Is There a High‐Energy Particle Population in the Quiet Solar Corona?

Abstract

A study of spectra emitted by the quiet solar corona indicates that the majority of line intensities originating in lowlying levels are consistent with isothermal plasma of $1:3 ; 10 6 K. Nevertheless, a number of line intensities and, in particular, those belonging to ions that are typical of higher temperatures are brighter than expected. We show in this paper that the excess brightness of the hotter lines may be satisfactorily accounted for by a two-Maxwellian electron distribution function. We have calculated the effects on the line intensities and ionization balance under the assumption of both single-and two-Maxwellian electron distribution functions. One Maxwellian is characterized by a temperature of about 110 eV (1:35 ; 10 6 K ). The second Maxwellian is assumed to be a high-energy component ranging in temperatures between 150 and 1000 eV, with electron fractions relative to the total electron density that vary from 0.5% to 10%. We found that a good match to the quiet-Sun intensities could be achieved by adding $5% electrons with a 300 Y 400 eV Maxwellian temperature to the cooler component at 110 eV. We also found that the calculated line intensities become inconsistent with the quiet solar corona measurements if more than 3% of a T e ¼ 500 eV plasma or more than 1% of a T e ¼ 1000 eV plasma is added to the cooler Maxwellian.

Sources of Solar Wind at Solar Minimum: Constraints from Composition Data

“…Ralchenko et al (2007) found that quiet Sun spectral lines were compatible with a two Maxwellian temperature distribution, provided that no more than 5 %, 3 %, and 1 % belonged to a second Maxwellian distribution with peak energy of 300-400, 500, and 1000 eV.…”

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

“…Instead, the spectra were consistent with multi-thermal plasma where the temperature of the second Maxwellian is at most log(T [K]) = 6.5 (Feldman, Landi, and Doschek, 2007, see Table 4 therein). Ralchenko, Feldman, and Doschek (2007) investigated the quiet Sun UV spectra of Si viii-Si xii, Ar xi-Ar xiii and Ca xiii-Ca xv ions observed by SUMER. These authors showed that these spectra are consistent with a bi-Maxwellian distribution, where the hot-temperature Maxwellian contains only a few per cent of particles.…”

The Electron Temperature of the Solar Transition Region as Derived From Eis and Sumer

“…By using the revised rate coefficient in Equation (2), the intensities of the lines used in the present work were calculated by representing the NTHE electrons with a second Maxwellian distribution with temperature T 2 , whose number of electrons is a fraction N of the total number of electrons in the plasma (0 N < 1). Using the work of Ralchenko et al (2007) as a guideline, we adopted a grid of values for both N and T 2 in order to explore these two parameters: N = 0, 0.01, 0.05, 0.1, 0.2 and log T 2 = 6.0, 6.3, 6.6, 6.9, 7.2, 7.5, and 7.8 (T in K). Figure 8 are shown for a temperature log T 2 = 6.9.…”