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.
Ultraviolet spectroscopy of cool stars
A review is given of some developments in the study of UV emission-line spectra of cool stars, including the Sun, in recent years. Although early work on solar-line identifications depended heavily on compilations of energy levels from laboratory studies [ Natl. Stand. Ref. Data Ser. Natl. Bur. Stand.35 ( 1971);Natl. Bur. Stand. (U.S.) Circ.488 ( 1950, 1952)], the astrophysical spectra have also led to progress in understanding atomic systems and level excitation processes. The differences in excitation conditions among various structures in the solar atmosphere have permitted the spatial resolution of solar spectra to aid line identifications. Observations of cool low-gravity stars (giants and supergiants) with the International Ultraviolet Explorer have led to the discovery of a variety of fluorescent excitation processes, some resulting in the determination of further energy levels. Some examples of line-identification problems and excitation processes are discussed. This mutually beneficial interaction can be expected to continue when stellar spectroscopy becomes possible from the Hubble Space Telescope and from missions extending to the far-UV and soft-x-ray regions.
Long Ceramic Beam Tubes for Accelerator Magnets
The ceramic beam tubes for the fast and abort kickers and the bucker and pinger magnets used at Fermilab must meet a number of exacting requirements. The tubes must be long and sufficiently straight so as not to limit magnet design. They must have wall strength capable of withstanding the atmospheric and mechanical forces encountered during construction and operation. Vacuum tight ceramic to stainless steel transitions must be of reasonable cost; they must also withstand high temperature processing and remain vacuum tight to the 10/sup -9/ Torr range. To remove the possibility of static charge buildup each tube must have a surface coating of indium oxide applied to the inner wall. This thin coating is difficult to achieve and requires the most careful attention to detail. The methods used at Fermilab to achieve these goals are presented in this paper.