EUV Spectra of the Full Solar Disk: Analysis and Results of the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS)

Abstract

We analyze EUV spectra of the full solar disk from the Cosmic Hot Interstellar Plasma Spectrometer (CHIPS) spanning a period of two years. The observations were obtained via a fortuitous off-axis light path in the 140 -275 Å passband. The general appearance of the spectra remained relatively stable over the two-year time period, but did show significant variations of up to 25% between two sets of Fe lines that show peak emission at 1 MK and 2 MK. The variations occur at a measured period of 27.2 days and are caused by regions of hotter and cooler plasma rotating into, and out of, the field of view. The CHI-ANTI spectral code is employed to determine plasma temperatures, densities, and emission measures. A set of five isothermal plasmas fit the full-disk spectra well. A 1 -2 MK plasma of Fe contributes 85% of the total emission in the CHIPS passband. The standard Differential Emission Measures (DEMs) supplied with the CHIANTI package do not fit the CHIPS spectra well as they over-predict emission at temperatures below log 10 T = 6.0 and above log 10 T = 6.3. The results are important for cross-calibrating TIMED, SORCE, SOHO/EIT, and CDS/GIS, as well as the recently launched Solar Dynamics Observatory.

Prominence Cavity Regions Observed Using SWAP 174 Å Filtergrams and Simultaneous Eclipse Flash Spectra

“…The intensity ratio increases abruptly near the prominence edge, where the P-C region is located, by a factor 2 over a distance of 10 Mm. This needs to be compared with the surrounding cavity, observed with SWAP/Proba2 in the Fe IX/X line at 174A (see Figure 2), where the temperature reaches 0.6 to 1 MK (Sirk et al 2010). Surprisingly, the SWAP image also shows, at small scale, some coronal emission near prominence 2, with the dark cavity around.…”

“…These observations also yield relatively new results on the determination of the electron densities inside prominences when compared to previous photographic ground-based coronagraphic filtergram observations in the D3 line, where the continuum, at the location of the prominences, was not precisely measured (see Kubota and Leroy, 1970 for Lyotcoronagraph observations and Koutchmy, Lebecq and Stellmacher 1983 for eclipse broadband observations). On flash spectra, measuring the continuum outside prominences, allows us to study the electron density of the cavity and compare with the Proba 2/SWAP (Sun Watcher with APS detectors and image Processing) EUV filtergrams, dominantly recording the Fe IX/X coronal lines (Sirk et al 2010). SWAP is the main instrument of the Proba 2 mission (Project for OnBord Autonomy), see Berghmans et al 2006, Defise et al 2007, and Halain et al 2010 for a description of the SWAP parameters (see De Groof et al 2008a and2008b for the CMOS-APS imaging detectors).…”

Solar EUV Spectrum Calculated for Quiet Sun Conditions

“…For the coronal structure the temperature gradient has been derived by semi-empirically adjusting temperature values from eclipse observations by Singh, Saxena, and Bappu (1982). The density values are extended from the TR to the corona based on the values given by Doschek (1997).…”

“…The most well-known models are the CHIANTI models of differential emission measures (Dere et al, 1997;Landi et al, 2006, DEMs) which allow calculation of the optically thin emissions of the quiet and active corona, and coronal holes. Sirk, Hurwitz, and Marchant (2010) follow this approach, but use a set of isothermal plasmas in order to reproduce observations of the quiet Sun. However, the approach using DEMs is limited to modeling the pure optically thin emissions from the corona.…”

High-Resolution Laboratory Measurements and Identification of Fe IX Lines near 171 Å

“…Emission from Fe IX have been observed in laboratory plasmas, for example, those produced in magnetic fusion devices [1][2][3][4], and in space plasmas, for example, in stellar coronae, including the Sun [5][6][7][8][9][10]. The strongest Fe IX line in the extreme ultraviolet wavelength band is situated at 171 Å and is well known.…”