bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laboratory Astrophysics Experiments in X-Ray Transfer Physics Relevant to Cosmic Accretion-Powered Sources
Authors: Kahn S.M. , Craig W. , Schachter J. , Wargelin B. , Kapteyn H. , Falcone R.W. , Hettrick M.C. , London R.A. , Lee R.W. 
Published: July 2016

AbstractThe interpretation of upcoming cosmic soft X-ray spectroscopic observations may require a vast improvement in the state of our knowledge of basic atomic physics and radiation transfer processes, particularly for the important class of accretion-powered systems such as cataclysmic variables, X-ray binaries, and active galactic nuclei. For these sources, short wavelength spectral features are formed in the transfer of X-radiation from a powerful central source outward through a cooler, surrounding medium. The line emitting gas is photoionized and the level populations are determined largely by recombination cascades and photoexcitation as opposed to collisional effects. These processes can be rather complex and many uncertainties remain. We are developing a new approach to this problem using time-resolved studies of laser produced plasmas. Experiments which are currently underway include the measurements of: (a) inner and outer shell photoabsorption cross-sections of intermediate ions of abundant elements, and (b) fluorescent excitation processes due to wavelength coincidences of resonant transitions from different ions. In connection with this program, we have developed a novel reflection grating spectrometer coupled to a streak camera which provides high resolution spectra at soft X-ray and EUV wavelengths at the sub-nanosecond level. We describe our laboratory facility and some of our preliminary experimental results.
Monte Carlo Algorithms for Moments of Transition Arrays
Authors: Goldberg A. , Bloom S.D. 
Published: July 2016

AbstractClosed expressions for the first, second, and (in some cases) the third moment of atomic transition arrays now exist. Recently a method has been developed for getting to very high moments (up to the 12th and beyond) in cases where a “collective” state-vector (i.e. a state-vector containing the entire electric dipole strength) can be created from each eigenstate in the parent configuration. Both of these approaches give exact results. Herein we describe astatistical(or Monte Carlo) approach which requires onlyonerepresentative state-vector |RV&gt; for the entire parent manifold to get estimates of transition moments of high order. The representation is achieved through the random amplitudes associated with each basis vector making up |RV&gt;. This also gives rise to the dispersion characterizing the method, which has been applied to a system (in the M shell) with≈250,000 lines where we have calculated up to the 5th moment. It turns out that the dispersion in the moments decreases with the size of the manifold, making its application to very big systems statistically advantageous. A discussion of the method and these dispersion characteristics will be presented.
Wavelengths of the 3p-3d Transitions of the Co- and Fe-LIKE Ions: The Effects of Electron Correlation
Authors: Chen M.H. 
Published: July 2016

AbstractThe experimental observations of the 3p63d92D – 3p53d102P transitions of the Co-like ions and 3p63d83F4– 3p53d93F3of the Fe-like ions have recently been extended to highly charged ions of heavy elements up to uranium (Z = 92). A comparison between the observed energies and calculated values from the Dirac-Fock model indicated persistent discrepancies of 3–4 eV for all ions. Systematic multiconfiguration Dirac–Fock calculations for these transitions have been carried out with emphasis on the effects of electron correlation. The previously found discrepancies between theory and experiment have mostly been removed after the inclusion of the electron–electron correlation effects in the theoretical calculations.
Density and Temperature Diagnostics of a Ne-Like Germanium Plasma Created by Laser
Authors: Berthier E. , Bourgade J.L. , Combis P. , Jacquemot S. , Le Breton J.P. , Louis-Jacquet M. , Naccache D. , Nail M. , Peyrusse O. 
Published: July 2016

AbstractIn the frame-work of X-ray laser studies, experiments on Ne-like Ge plasma have been performed by laser Irradiation at λ = 1.053 μm. Amplification in lasing transitions has been observed by varying the plasma length. Theoretical calculations of excited level population allow us to determine density and temperature from line intensity ratios.
The Calculations for Determination of the Age of Supernova Remnants and Galaxy Clusters by Measurements of Hyperfine Splitting in Highly ionized Atoms with Unstable Nuclei
Authors: Band I.M. , Listengarten M.A. , Trzhaskovskaya M.B. 
Published: July 2016

The possibility of using the transitions between HFS components of atoms with nonstable nuclei in the spectra of hot gas in the supernova remnants and galaxy clusters for obtaining the information on the age of the objects was mentioned in /l/ without calculations. Here we present the numerical results for some ionized atoms obtained by relastivistic Hartree-Fock-Dirac method. Fermi distribution of nuclear charge density, vacuum polarisation, electron anomalous magnetic moment and reduced mass were taken into account. The HFS energy levels can be written aswhere A=A’(μ/J). HFS constants A’ in millielectronvolts for H- Li- and Na-like ions of unstable isotops with well known magnetic moments with Z &lt; 53 are given in the table (abundance rapidly decreases with increasing of Z). For the s-electrons, wavelength λ = (hcJ)/(Aμ(J+(1/2))); J is the nuclear spin, hc= 1,23985.10−4eV.cm T1/2is the halflife.
Recent Radiative and Collisional Atomic Data of Astrophysical Interest
Authors: Baluja K.L. , Butler K. , Le Bourlot J. , Zeippen C.J. 
Published: July 2016

SummaryUsing sophisticated computer programs and elaborate physical models, accurate radiative and collisional atomic data of astrophysical interest have been or are being calculated. The cases treated include radiative transitions between bound states in the 2p4and 2s2p5configurations of many ions in the oxygen isoelectronic sequence, the photoionisation of the ground state of neutral iron, the electron impact excitation of the fine-structure forbidden transitions within the 3p3ground configuration of CℓIII, Ar IV and K V, and the mass-production of radiative data for ions in the oxygen and fluorine isoelectronic sequences, as part of the international Opacity Project.
XUV Lasers - A Survey of Progress
Authors: Key M.H. 
Published: July 2016

AbstractThere has been an upsurge recently of both progress and interest in the development of XUV and X-ray lasers to such an extent that it is now possible to envisage the systematic development and application of a new family of powerful pulsed XUV lasers. The potential and actual characteristics of these lasers and the highlights of recent work will be reviewed.
The Possibilities of the Use of Replica X-Ray Imaging Mirrors in Plasma Diagnostics
Authors: Hudec R. , Valníček B. , Svátek L. , Landa V. , Fiedorowicz H. 
Published: July 2016

AbstractThe replica technology based on galvanoplastics offers the unique possibility of manufacturing of precise light-weight and low-cost imaging X-ray mirrors having both very small and large apertures of various types (paraboloid-hyperboloid, paraboloid-paraboloid, elipsoid- hyperboloid). Some of the further advantages such as the wide use of X-ray microscopic systems and the possibility to built large arrays of identical optical systems for simultaneous multispectral analysis are discussed together with the presentation of some examples of the manufactured mirrors. The first preliminary results are also presented.
Ultraviolet Absorption of Refractory Elements by a Dual Laser Plasma Method
Authors: Costello J.T. , Lynam W.G. , Carroll P.K. 
Published: July 2016

AbstractThe dual laser-produced plasma technique for the study of ionic absorption spectra has been developed by the use of two Q-switched ruby lasers to enable independent generation of the absorbing and back-lighting plasmas. Optical pulse handling is used in the coupling cicuits to enable reproducible pulse delays from 250 nsec. to 10 msec, to be achieved. At delay times &gt; 700 nsec. spectra of essentially pure neutral species are observed. The technique is valuable, not only for obtaining the neutral spectra of highly refractory and/or corrosive materials but also for studying behaviour of ionic species as a function of time. Typical spectra are shown in Fig. 1.
Recent Results on Soft X-Ray Amplification by Lithium-Like Ions in Plasmas
Authors: Carillon A. , Klisnick A. , Jamelot G. , Gauthé B. , Gadi F. , Jaeglé P. 
Published: July 2016

AbstractWe have shown that several transitions of Li-like ions give rise to population inversions during the recombination of laser-plasmas /1/. An extensive study has been made for the 3d–5f transition lying at 105.7 Å. It has shown a gain coefficient with a maximum around 2cm−1occuring about 6 nanosecond after the top of the 2-ns laser pulse. We extended recently this study to the 3d–4f line ar 154.7 Å and we observed a similar value of gain with the same temporal behaviour. Moreover, following calculated predictions for higher-Z ions /2/, we studied the 3d-5f transition of S13+which takes place at 65.2 Å. This study gives the first preliminary evidence of a gain coefficient of about 1 cm−1.
Some Applications in Atomic Physics of the Theory of Coupled Differential Equations
Authors: Chuan C.X. , Bougouffa S. 
Published: July 2016

La théorie sur la séparation d’un système d’équations différentielles couplées est appliquée à deux exemples comportant chacun deux équatlons. Nous présentons une discussion des résultats numériques ainsi qu’une généralisation à un systèms avec un nombre quelconque d’équations.The theory on the separation of a system of coupled differential equations is applied to two examples each having two equations. Numerical results are discussed and a generalisation to a system of any number of equations will be outlinedThe system of coupled differential equations (CDE) to be considered here is:The qeneral theory has already been presented In previous papers [1], [2],we continue to keep in the present one the same notations and conventions. Its implementation as well as the test of its efficiency will be discussed below.
High Resolution X-Ray Spectroscopy at Jet
Authors: Giannella R. 
Published: July 2016

AbstractA high resolution X-ray crystal spectrometer was installed at JET in 1986. The main task of this instrument, designed and built by the ENEA Frascati Laboratory in collaboration with JET, is the measurement of the ion temperature and rotation velocity from Doppler broadenings and shifts. Stringent operation requirements considerably conditioned its versatility as a survey instrument or a tool for fundamental research. The unique conditions of the JET plasmas, however, allowed to observe in high resolution and identify lines from the highest ionization stages (B-like to H-like) of nickel in the vicinity of the resonance transitions of the one- and two-electron systems of this element. These spectra and their relevance to the study of JET physics are briefly presented. The comparison with atomic physics theoretical computations of He-like and H-like ions spectra observed at JET is also shortly presented. The most intense among these lines could regularly be monitored with adequate time resolution as to allow the production of an extensive data base. The experimental spectra are simulated by integrating the theoretical ones along the spectrograph line of sight across the plasma. Ion temperature as well as rotation velocity measurements in ohmic plasmas and additionally heated ones are discussed and their relationship with other physical quantities and operational parameters are shortly reviewed. Details of the spectrometer design, its lay-out on the JET site and its operational capabilities are also given.
Localisation of Chromospheric Evaporation in Solar Flares, by the Analysis of X-Ray Spectra
Authors: Gabriel A.H. , Millier F. , Lizambert N. 
Published: July 2016

AbstractAnalysis of solar flares using the data from the Bent Crystal Spectrometer on the SMM solar flare satellite, shows a thermal plasma which expands vertically at a velocity of up to 350 km s−1. This plasma, at a temperature of the order 25 106K is observed in the line radiation of He-like Ca XIX. Its velocity is determined by measuring the blue shift of the resonance line “w”, whereas its intensity is expressed relatively to that of the stationary component. We analyse the variations of velocity and relative intensity of the evaporating plasma as a function of its location on the solar disc for 33 flares during the year 1980. The results are compared with the values expected from two alternative models A and B. On the basis that when observed at the limb, such flares do not usually show a blue shift, model A interprets this as due to the fact that the motion of the explosive plasma is perpendicular to the line-of-sight. Model B assumes that the process of chromospheric evaporation produces a “well” in the chromosphere, and therebye occults some of the emission of the ejected material. It is clear that the two models predict different velocity and relative intensity variations as a function of the distance of the flare from disc center. The lack of blue shift for 10 disc flares supports strongly the model B, i.e the existence of a “well” whose depth / diameter is between 0.1 and 5 as shown by our observations.
Needs for High Resolution Spectroscopy in Ultraviolet Solar Physics
Authors: Lemaire P. 
Published: July 2016

AbstractThe study of the solar atmosphere (from 5000 °K to few millions °K) is made through ultraviolet lines emitted by ionized elements. Some experiments (OSO 8, SMM, HRTS), observing above 100 nm have resolved the fine solar structure with a good spectral resolution. The understanding of the heating processes, the solar wind generation and its acceleration mechanisms require a global and detailed mass and energy budget of the atmosphere. The new ultraviolet spectrometers proposed on SOHO satellite are able to combine enough angular, spectral and temporal resolutions to establish this budget.
The ESO Off-line Telescope Testing Technique Illustrated with Results for the MPIA 2.2 m Telescope II
Authors: Wilson R.N. , Franza F. , Noethe L. , Tarenghi M. 
Published: July 2016

The ESO test device is based on the proposal of ShackFig. 1 shows the principle of this method, which we call the SHACKHARTMANN (S-H) method as it is derived from the well-known conventional Hartmann technique. The beam from the telescope focus (6) is transmitted by a beam-splitting cube (2) of high quality to a collimating (Fabry) doublet objective (3). This images the exit pupil of the telescope to the plane (4) where a special SHACK lenticular raster is inserted. Each lens of this raster then forms a point image of that part of the parallel beam incident upon it on to a photographic plate (5) placed at the focal distance of the raster lenses from (4). The angular aberration in the telescope image is thus transferred through the system and shows as a transverse displacement of the spots.
Astronomical Seeing at Mauna Kea and in Particular at the CFHT
Authors: Racine René 
Published: July 2016

AbstractThe astronomical seeing at the CFHT is excellent. It now averages <FWHM> = 0.9" and is continuously improving as a result of seeing conservation measures in the telescope building. Our studies suggest that the average natural seeing on Mauna Kea should be ~ 0.6". Very high (<0.2") resolution imaging at the CFHT, through adaptive optics, appears feasible.
On the Importance of Active Image Stabilisation
Authors: Noordam J.E. 
Published: July 2016

AbstractThe performance of an optical telescope can be improved considerably by opening the shutter only at moments of good seeing. The resulting instantaneous highresolution images must be corrected for shift before adding them all together. The optimum aperture diameter for which this technique works well is 1 meter or less, depending on atmospheric conditions. Image stabilisation not only improves the resolution and thus the point-source sensitivity, but it is also expected to improve the performance of speckle interferometry and optical aperture synthesis. This makes its implementation on large telescopes desirable. While it is certainly possible to do this by treating a large filled aperture like a set of independent subapertures, a much more logical approach would be to build an array of 1-meter telescopes, preferably mounted in a single large frame so that it can be pointed in all directions without extensive pathlength compensation. Such a “Many Mirror Telescope” has many advantages, and is feasible because image stabilisation helps to solve the beam-combining problem.
Refractive vs Reflective Correctors
Authors: Richardson E.H. , Morbey C.L. 
Published: July 2016

SummaryImproved designs of refractive correctors produce excellent images with fast telescopes such as those with an F/1.5 prime focus and F/3.5 secondary focus. The fields are flat and there is compensation for the chromatic effect caused by windows. Disadvantages of such correctors are that stray light is produced at the optical surfaces, the elements must be supported at their edges, prerequisite high quality glass is available in only limited sizes, and all wavelengths are not transmitted.Reflective correctors, on the other hand, can produce diffraction limited images at all wavelengths and the mirrors can be supported across their backs as well as at their edges. Disadvantages are that the images are degraded by any substantial window (such as a detector faceplate), there is more central obstruction, and the correctors are sometimes very large and heavy.Except, perhaps, for a specialized telescope, such as one devoted to multi-object slit spectroscopy using fibres, the refractive corrector is preferable at fast foci.A good combination is a Ritchey-Chretien (R-C) telescope with refractive correctors at the fast prime and secondary foci, and a reflective corrector-magnifier for the slow infrared focus.
Focal Reducer Techniques for Direct Imaging and Field Spectroscopy with Large Telescopes
Authors: Geyer Edward H. , Nelles Bruno 
Published: July 2016

AbstractTo exploit the full effectiveness of large ground based telescopes, the focal reducer technique can be applied very adequately. We review recent Hoher List observatory developments of observing techniques for direct imaging, field spectroscopy with multi-slit and masking methods for background supression and double-grism arrangements (heliometer principle)for absolute radial velocity determinations with a focal reducer field spectrograph.
Interstellar Matter with Very Large Telescopes
Authors: Lequeux J. 
Published: July 2016

Interstellar matter is certainly one of the fields where a very large telescope (VLT) will prove to be most fruitful. This includes (somewhat paradoxically, but this will be explained later) the study of extended emissions. I will now examine in turn the different domains of interest for a VLT.I. Neutral diffuse matterOptical and near IR observations will mainly contribute to this domain through high-resolution spectroscopy of interstellar absorption lines in the spectra of stars. These lines are resonant lines of atoms (NaI, KI, etc.) or ions (CaII, TiII, etc.) as well as of some molecules (CH+, CH, CN, CS+, C2 in the near IR). Clearly this kind of study is always photon - limited; a VLT will collect more photons than present telescopes, thus increase the possibilities considerably.
Options for a New Arizona Observatory: Configurations, Costs and Site
Authors: Woolf N.J. , Angel J.R.P. , Williams J.T. 
Published: July 2016

This paper is concerned with the process of creating a major observatory at minimum cost. Its premises are that cost optimization starts with an appropriately modestly priced building block, a 7.5m telescope. There are many possible configurations in which this building block can be used, ranging from a single telescope or a set of separate telescopes with at most electronic data addition, to an MMT in which the light of all telescopes can be phased when desired. In addition there are options for using elements in a non-redundant linear array or Michelson inteferometer. We provide the reader with a means of estimating costs of different facilities all on the same basis, and tied to the actual cost of producing the MMT.It is also important to place the observatory on a site which maximizes the output per unit cost of the facility. We discuss the selection process which has led to Mt. Graham in Arizona as being likely to satisfy this criterion. We give brief details of our preliminary knowledge about the site.
Baade-Wesselink Radii of Long Period Cepheids New Observational Results
Authors: Coulson Iain M. , Caldwell John A. R. , Gleren Wolfgang 
Published: July 2016

AbstractThe radii of Galactic Cepheids as determined from a version of the Baade-Wesselink technique are shown to depend upon the colour index used to define the temperature scale. The (V-l) radii are systematically larger than the commonly used (B-V) radii and are probably better estimators of the true radii. There still remains a problem, however, in reconciling the period-radius relation with the period-luminosity-colour relation.
On the Brightness and Pulsational Properties of Yellow Supergiants
Authors: Arellano Ferro A. 
Published: July 2016

AbstractMost of the existing data in the literature is used to search for the periodicity of five yellow supergiant variables. The pulsational mode and Q-values are discussed, being the luminosity the key parameter for their accurate determination. An attempt to find the spherical harmonic l from the light and colour variation phase shift is carried out.
Theory of Cepheid Pulsation: Excitation Mechanisms
Authors: Cox John P. 
Published: July 2016

AbstractThe various excitation mechanisms (eight in all) that have been proposed to account for the vibrational instability of variable stars, are surveyed. The most widely applied one is perhaps the “envelope ionization mechanism.” This can account for most of the essential characteristics of the “instability strip.” A simple explanation of the period-luminosity relation of classical Cepheids is given. A few outstanding problems in pulsation theory are also listed.
New Distances to the Magellanic Clouds
Authors: Visvanathan N. 
Published: July 2016

AbstractThe mean phase magnitudes at the IV waveband (1.05 micron) of thirteen Cepheids in the SMC and the LMC and nine Cepheids in groups and clusters in the Galaxy, are used in conjunction with periods, to construct P–L(IV) relations in these galaxies. The slopes and the dispersions of the relations are nearly the same. We derive a distance modulus of 19.11±0.07 for the SMC and 18.82±0.07 for the LMC.
The Distances to Nearby Galaxies from Near-Infrared Photometry of Cepheids
Authors: McAlary Christopher W. , Welch Douglas L. 
Published: July 2016

AbstractNear-infrared photometry of Cepheid variables in the Local Group galaxies, NGC 6822, IC 1613, and M33, and in the M81 Group galaxy, NGC 2403 has been used to determine new, independent distances to these objects, which are almost unaffected by dust extinction and by differences in metallicities among the galaxies.