Oscillator strengths for transitions in C-like ions between K XIV and Mn XX

Energy levels and oscillator strengths (transition probabilities) have been calculated for transitions among 46 fine-structure levels of the (1s(2)) 2s(2) 2p(2), 2s2p(3),2p(4), 2s(2)2p3s, 2s(2) 2p3p and 2s(2)2p3d configurations of C-like K XIV, Sc XVI, Ti XVII, V XVIII, Cr XIX and Mn XX using the GRASP code. Configuration interaction and relativistic effects have been included while generating the wavefunctions. Calculated values of energy levels agree within 3% with the experimentally compiled results, and the length and velocity forms of oscillator strengths agree within 20% for a majority of allowed transitions.

Identification in the Ca II K spectral region of sharp-lined B- type stars

Previous Call K observations of the B-type star HD 83206 have revealed putative high-velocity interstellar clouds (HVCs) at Local Standard of Rest (LSR) velocities of -80 and -110 km s(- 1). Similar results were also found for the sightline towards HD135485. In this article, we show that these absorption lines are in fact due tr, stellar SII features. As the Call K absorption line in B-type stars is often used to assess the presence and distance of HVCs. we also present a very high quality spectrum of HD 83206 in the Ca II K region (similar to+/-4 Angstrom or +/-300 km s(-1)), so that in the future confusion between stellar lines and HVC features may be avoided.

Ca II K observations of QSOs in the line-of-sight to the Magellanic Bridge

We describe medium-resolution spectroscopic observations taken with the ESO Multi-Mode Instrument (EMMI) in the CaII K line (lambda air = 3933.661 angstrom) towards 7 QSOs located in the line-of-sight to the Magellanic Bridge. At a spectral resolution R =lambda/Delta lambda = 6000, five of the sightlines have a signal-to-noise ( S/N) ratio of similar to 20 or higher. Definite Ca absorption due to Bridge material is detected towards 3 objects, with probable detection towards two other sightlines. Gas-phase CaII K Bridge and Milky Way abundances or lower limits for the all sightlines are estimated by the use of Parkes 21-cm H. emission line data. These data only have a spatial resolution of 14 arcmin compared with the optical observations which have milli-arcsecond resolution. With this caveat, for the three objects with sound CaII K detections, we find that the ionic abundance of CaII K relative to HI, A = log( N( CaK)/ N( HI)) for low- velocity Galactic gas ranges from - 8.3 to - 8.8 dex, with HI column densities varying from 3- 6 x 10(20) cm(-2). For Magellanic Bridge gas, the values of A are similar to 0.5 dex higher, ranging from similar to- 7.8 to - 8.2 dex, with N( HI) = 1- 5 x 1020 cm(-2). Higher values of A correspond to lower values of N( HI), although numbers are small. For the sightline towards B 0251 - 675, the Bridge gas has two different velocities, and in only one of these is CaII tentatively detected, perhaps indicating gas of a different origin or present-day characteristics ( such as dust content), although this conclusion is uncertain and there is the possibility that one of the components could be related to the Magellanic Stream. Higher signal-to-noise CaII K data and higher resolution H. data are required to determine whether A changes with N( HI) over the Bridge and if the implied difference in the metalicity of the two Bridge components towards B 0251-675 is real.

Single- and multiphoton detachment of K

Single- and multiphoton detachment rates have been calculated for K- using the R-matrix Floquet approach. Single-photon detachment rates, obtained at a laser field peak intensity of 10(9) W cm(-2), are discussed and compared with other theoretical work. Two-photon detachment rates at the same intensity have also been obtained, and similarities with results from earlier calculations for Li- and Na- are discussed. Three-photon rates are also presented at this laser intensity, and are compared and contrasted with those arising in the single-photon case, since both involve resonance structure with P-1(o) symmetry. The influence of resonances such as the 5s(2) S-1(e) doubly excited state and excitations of the residual atom are also considered.

K alpha yields from Ti foils irradiated with ultrashort laser pulses

We have studied the emission of Kalpha radiation from Ti foils irradiated with ultrashort (45 fs) laser pulses. We utilized the fundamental (800 nm) light from a Ti:sapphire laser on bare foils and foils coated with a thin layer of parylene E (CH). The focusing was varied widely to give a range of intensities from approximately 10(15)-10(19) W cm(-2). Our results show a conversion efficiency of laser to Kalpha energy of similar to 10(-4) at tight focus for both types of targets. In addition, the coated targets exhibited strong secondary peaks of conversion at large defocus, which we believe are due to modification of the extent of preformed plasma due to the dielectric nature of the plastic layer. This in turn affects the level of resonance absorption. A simple model of Kalpha production predicts a much higher conversion than seen experimentally and possible reasons for this are discussed.

Effects of plastic coating on K-alpha yield from ultra-short pulse

A study of the K-alpha radiation emitted from Ti foils irradiated with intense, similar to0.2 J, 67 fs, 800 nm laser pulses, scanning a range of intensities (similar to10(15)-10(18) W cm(-2)), is reported. The brightness of single-shot K-alpha line emission from the front of the targets is recorded. The yield from bare titanium (Ti) is compared to that from plastic (parylene-E) coated Ti. It is demonstrated that, for a defocused beam, a thin layer of plastic increases the yield.