lies in the influence of N and T on plasma process being considered, whether thermonuclear fusion, transport coefficients, energy transport, magnetic reconnection, particle acceleration etc. Diagnostics of solar plasmas from EUV and X-ray emission lines have been extensively studied and several reviews are available (Gabriel and Jordan (1972), Dere and Mason (1981), Doschek (1985), Dwivedi (1988a) and references cited there). Density diagnostics are similar to that used by optical astronomers for deriving densities using the well known Oil lines at 3726 and 3729 ft.…”

Section: Introductionmentioning

confidence: 99%