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.
The Ultraviolet Spectra of Cool Star Chromospheres; Excitation Processes and Plasma Diagnostics
The advent of ultraviolet observations from space has led to rapid advances in our knowledge of the conditions in the chromospheres which surround cool stars. The solar spectrum has been studied at high spatial and spectral resolution for many years and can be used as a model for understanding the spectra of other high gravity (main sequence or dwarf) stars. The most recent spectroscopic developments in this area have come from the flights of US Naval Research Laboratory's High Resolution Telescope and Spectrograph (HRTS) on a series of rockets and on the Spacelab 2 Shuttle flight. Ultraviolet observations of other cool dwarf stars made with the International Ultraviolet Explorer (IUE) satellite have shown that their spectra are broadly similar to that of the sun and that the atomic excitation processes causing the emergent spectra are similar to those in the sun. The main requirement regarding atomic data is for electron-ion collision strengths. In contrast to the solar chromosphere and corona, where electron temperatures reach Te > 106 K, observations with IUE have shown that stars with low surface gravities have only cool chromospheres with Te 2 × 104 K. The gas density regime is also lower and the excitation of many of the ultraviolet lines is by radiative processes rather than by ion/electron collisions as in the sun. In particular, higher opacities lead to multiple photon scattering and line leakage in semi-forbidden transitions. Several cases of accidental overlap with strong emission lines of H I and O I result in fluorescent excitation of species such as S I, Fe II and CO. Quantitative analyses of such spectra are at an early stage and a wide variety of atomic rate coefficients need to be known more accurately. Further laboratory spectroscopy in the VUV would be valuable for some species.
Selective etching of InP in NaF solution
Abstract The crossing porous structure of InP has been obtained by electrochemical etching in NaF solutions. The behavior of the periodic oscillation occurs at different potential ranges for the different concentrations of solutions, and it will disappear with the concentration of the solution decreased. The scanning electron microscope (SEM) image shows that the pores have two directions on the surface and are perpendicular to each other. The two directions are assigned to [0 1 1] and [ 0 1 ¯ 1 ], respectively. The SEM image of the cross-section also shows that the two directions are assigned to [1 1 1]B and [ 1 1 ¯ 1 ¯ ]B. Both are due to the selective etching of F− ions. The crossing porous structure of InP is a very promising feature for the three-dimensional structure of III–V compound semiconductors for photonic band gap materials.