S XI emission lines in active region spectra obtained with the Solar EUV Rocket Telescope and Spectrograph (SERTS)

Theoretical electron density sensitive emission line ratios involving a total of eleven 2s(2)2p(2)-2s2p(3) transitions in S XI between 187 and 292 Angstrom are presented. A comparison of these with solar active region observations obtained during rocket flights by the Solar EUV Rocket Telescope and Spectrograph (SERTS) reveals generally good agreement between theory and experiment. However, the 186.87 Angstrom line is masked by fairly strong Fe XII emission at the same wavelength, while 239.83 Angstrom is blended with an unknown feature, and 285.58 Angstrom is blended with possibly N IV 285.56 Angstrom. In addition, the 191.23 Angstrom line appears to be more seriously blended with an Fe XIII feature than previously believed. The presence of several new S XI lines is confirmed in the SERTS spectra, at wavelengths of 188.66, 247.14 and 291.59 Angstrom, in excellent agreement with laboratory measurements. In particular, the detection of the 2s(2)2p(2) P- 3(1) -2s2p(3) P-3(0,1) transitions at 242.91 Angstrom is the first time (to our knowledge) that this feature has been identified in the solar spectrum. The potential usefulness of the S XI line ratios as electron density diagnostics for the solar transition region and corona is briefly discussed.

Inner-shell photoexcitation of Fe XV and Fe XVI

The configuration-interaction method as implemented in the computer code CIV3 is used to determine energy levels, electric dipole radiative transition wavelengths, oscillator strengths and transition probabilities for inner-shell excitation of transitions in Fe XV and Fe XVI. Specifically, transitions are considered of the type 1s(2) 2s(2) 2p(6) 3s(2) -1s(2) 2s(2) 2p(5) 3l3l' 3l" (l, l' and l" = s,p or d) in FeXV and 1s(2) 2s(2) 2p(6) 3s- 1s(2) 2s(2) 2p(5) 3l3l' (l and l' = s,p or d) in FeXVI, using the relativistic Breit-Pauli approach. An assessment of the accuracy of the derived atomic data is performed.

A search for circumstellar material around B-type stars in the Galactic halo

19 B-type stars, selected from the Palomar-Green Survey, have been observed at infrared wavelengths to search for possible infrared excesses, as part of an ongoing programme to investigate the nature of early-type stars at high Galactic latitudes. The resulting infrared fluxes, along with Stromgren photometry, are compared with theoretical flux profiles to determine whether any of the targets show evidence of circumstellar material, which may be indicative of post-main- sequence evolution. Eighteen of the targets have flux distributions in good agreement with theoretical predictions. However, one star, PG 2120 + 062, shows a small near-infrared excess, which may be due either to a cool companion of spectral type F5-F7, or to circumstellar material, indicating that it may be an evolved object such as a post-asymptotic giant branch star, in the transition region between the asymptotic giant branch and planetary nebula phase, with the infrared excess due to recent mass loss during giant branch evolution.

Improved data for solar flare X-ray spectral analysis

The inclusion of collisional rates for He-like Fe and Ca ions is discussed with reference to the analysis of solar flare Fe XXV and Ca XIX line emission, particularly from the Yohkoh Bragg Crystal Spectrometer (BCS). The new data are a slight improvement on calculations presently used in the BCS analysis software in that the discrepancy in the Fe XXV y and z line intensities (observed larger than predicted) is reduced. Values of electron temperature from satellite-to-resonance line ratios are slightly reduced (by up to 1 MK) for a given observed ratio. The new atomic data will be incorporated in the Yohkoh BCS databases. The data should also be of interest for the analysis of high-resolution, non-solar spectra expected from the Constellation-X and Astro-E space missions. A comparison is made of a tokamak S XV spectrum with a synthetic spectrum using atomic data in the existing software and the agreement is found to be good, so validating these data for particularly high-n satellite wavelengths close to the S XV resonance line. An error in a data file used for analyzing BCS Fe XXVI spectra is corrected, so permitting analysis of these spectra.

Dynamic tunnelling ionization of H-+(2) in intense fields

Intense-field ionization of the hydrogen molecular ion by linearly polarized light is modelled by direct solution of the fixed-nuclei time-dependent Schrodinger equation and compared with recent experiments. Parallel transitions are calculated using algorithms which exploit massively parallel computers. We identify and calculate dynamic tunnelling ionization resonances that depend on laser wavelength and intensity, and molecular bond length. Results for lambda similar to 1064 nm are consistent with static tunnelling ionization. At shorter wavelengths lambda similar to 790 nm large dynamic corrections are observed. The results agree very well with recent experimental measurements of the ion spectra. Our results reproduce the single peak resonance and provide accurate ionization rate estimates at high intensities. At lower intensities our results confirm a double peak in the ionization rate as the bond length varies.

Systematic study of visible transitions in Ti-like high Z ions

The magnetic dipole transitions between fine structure levels in the ground term of Ti-like ions, (3d(4)) D-5(2)-D-5(3), were investigated by observation of visible and near-UV light for several elements with atomic numbers from 51 to 78. The wavelengths are compared with theoretical values we recently calculated. The differences between the present calculations and measurements are less than 0.6%. The anomalous wavelength stability predicted by Feldman, Indelicato and Sugar [J. Opt. Soc. Am. B 8, 3 (1991)] was observed. We attribute this anomalous wavelength stability to the transition from LS to JJ coupling and the asymptotic behavior of the transition energies in the intermediate coupling regime.

High harmonic generation in the relativistic limit

The generation of extremely bright coherent X-ray pulses in the femtosecond and attosecond regime is currently one of the most exciting frontiers of physics - allowing, for the first time, measurements with unprecedented temporal resolution(1-6). Harmonics from laser - solid target interactions have been identified as a means of achieving fields as high as the Schwinger limit(2,7) (E = 1.3 x 10(16) V m(-1)) and as a highly promising route to high-efficiency attosecond (10(-18) s) pulses(8) owing to their intrinsically phase-locked nature. The key steps to attain these goals are achieving high conversion efficiencies and a slow decay of harmonic efficiency to high orders by driving harmonic production to the relativistic limit(1). Here we present the first experimental demonstration of high harmonic generation in the relativistic limit, obtained on the Vulcan Petawatt laser(9). High conversion efficiencies (eta> 10(-6) per harmonic) and bright emission (> 10(22) photons s(-1) mm(-2) mrad(-2) (0.1% bandwidth)) are observed at wavelengths <4 nm ( the 'water-window' region of particular interest for bio-microscopy).

Optical bistability in nonlinear surface-plasmon polaritonic crystals

Nonlinear optical transmission through periodically nanostructured metal films (surface-plasmon polaritonic crystals) has been studied. The surface polaritonic crystals have been coated with a nonlinear polymer. The optical transmission of such nanostructures has been shown to depend on the control-light illumination conditions. The resonant transmission exhibits bistable behavior with the control-light intensity. The bistability is different at different resonant signal wavelengths and for different wavelengths of the control light. The effect is explained by the strong sensitivity of the surface-plasmon mode resonances at the signal wavelength to the surrounding dielectric environment and the electromagnetic field enhancement due to plasmonic excitations at the controlled light wavelengths.

Seasonal and diurnal variations in ultraviolet-B and ultraviolet-A irradiances at and below the sea surface at Helgoland (North Sea) over a 6-year period

Ultraviolet(UV) radiation at four wavelengths (305, 320, 340 and 380 nm) and photosynthetically active radiation (PAR) were measured from May 1994 to October 1999 using Biospherical UV radiometers. A surface reference sensor located on the roof of the Marine Station at Helgoland recorded values every 5 min, and an equivalent profiling underwater sensor was used for measurements in the sea at approximately monthly intervals. The ratio of 305-nm radiation to PAR varied seasonally, with a 14-fold increase from winter to summer. A much weaker seasonal trend (ca. 1.5-fold) was apparent in the ratio of 320-nm radiation to PAR, but there was no seasonal trend in the ratios of 340- or 380-nm radiation to PAR. The year-to-year variations in 305-nm radiation were also much greater relative to PAR than for the other UV wavelengths, but there was no evidence of a change in the 305 nm:PAR ratio over the study period. The ratios of both 305- and 320-nm radiation to PAR increased from dawn to midday, but those of 340- and 380-nm radiation were almost constant through the day, except shortly before sunrise and after sunset when the proportions of 340- and 380-nm radiation increased. Underwater measurements of PAR and UV suggest that the 1% depth for 305-nm radiation was little more than 1 m, but this estimate is valid only for summer and autumn because, in other seasons, few reliable readings for 305-nm radiation could be obtained underwater, and no attenuation coefficient could be calculated. The 1% depths recorded for the other UV wavelengths in the middle 6 months of the year were 2.0 m for 320 nm, 2.6 m for 340 nm and 4.6 m for 380 nm, compared with 12 m for PAR, but the attenuation of all wavebands increased sharply in October and remained higher until March. An analysis of the influence of sun angle, total column ozone concentration, the proportion of skylight, and cloud cover on the ratio of UV wavelengths to PAR in surface irradiance demonstrated that solar angle has a greater influence than ozone concentration on the irradiance at 305 nm, and that the typical occurrence of ozone

WASP-4b: A 12th magnitude transiting hot Jupiter in the southern hemisphere

We report the discovery of WASP-4b, a large transiting gas-giant planet with an orbital period of 1.34 days. This is the first planet to be discovered by the SuperWASP-South observatory and CORALIE collaboration and the first planet orbiting a star brighter than 16th magnitude to be discovered in the southern hemisphere. A simultaneous fit to high-quality light curves and precision radial velocity measurements leads to a planetary mass of 1.22(-0.08)(+0.09) M-Jup and a planetary radius of 1.42(-0.04)(+0.07) R-Jup. The host star is USNO-B1.0 0479-0948995, a G7 V star of visual magnitude 12.5. As a result of the short orbital period, the predicted surface temperature of the planet is 1761 K, making it an ideal candidate for detections of the secondary eclipse at infrared wavelengths.

Spectroscopy of astrophysical plasmas in the laboratory

Most of the matter in the universe is in the few form of a plasma. Over the past years physicists have produced laboratory plasmas that can mimic those observed in astrophysics. The best known is probably the tokamak, which has similar physical conditions and plasma processes to those found in collisionally dominated solar and stellar transition regions and coronae. Spectroscopy of such laboratory plasmas, in, particular at, ultraviolet and X-ray wavelengths, has greatly aided our understanding of their astrophysical counterparts. More recently, experiments have been performed on the Z Machine at the Sandia National Laboratory in the USA with the aim of creating, for the first time, steady-state photoionization-dominated plasmas that recreate the conditions found in some accretion-powered X-ray sources, such as X-ray binaries. In the future, experiments are envisaged with laser-produced plasmas at AWE Aldermaston that may be able to mimic the steady-state conditions found in high-energy accretion-powered sources, including the central regions of active galaxies.

Measurements of the XUV transmission of aluminium with a soft x-ray laser

We have used XUV lasers to make absolute measurements of the photoabsorption coefficient of Al at energies just below that of the L3 absorption edge at 72.7 eV. Transmission measurements at photon energies of 53.7 and 63.3 eV have been made using Ne-like Ni and Ge XUV lasers. The XUV laser output was recorded in first and second orders using a flat-field spectrometer. Al foils with steps of various thicknesses were placed over the first order diffracted signal, while the second order diffraction was used to monitor the beam profile at each position. The transmission data agree extremely well with the original measurements at these wavelengths made by Henke and co-workers (Henke B L, Gullikson E M and Davis J C 1993 At. Data Nucl. Data Tables 54 18 1), but are in conflict with subsequent measurements which are currently in common use (Gullikson E M, Denham P, Mrowka S and Underwood J H 1994 Phys. Rev. B 49 16 283). The exact values of the absorption coefficients in this region of the spectrum have significant implications for the diagnosis of the energy and intensity output of XUV lasers.

Multiplexing Sensory Molecules Map Protons Near Micellar Membranes

Hi-fi mapping: Multiplexing fluorescent sensors that simultaneously target proton concentration and polarity move to micellar nanospaces, self-regulate their positions, and report their pKa values and wavelengths, which are controlled by their local environments. Such sensory functions enable maps of proton gradients near micellar membranes to be drawn.

Rare-earth complexes of ferrocene-containing ligands: Visible-light excitable luminescent materials

The ferrocene-derivatives bis(ferrocenyl-ethynyl)-1,10-phenanthroline (Fc(2)phen) and ferrocenoyltrifluoroacetone (Hfta) have been used to synthesize ferrocene-containing rare-earth beta-diketonate complexes. The complexes [Ln(tta)(3)(Fc(2)phen)] and [Ln(fta)(3)(phen)] (where Ln = La, Nd, Eu, Yb) show structural similarities to the tris(2-thenoyltrifluoroacetonate)(1,10-phenanthroline)lanthanide(III) complexes, [Ln(tta)(3)(phen)]. The coordination number of the lanthanide ion is 8, and the coordination sphere can be described as a distorted dodecahedron. However, the presence of the ferrocene moieties shifts the ligand absorption bands of the rare-earth complexes to longer wavelengths so that the complexes can be excited not only by ultraviolet radiation but also by visible light of wavelengths up to 420 nm. Red photoluminescence is observed for the europium(III) complexes and near-infrared photoluminescence for the neodymium(III) and ytterbium(III) complexes. The presence of the ferrocene groups makes the rare-earth complexes hydrophobic and well-soluble in apolar organic solvents.

Rare-earth nitroquinolinates: Visible-light-sensitizable near-infrared emitters in aqueous solution

Water-soluble, stable, and easily synthesizable 1:4 complexes of rare-earth ions with 8-hydroxy-5-nitroquinolinate ligands have been prepared. These complexes can be sensitized by visible light with wavelengths up to 480 nm and show near-infrared emission in aqueous solution. The incorporation of a nitro group in the quinoline moiety shifts its absorption bands to longer wavelengths and also increases its molar absorptivity by a factor of 2.5, thereby significantly enhancing its light-harvesting power. The presence of the nitro group also increases the solubility of the resulting complexes, making them water-soluble. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007.