Identification of [Fe III] in the solar ultraviolet spectrum
Solar ultraviolet spectra have been obtained with high spectral and spatial resolution using the Naval Research Laboratory's high-resolution telescope and spectrograph1 (HRTS) flown on rockets since 1975 and most recently on the Spacelab 2 Shuttle flight. Because the solar spectrum between ∼1,170 and 1,719 Å has been well observed for some years, few lines of substantial intensity remain unidentified. (See for example the recent compilation by Sandlin et al.2). The longest exposures during the first rocket flight of the HRTS, which obtained spectra with a spatial resolution of ∼ 1 arc s along the slit, of length ∼ 1 solar radius, and a spectral resolution of ∼0.05 Å, showed a number of weak emission lines at the solar limb, in particular between 1,570 and 1,600 Å (see Plates 16 and 17 in ref. 3), that could not readily be identified. Improved observations of these lines were obtained during the flight of HRTS on the Spacelab 2 Shuttle flight in July–August 1985, by making longer exposures (60,100 and 250 s). The scope of the data obtained has been described4. We have now identified the emission lines concerned as forbidden (electric quadrupole and magnetic dipole) transitions in Fe III, the first detection of these particular transitions in any source. They must now be considered potential candidates for previously unidentified lines in other low-density (Ne ≲ 1010 cm−3) astrophysical sources.
Electron impact excitation of Fe2+. I. A 17-level fine-structure calculation
A Breit-Pauli R-matrix calculation for the electron impact collision strengths of Fe2+ is reported involving transitions among the lowest 17 levels corresponding to the 3d6 5D, 3H, 3P, 3F and 3G terms. Resonance structures are elucidated for the first time. The calculated collision strengths at impact energies above the resonance region show some disagreements with those from an earlier five-term R-matrix calculation of Garstang et al. (1978) for example the 5D-3H and 3H-3P collision strengths are a factor of three larger than in the earlier calculation. The present calculation also investigates the variation of collision strengths with energy; in particular, resonances are found to enhance the thermally averaged effective collision strengths by up to 40% for transitions among the fine-structure levels of the 5D ground state. Effective collision strengths for all transitions among the 17 levels are tabulated for electron temperatures 10000 K and 20000 K.
A wind and shock model for active galactic nuclei.
The properties of active galactic nuclea (AGNs) are discussed in terms of a new supercritical wind model. A supercritical wind from a central source is decelerated in a shock at a distance of about 1 light-year from the center. This wind-shock model explains satisfactorily the overall spectrum of AGNs in the frequency range 10/sup 8/ Hz< or =..nu..< or =10/sup 25/ Hz, the specific order of the fluctuation time scales as well as the formation of the broad-line-emitting clouds.