Dielectronic recombination in highly charged He-like ions

We have determined resonant strengths of the KLn (2 less than or equal to n less than or equal to 5) resonances for helium-like Ti ions and (3 less than or equal to n less than or equal to 5) resonances for helium-like Fe ions. The results were obtained using the Tokyo electron beam ion trap. Characteristic X-rays from both dielectronic recombination and radiative recombination were detected as the electron beam energy was scanned through the resonances. (C) 2003 Elsevier Science B.V. All rights reserved.

Measurements of absolute, single charge-exchange cross sections of H+, He+ and He2+ with H2O and CO2

Absolute measurements have been made of single-electron charge-exchange cross sections of H+, He+, and He2+ in H2O and CO2 in the energy range 0.3-7.5 keV amu(-1). Collisions of this type occur in the interaction of solar wind ions with cometary gases and have been observed by the Giotto spacecraft using the Ion Mass Spectrometer/High Energy Range Spectrometer (IMS/HERS) during a close encounter with comet Halley in 1986. Increases in the He+ ion density, and in the He2+ to H+ density ratio were reported by Shelley et al, and Fuselier et al. and were explained by charge exchange. However, the lack of reliable cross sections for this process made interpretation of the data difficult. New cross sections are presented and discussed in relation to the Giotto observations.

RCS CONTROL USING CASCADED CIRCULARLY POLARIZED FREQUENCY SELECTIVE SURFACES AND AN AMC STRUCTURE AS A SWITCHABLE TWIST POLARIZER

This article presents a cascaded arrangement comprising a double-layer frequency selective surface circularly polarizing (CPFSS) and a second screen that can be switched between artificial magnetic conduction (AMC) or perfect electric conducting. (PEC) states. The CPFSS consists of two stacked aluminium sheets patterned with periodic split ring structures While the AMC is a PCB sheet patterned with metallic squares interconnected by links By either open or short circuiting these links it is shown that the cascade of screens can be made to twist, or not to twist, an incident 45 degrees linearly polirized signal through 90 degrees upon reflection from the assembly The system was designed and optimized using CST software and predictions were validated experimentally and measured monostatic reflection loss results (C) 2010 Wiley Periodicals, Inc Microwave Opt Technol Lett 52 577-580, 2010. Published online in Wiley InterScience (www.interscience.wiley.com) DOI 10.1002/mop.24979

Relativistically correct hole-boring and ion acceleration by circularly polarized laser pulses

The problem of the 'hole-boring' (HB)-type of radiation pressure acceleration of ions by circularly polarized laser pulses interacting with overdense plasmas is considered in the regime where the dimensionless scaling parameter I/rho c(3) becomes large. In this regime a non-relativistic treatment of the 'HB' problem is no longer adequate. A new set of fully relativistic formulae for the mean ion energy and 'HB' velocity is derived and validated against one-dimensional particle-in-cell simulations. It is also found that the finite acceleration time of the ions results in large energy spreads in the accelerated ion beam even under the highly idealized conditions of constant laser intensity and uniform mass density.

Massive stars exploding in a He-rich circumstellar medium - III. SN 2006jc: infrared echoes from new and old dust in the progenitor CSM

We present near- (NIR) and mid-infrared (MIR) photometric data of the Type Ibn supernova (SN) 2006jc obtained with the United Kingdom Infrared Telescope (UKIRT), the Gemini North Telescope and the Spitzer Space Telescope between days 86 and 493 post-explosion. We find that the IR behaviour of SN 2006jc can be explained as a combination of IR echoes from two manifestations of circumstellar material. The bulk of the NIR emission arises from an IR echo from newly condensed dust in a cool dense shell (CDs) produced by the interaction of the ejecta Outward shock with a dense shell of circumstellar material ejected by the progenitor in a luminous blue variable (LBV)-like outburst about two years prior to the SN explosion. The CDs dust mass reaches a modest 3.0 x 10(-4) M-circle dot by day 230. While dust condensation within a CDs formed behind the ejecta inward shock has been proposed before for one event (SN 1998S), SN 2006jc is the first one showing evidence for dust condensation in a CDs formed behind the ejecta outward shock in the circumstellar material. At later epochs, a substantial and growing contribution to the IR fluxes arises from an IR echo from pre-existing dust in the progenitor wind. The mass of the pre-existing circumstellar medium (CSM) dust is at least similar to 8 x 10(-3) M-circle dot. This paper therefore adds to the evidence that mass-loss from the progenitors of core-collapse SNe could be a major source of dust in the Universe. However, yet again, we see no direct evidence that the explosion of an SN produces anything other than a very modest amount of dust.

Optical and infrared spectroscopy of the type IInSN1998S: days 3-127

We present contemporary optical and infrared spectroscopic observations of the type IIn SN 1998S covering the period between 3 and 127 days after discovery. During the first week the spectra are characterized by prominent broad H, He and C III/N III emission lines with narrow peaks, superimposed on a very blue continuum (T similar to 24 000 K). In the following two weeks the C III/N III emission vanished, together with the broad emission components of the H and He lines. Broad, blueshifted absorption components appeared in the spectra. The temperature of the continuum also dropped to similar to 14000 K. By the end of the first month the spectrum comprised broad, blueshifted absorptions in H, He, Si II, Fe II and Sc II. By day 44, broad emission components in H and He reappeared in the spectra. These persisted to as late as days similar to 100-130, becoming increasingly asymmetric. We agree with Leonard et al. that the broad emission lines indicate interaction between the ejecta and circumstellar material (CSM) emitted by the progenitor. We also agree that the progenitor of SN 1998S appears to have gone through at least two phases of mass-loss, giving rise to two CSM zones. Examination of the spectra indicates that the inner zone extended to less than or equal to 90 au, while the outer CSM extended from 185 an to over 1800 au.

Fluorescence yields for 3lnl′ Rydberg series in ions belonging to the He isoelectronic sequence

Fluorescence yields are reported for 3lnl' Rydberg series members in He-like ions of N, O and Ne. Results are presented for singlet series members with n values between 3 and 9, i.e. up to the region of overlap with the states belonging to the 4l4l' manifold in these atoms. This data is required, for example, for the interpretation of charge-exchange experiments involving bare N, O and Ne nuclei. Fluorescence yields, averaged over all 3lnl' singlet states, larger than 50% are obtained from about n = 7.

Electronic stopping power of H and He in Al and LiF from first principles

Non-linearities in the electronic stopping power of light projectiles in bulk Al and LiF are addressed from first principles using time-evolving time-dependent density functional theory. In the case of Al, the agreement of the calculations with experiments for H and He projectiles is fair, but a recently observed transition for He from one value of the electronic friction coefficient to a higher value at v ~ 0.3 a.u. is not reproduced by the calculations. For LiF, better accuracy is obtained as compared with previously published simulations, albeit the threshold remains overestimated. © 2013 Elsevier B.V.

Radiation-Pressure Acceleration of Ion Beams Driven by Circularly Polarized Laser Pulses

We present experimental studies on ion acceleration from ultrathin diamondlike carbon foils irradiated by ultrahigh contrast laser pulses of energy 0.7 J focused to peak intensities of 5×1019  W/cm2. A reduction in electron heating is observed when the laser polarization is changed from linear to circular, leading to a pronounced peak in the fully ionized carbon spectrum at the optimum foil thickness of 5.3 nm. Two-dimensional particle-in-cell simulations reveal that those C6+ ions are for the first time dominantly accelerated in a phase-stable way by the laser radiation pressure.

X-shooting Herbig Ae/Be stars: Accretion probed by near-infrared He I emission

The Herbig Ae/Be stars are intermediate mass pre-main sequence stars that bridge the gap between the low mass T Tauri stars and the Massive Young Stellar Objects. In this mass range, the acting star forming mechanism switches from magnetically controlled accretion to an as yet unknown mechanism, but which is likely to be direct disk accretion onto the star. We observed a large sample of Herbig Ae/Be stars with X-shooter to address this issue from a multi-wavelength perspective. It is the largest such study to date, not only because of the number of objects involved, but also because of the large wavelength coverage from the blue to the near-infrared. This allows many accretion diagnostics to be studied simultaneously. By correlating the various properties with mass, temperature and age, we aim to determine where and whether the magnetically controlled mass accretion mechanism halts and the proposed direct disk accretion takes over. Here, we will give an overview of the background, present some observations and discuss our initial results. We will introduce a new accretion diagnostic for the research of Herbig Ae/Be stars, the HeI 1.083 µm line. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

PS1-12sk is a Peculiar Supernova From a He-rich Progenitor System in a Brightest Cluster Galaxy Environment

We report on our discovery and observations of the Pan-STARRS1 supernova (SN) PS1-12sk, a transient with properties that indicate atypical star formation in its host galaxy cluster or pose a challenge to popular progenitor system models for this class of explosion. The optical spectra of PS1-12sk classify it as a Type Ibn SN (c.f. SN 2006jc), dominated by intermediate-width (3x10^3 km/s) and time variable He I emission. Our multi-wavelength monitoring establishes the rise time dt = 9-23 days and shows an NUV-NIR SED with temperature > 17x10^3 K and a peak rise magnitude of Mz = -18.9 mag. SN Ibn spectroscopic properties are commonly interpreted as the signature of a massive star (17 - 100 M_sun) explosion within a He-enriched circumstellar medium. However, unlike previous Type Ibn supernovae, PS1-12sk is associated with an elliptical brightest cluster galaxy, CGCG 208-042 (z = 0.054) in cluster RXC J0844.9+4258. The expected probability of an event like PS1-12sk in such environments is low given the measured infrequency of core-collapse SNe in red sequence galaxies compounded by the low volumetric rate of SN Ibn. Furthermore, we find no evidence of star formation at the explosion site to sensitive limits (Sigma Halpha