No abstract

No abstract

We obtained high-resolution extreme-ultraviolet (EUV) spectra of solar active regions, quiet-Sun areas, and off-limb areas during 1991 May 7 and 1993 August 17 flights of NASA/Goddard Space FUght Center's Solar EUV Rocket Telescope and Spectrograph (SERTS). The 1991 flight was the first time a multilayer coated diffraction grating was ever used in space. Emission fines from the eight ionization stages of iron between Fe +9 (Fe x) and Fe + 16 (Fe xvn) were observed. Values of numerous density-and temperature-insensitive fine intensity ratios agree with their corresponding theoretical values.Intensity ratios among various fines originating in a common stage of ionization provide measurements of coronal electron density. Numerous density-sensitive ratios are available for Fe xm, and they yield active region density (cm -3 ) logarithms of 9.66 + 0.49 and 9.60 + 0.54 for the 1993 and 1991 flights, respectively, and a quiet-Sun density of 9.03 + 0.28 for the 1993 flight. Filling factors, calculated from the derived densities assuming a path length of 1 x 10 9 cm, range from several thousandths to nearly unity.Intensity ratios among fines originating in different ionization stages of iron yield measurements of coronal electron temperature in the isothermal approximation. The fine ratios yield temperatures ranging from 1.1 x 10 6 to 5.2 x 10 6 K for the active regions, and 1.0 x 10 6 to 2.1 x 10 6 K for the quiet Sun, depending upon the ionization stages used. The derived temperature diminishes with decreasing ionization stages. Fe xvn emission, detected in the active regions but not in the quiet areas, accounts for the higher maximum active region temperature. Derived active region temperatures are greater than their quiet-Sun counterparts for ratios that include fines from Fe xrv through Fe xvi; however, the derived active region and quiet-Sun temperatures are not statistically significantly different for line intensity ratios that involve only Fe x through Fe xm. The latter similarity in derived temperatures suggests the presence of similar thermal structures in all the areas observed, although the active regions also harbor hotter material.Differential emission measure (DEM) distributions were constructed for the active region and quiet-Sun observations obtained during both flights. The two quiet-Sun DEM curves and the 1993 active region DEM curve all show peaks between log T = 6.1 and 6.2. The 1993 active region DEM has a second peak between log T = 6.6 and 6.7, and the 1991 active region DEM has only one peak, between log T = 6.5 and 6.6. Thus, the 1993 active region DEM curve appears, in some sense, to be a composite of the quiet-Sun DEM curve and the 1991 active region DEM curve. The 1991 active region exhibited flaring activity, yielded higher fine ratio temperatures, and contained greater photospheric magnetic fields than the 1993 active region.

Abstract. We investigate the conversion of the 0.5-4 and 1-8Å soft X-ray flux measurements made by detectors on the Geostationary Operational Environmental Satellites (GOES) into temperature and emission measures of coronal plasma using modern spectral models and modern understanding of coronal abundances. In particular, the original analysis by Thomas, Starr & Crannell (1985) is updated to take into account the realization that coronal abundances may be quite different from photospheric abundances. An important result of this analysis is that the derived temperatures and emission measures depend strongly on the assumed abundances even at high temperatures where continuum rather than spectral lines dominates the Sun's X-ray spectrum. This occurs because the higher coronal abundances mean that most of the continuum is due to free-bound emission processes, not free-free emission, and thus is abundance-dependent. We find significant differences between modern calculations of the temperature response of the flux measurements and the versions currently in use: for a typical flare, emission measures may be up to a factor of 4 smaller than the current software suggests. Derived temperatures are similar for both photospheric and coronal abundances for cool flares (e.g., 15 MK), but for hot flares (e.g., 35 MK) coronal abundances can lead to significantly (∼ 25%) lower temperatures being derived.

No abstract

Goddard Space Flight CenterÏs Solar EUV Rocket Telescope and Spectrograph was Ñown on 1995 May 15 (SERTS-95), carrying a multilayer-coated toroidal di †raction grating that enhanced the instrumental sensitivity in its second-order wave band (171È225 Spectra and spectroheliograms of NOAA Ó). active region 7870 (N09 W22) were obtained in this wave band with a spectral resolution (instrumental FWHM) D30and in the Ðrst-order wave band (235È335 with a spectral resolution D55 mÓ Ó ) m Ó . Spectra and spectroheliograms of quiet-Sun areas northeast of the active region were also obtained. We derived the SERTS-95 relative radiometric calibration directly from Ñight data by means of density-and temperature-insensitive line intensity ratios. Most theoretical values for such ratios were obtained from the CHIANTI database. A total of 44 di †erent lines were used to derive the relative radiometric calibration in the two spectral orders, most of them coming from seven (Fe XÈFe XVI) of the nine (Fe IXÈ Fe XVII) observed ionization stages of iron. The resulting relatively calibrated line intensities agree well with their corresponding normalized theoretical values. This supports the overall accuracy of the atomic physics parameters and demonstrates the power of the technique. The present work extends earlier work by Brosius, Davila, & Thomas, who determined the SERTS-95 second-order response using this technique. Many of the ratios employed here can be used to carry out a similar calibration exercise on spectra from the Coronal Diagnostic Spectrometer (CDS) aboard the Solar and Heliospheric Observatory (SOHO). We placed the line intensities onto an absolute scale by forcing our quiet-Sun He II j303.8 ] Si XI j303.3 intensity to match that from previous observations. The resulting active region and quietSun absolutely calibrated line lists contain 127 and 20 lines, respectively. Active region densities derived from density-sensitive line intensity ratios of Fe X, XI, XIII, and XIV are mutually consistent with log densities derived from Fe XII are signiÐcantly greater (log n e D 9.4^0.2 ; n e D 10).

We have developed expressions which give the effective color temperatures and corresponding emission measures for solar X-ray events observed with instruments onboard any of the GOES satellites. Since 1976, these satellites have been used to monitor continuously the full-Sun X-ray emission in two broadband wavelength

No abstract