Emission lines of Fe XI in the 257-407 A wavelength region observed in solar spectra from EIS/Hinode and SERTS

Theoretical emission-line ratios involving Fe xi transitions in the 257-407 A wavelength range are derived using fully relativistic calculations of radiative rates and electron impact excitation cross-sections. These are subsequently compared with both long wavelength channel Extreme-Ultraviolet Imaging Spectrometer (EIS) spectra from the Hinode satellite (covering 245-291 A) and first-order observations (similar to 235-449 A) obtained by the Solar Extreme-ultraviolet Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and 276.36 A lines of Fe xi are detected in two EIS spectra, confirming earlier identifications of these features, and 276.36 A is found to provide an electron density (N-e) diagnostic when ratioed against the 257.55 A transition. Agreement between theory and observation is found to be generally good for the SERTS data sets, with discrepancies normally being due to known line blends, while the 257.55 A feature is detected for the first time in SERTS spectra. The most useful Fe xi electron density diagnostic is found to be the 308.54/352.67 intensity ratio, which varies by a factor of 8.4 between N-e = 108 and 1011 cm-3, while showing little temperature sensitivity. However, the 349.04/352.67 ratio potentially provides a superior diagnostic, as it involves lines which are closer in wavelength, and varies by a factor of 14.7 between N-e = 108 and 1011 cm-3. Unfortunately, the 349.04 A line is relatively weak, and also blended with the second-order Fe x 174.52 A feature, unless the first-order instrument response is enhanced.

VLT FORS spectra of blue supergiants in the Local Group galaxy NGC 6822

Half hour exposures using the ESO VLT/FORS1 combination at Paranal in Chile have allowed us to obtain spectra for three B supergiants in the dwarf irregular galaxy NGC 6822. The spectra have been analysed using non-LTE techniques and temperatures, gravities, helium content and abundances have been obtained. Overall the metallicity of NGC 6822 is found to lie between that of the LMC and of the SMC, in agreement with previous observations of H II regions and in contrast to the earlier findings of Massey et al. (1995). The analysis of H-alpha yields estimates of the mass-loss rates and wind momenta. These results demonstrate that significantly longer exposures with the same instruments will allow us to perform quantitative spectroscopy of blue supergiants in galaxies far beyond the Local Group.

Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiated in vacuum

Purpose: To measure action spectra for the induction of single- strand breaks (SSB) and double-strand breaks (DSB) in plasmid DNA by low-energy photons and provide estimates for the energy dependence of strand-break formation important for track-structure simulations of DNA damage.

ABSORPTION AND EMISSION-SPECTRA OF THE YBCO LASER PLUME

The plasma produced during laser ablation deposition of thin film YBCO has been studied by optical emission spectroscopy. There is evidence of increased YO band emission in the range 590-625 nm as the ambient oxygen gas pressure confining the plume is increased in the range 30-200 m Torr. Temporal profiles show that close to the target the plume is insensitive to ambient oxygen pressure. It is deduced that the optical emission here is excited by electron impact excitation. Further away from the target there is evidence that two distinct processes are at work. One is again electron excitation; the emission from this process decreases with distance because the expanding plume cools and collisions become less frequent in the expanding gas. The second is driven by oxidation of atomic species expelled at high speeds from the target. The main region of this activity is in the plume sheath where a shock front ensures heating of ambient O2 and reaction of monatomic plasma species to form oxide in an exothermic reaction. Spatial mapping of the emission demonstrates clearly how increasing oxygen gas pressure confines the plasma and enhances the emission intensity from the molecular YO species ejected from the target in a smaller region close to the target. Ba+ is observed as a dominant species only very close to (within 1 mm of) the target. Absorption spectra have been taken in an attempt to examine ground state and cool species in the plume. They reveal the quite surprising result that YO persists in the chamber for periods up to 1 msec. This suggests an explanation for the recent report of off-axis laser deposition in terms of simple condensation. Previously, quasi-ballistic transfer of material from target to substrate has been considered the only significant process.