Distribution by Scientific Domains
Distribution within Physics and Astronomy

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  • Selected Abstracts

    Optimizing the point spread function in phase-encoded magnetic resonance microscopy

    A.G. Webb
    Abstract Three-dimensional phase-encoded magnetic resonance microscopy is the most promising method for obtaining images with isotropic spatial resolutions on the order of a few micrometers. The attainable spatial resolution is limited by the available gradient strength (Gmax) and the molecular self-diffusion coefficient (D) of the sample. In this study, numerical simulations in the microscopic-size regime are presented in order to show that for given values of Gmax and D, there exists an optimum number of phase-encoding steps that maximize the spatial resolution in terms of minimizing the full-width at half-maximum (FWHM) of the image point spread function (PSF). Unlike the case of "macroscopic" imaging, in which diffusion plays an insignificant role in determining spatial resolution, acquiring data beyond this optimal value actually degrades the image PSF. An alternative version of phase encoding, using a variable phase-encoding time rather than a variable gradient strength, is analyzed in terms of improvements in the image PSF and/or reductions in the data acquisition time for a given spatial resolution. 2004 Wiley Periodicals, Inc. Concepts Magn Reson 22A: 25,36, 2004. [source]

    Effect of AlN doping on the growth morphology of SiC

    N. B. Singh
    Abstract AlN doped SiC films were deposited on on-axis Si-face 4H-SiC (0001) substrates by the physical vapor transport (PVT) method. Thick film in the range of 20 ,m range was grown and morphology was characterized. Films were grown by physical vapor deposition (PVD) in a vertical geometry in the nitrogen atmosphere. We observed that nucleation occurred in the form of discs and growth occurred in hexagonal geometry. The X-ray studies showed (001) orientation and full width of half maxima (FWHM) was less than 0.1 indicating good crystallinity. We also observed that film deposited on the carbon crucible had long needles with anisotropic growth very similar to that of pure AlN. Some of the needles grew up to sizes of 200 ,m in length and 40 to 50 ,m in width. It is clear that annealing of SiC-AlN powder or high temperature physical vapor deposition produces similar crystal structure for producing AlN-SiC solid solution. SEM studies indicated that facetted hexagons grew on the top of each other and coarsened and merged to form cm size grains on the substrate. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Growth, etching morphology and spectra of LiAlO2 crystal

    Taohua Huang
    Abstract ,-LiAlO2 single crystal was successfully grown by Czochralski method. The crystal quality was characterized by X-ray rocking curve and chemical etching. The effects of air-annealing and vapor transport equilibration (VTE) on the crystal quality, etch pits and absorption spectra of LiAlO2 were also investigated in detail. The results show that the as-grown crystal has very high quality with the full width at half maximum (FWHM) of 17.7-22.6 arcsec. Dislocation density in the middle part of the crystal is as low as about 3.0103 cm,2. The VTE-treated slice has larger FWHM value, etch pits density and absorption coefficient as compared with those of untreated and air-annealed slices, which indicates that the crystal quality became inferior after VTE treatment. ( 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Growth and characterization of magneto-optical YFeO3 crystals

    Hui Shen
    Abstract The floating zone growth of magneto-optical crystal YFeO3 has been investigated. The polycrystalline feed rod was prepared by a pressure of 250MPa and sintering at about 1500C. A crack- free YFeO3 single crystal has been successfully grown. The crystal preferred to crystallize along <100> direction with about 10 deviation. The X-ray rocking curve of the crystal has a FWHM of 24 arcsec, confirming the high crystal quality of the sample. The (100) plane was etched by hot phosphoric acid and the dislocation density was about 104/cm2. A thin outer layer with Y2O3 -rich composition was found at the periphery of as-grown crystals, which was attributed to the Fe2O3 evaporation during growth. ( 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

    Atomic Layer Deposition of UV-Absorbing ZnO Films on SiO2 and TiO2 Nanoparticles Using a Fluidized Bed Reactor,

    David M. King
    Atomic layer deposition (ALD) was used to apply conformal, nanothick ZnO coatings on particle substrates using a fluidized bed reactor. Diethylzinc (DEZ) and water were used as precursors at 177,C. Observed growth rates were ca. 2.0 /cycle on primary particles as verified by HRTEM. ICP-AES and XPS were used to quantify Zn:substrate ratios. Layers of 6, 18, and 30 nm were deposited on 550 nm SiO2 spheres for UV blocking cosmetics particles. TiO2 nanoparticles were coated in the second part of this work by ZnO shells of 2, 5, and 10 nm thickness as novel inorganic sunscreen particles. The specific surface area of powders changed appropriately after nanothick film deposition using optimized conditions, signifying that high SA particles can be functionalized without agglomeration. The ZnO layers were polycrystalline as deposited and narrowing of the FWHM occurred upon annealing. Annealing the ZnO-TiO2 nanocomposite powder to 600,C caused the formation of zinc titanate (Zn2TiO4) in both oxygen-rich and oxygen-deficient environments. The non-ideal surface behavior of the DEZ precursor became problematic for the much longer times required for high surface area nanoparticle processing and results in Zn-rich films at this growth temperature. In situ mass spectrometry provides process control capability to functionalize bulk quantities of nano- and ultrafine particles without significant precursor waste or process overruns. ZnO overlayers can be efficiently deposited on the surfaces of primary particles using ALD processing in a scalable fluidized bed reactor. [source]

    A New Sol,Gel Material Doped with an Erbium Complex and Its Potential Optical-Amplification Application,

    L.-N. Sun
    Abstract The crystal structure of a ternary Er(DBM)3phen complex (DBM,=,dibenzoylmethane; phen,=,1,10-phenanthroline) and its in-situ synthesis via a sol,gel process are reported. The infrared (IR), diffuse reflectance (DR), and fluorescence spectra of the pure complex and the Er3+/DBM/phen co-doped luminescent hybrid gel, formed via an in-situ method (ErDP gel), have been investigated. The results reveal that the erbium complex is successfully synthesized in situ in the ErDP gel. Excitation at the maximum absorption wavelength of the ligands resulted in the typical near-IR luminescence (centered at around 1.54,,m) resulting from the 4I13/2,,,4I15/2 transition of the Er3+ ion, which contributes to the efficient energy transfer from the ligands to the Er3+ ion in both the Er(DBM)3phen complex and the ErDP gel (an antenna effect). The full width at half maximum (FWHM) centered at 1541,nm in the emission spectrum of the ErDP gel is 72,nm, which has potential for optical-amplification applications. Further theoretical analysis on the Er3+ ion in the ErDP gel shows that it appears to be a promising candidate for tunable lasers and planar optical amplifiers. [source]

    Quantized Double-Layer Charging of Rhodium2057(Tridecylamine)321 Clusters Using Differential Pulse and Cyclic Voltammetry,

    ADVANCED MATERIALS, Issue 2 2007
    A. Kakade
    Rhodium nanoclusters show a series of quantized double-layer-charging events in solution-phase voltammetry at room temperature (see figure). The unusual variation in the FWHM for both the cathodic and anodic regions in differential pulse voltammetry experiments can be explained by several complex factors including reorganization and disproportionation of charged clusters coupled with electron-transfer processes pertaining to the Rh,Rh bonds. [source]

    Enhancement of crystalline perfection by organic dopants in ZTS, ADP and KHP crystals as investigated by high-resolution XRD and SEM

    S. Parthiban
    To reveal the influence of complexing agents on crystalline perfection, tristhiourea zinc(II) sulfate (ZTS), ammonium dihydrogen phosphate (ADP) and potassium hydrogen phthalate (KHP) crystals grown by slow-evaporation solution growth technique using low concentrations (5 10,3M) of dopants like ethylenediamminetetraacetic acid (EDTA) and 1,10-phenanthroline (phen) were characterized by high-resolution X-ray diffractometry (XRD) and scanning electron microscopy (SEM). High-resolution diffraction curves (DCs) recorded for ZTS and ADP crystals doped with EDTA show that the specimen contains an epilayer, as observed by the additional peak in the DC, whereas undoped specimens do not have such additional peaks. On etching the surface layer, the additional peak due to the epilayer disappears and a very sharp DC is obtained, with full width at half-maximum (FWHM) of less than 10,arcsec, as expected from the plane wave dynamical theory of X-ray diffraction for an ideally perfect crystal. SEM micrographs also confirm the existence of an epilayer in doped specimens. The ZTS specimen has a layer with a rough surface morphology, having randomly oriented needles, whereas the ADP specimen contains a layer with dendric structure. In contrast to ADP and ZTS crystals, the DC of phen-doped KHP shows no additional peak, but it is quite broad (FWHM = 28,arcsec) with a high value of integrated intensity, , (area under the DC). The broadness of the DC and the high value of , indicate the formation of a mosaic layer on the surface of the crystal. However, similar to ADP and ZTS, the DC recorded after etching the surface layer of the KHP specimen shows a very sharp peak with an FWHM of 8 arcsec. An SEM photograph of phen-doped KHP shows deep cracks on the surface, confirming the mosaicity. After removing the surface layer, the SEM pictures reveal a smooth surface. A similar trend is observed with other complexing agents, like oxalic acid, bipy and picolinic acid. However, only typical examples are described in the present article where the effects were observed prominently. The investigations on ZTS, ADP and KHP crystals, employing high-resolution XRD and SEM studies, revealed that some organic dopants added to the solution during the growth lead to the formation of a surface layer, due to complexation of these dopants with the trace metal ion impurities present in the solution, which prevents the entry of impurities, including the solvent, into the crystal, thereby assisting crystal growth with high crystalline perfection. The influence of organic dopants on the second harmonic generation efficiency is also investigated. [source]

    Limitations of asymmetric parallel-beam geometry

    N. A. Raftery
    Bragg diffraction peak profiles and intensities in asymmetric (,,2,) diffraction using a mirror-based parallel-beam geometry were compared with symmetric parallel-beam (,,2,) and conventional Bragg,Brentano (,,2,) diffraction for a powdered quartz sample and the NIST standard reference material (SRM) 660a (LaB6, lanthanum hexaboride). A comparison of the intensities and line widths (full width at half-maximum, FWHM) of these techniques demonstrated that low incident angles (,,<,5) are preferable for the parallel-beam setup. For higher , values, if 2,,<,2,, mass absorption reduces the intensities significantly compared with the Bragg,Brentano setup. The diffraction peak shapes for the mirror geometry are more asymmetric and have larger FWHM values than corresponding peaks recorded with a Bragg,Brentano geometry. An asymmetric mirror-based parallel-beam geometry offers some advantages in respect of intensity when compared with symmetric geometries, and hence may be well suited to quantitative studies, such as those involving Rietveld analysis. A trial Rietveld refinement of a 50% quartz,50% corundum mixture was performed and produced adequate results. [source]

    Two stage growth of microdiamond in UHP dolomite marble from Kokchetav Massif, Kazakhstan

    H. Ishida
    Abstract The abundance and morphology of microdiamond in dolomite marble from Kumdy-kol in the Kokchetav Massif, are unusual; a previous study estimated the maximum content of diamonds in dolomite marble to be about 2700 carat ton,1. Microdiamond is included primarily in garnet, and occasionally in diopside and phlogopite pseudomorphs after garnet. They are classified into three types on the basis of their morphology: (1) S-type: star-shaped diamond consisting of translucent cores and transparent subhedral to euhedral very fine-grained outer parts; (2) R-type: translucent crystals with rugged surfaces; and (3) T-type: transparent, very fine-grained crystals. The S-type is the most abundant. Micro-Laue diffraction using a 1.6-m X-ray beam-size demonstrated that the cores of the star-shaped microdiamond represent single crystals. In contrast, the most fine-grained outer parts usually have different orientations compared to the core. Laser,Raman studies indicate that the FWHM (Full Width at Half Maximum) of the Raman band of the core of the S-type diamond is slightly larger than that for the outer parts. Differences in morphology, crystal orientations, and in the FWHM of the Raman band between the core and the fine-grained outer-parts of S-type microdiamond suggest that the star-shaped microdiamond was formed discontinuously in two distinct stages. [source]

    Raman spectroscopy of synthetic, geological and biological vaterite: a Raman spectroscopic study

    U. Wehrmeister
    Abstract Raman spectroscopy was used to study vaterite samples of biological, geological and synthetic origin. The Raman band positions and the full width at half-maximum (FWHM) of the lattice modes and the internal modes of the carbonate ion of all specimens show no significant differences between vaterites of different origin. With increasing Mg concentrations, synthetic vaterite samples show increasing FWHM in the region of the lattice modes and the three ,1 bands, whereas no change in luminescence was detected. In contrast, in situ measurements of vaterite areas in freshwater cultured pearls (FWCPs) by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) together with the Raman spectra obtained at the same points show that the luminescence intensity in biological samples is affected by the magnesium content. The Raman spectroscopic features of vaterite and parisite-(Ce) are compared, and their similarities suggest that the structure of vaterite contains at least three crystallographically independent carbonate groups and similar carbonate group layers. A band at 263 cm,1 is observed for the first time in this study, whereas it could be demonstrated that bands previously reported at 130 and 190 cm,1 do not belong to vaterite. Copyright 2009 John Wiley & Sons, Ltd. [source]

    Changes in spectral features with varying mole fractions of anisaldehyde in binary mixtures

    A. Anis Fathima
    Abstract Raman and IR spectra of neat anisaldehyde (4-methoxybenzaldehyde (4MeOBz)) and its binary mixtures (in polar and nonpolar solvents) with varying mole fraction of 4MeOBz were investigated. The concentration dependence of the wavenumber position and line width (full width at half maximum, FWHM) was analyzed to study the interaction of the solute vibrational modes with the microscopic solvent environment. The wavenumbers of Raman modes of 4MeOBz, namely, the carbonyl stretching, aldehydic , (CH) and ring-breathing modes, showed a linear variation in the peak position for varying concentrations of 4MeOBz in the different solvents. The dependence of Raman line width with concentration of 4MeOBz of these modes was also taken into account. The solute,solvent interaction is stronger in 2-propanol and acetonitrile because of the formation of hydrogen bonds between them, whereas in benzene the interaction is too weak to affect the Raman modes. The modes, , (CO) in 2-propanol and aldehydic , (CH) in acetonitrile, gave a Gaussian-type line width variation, which was explained by the concentration fluctuation model, and the linear variation of the line widths was also interpreted by solute,solvent interactions. IR spectra were taken for these binary mixtures, which also give further support to these data. Copyright 2006 John Wiley & Sons, Ltd. [source]

    Polycapillary-optics-based micro-XANES and micro-EXAFS at a third-generation bending-magnet beamline

    Geert Silversmit
    A focusing system based on a polycapillary half-lens optic has been successfully tested for transmission and fluorescence -X-ray absorption spectroscopy at a third-generation bending-magnet beamline equipped with a non-fixed-exit Si(111) monochromator. The vertical positional variations of the X-ray beam owing to the use of a non-fixed-exit monochromator were shown to pose only a limited problem by using the polycapillary optic. The expected height variation for an EXAFS scan around the Fe K -edge is approximately 200,m on the lens input side and this was reduced to ,1,m for the focused beam. Beam sizes (FWHM) of 12,16,m, transmission efficiencies of 25,45% and intensity gain factors, compared with the non-focused beam, of about 2000 were obtained in the 7,14,keV energy range for an incoming beam of 0.5 2,mm (vertical horizontal). As a practical application, an As K -edge -XANES study of cucumber root and hypocotyl was performed to determine the As oxidation state in the different plant parts and to identify a possible metabolic conversion by the plant. [source]

    Crystal growth, optical properties, and continuous-wave laser operation of Nd3+ -doped CaNb2O6 crystal

    LASER PHYSICS LETTERS, Issue 10 2009
    Y. Cheng
    Abstract Laser crystal Nd:CaNb2O6 with excellent quality has been grown by Czochralski technique. The effective segregation coefficient of Nd3+ was studied by X-ray fluorescence method. The polarized absorption spectra and the fluorescence spectra of Nd:CaNb2O6 were measured at room temperature. The peak absorption cross section was calculated to be 6.20210,20 cm2with a broad FWHM of 7 nm at 808 nm for E , a light polarization. The emission cross section at 1062 nm is 9.87 10,20 cm2. We report what we believe to be the first demonstration of the continuous-wave Nd:CaNb2O6 laser operation under diode pumping. Output power of 1.86 W at 1062 nm was obtained with a slope efficiency of 19% in the CW regime. ( 2009 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

    Two-photon Raman-type self-induced transparency forfew-cycle laser pulses

    I. P. Prokopovich
    Abstract We show the both amplitude and spectrum dynamics of few-cycle laser pulses in two-photon Raman-type self-induced transparency in Ar+ ions, that permit to generate half-cycle laser pulses (FWHM) with more high amplitudes and photon energy as well as spectral widths. ( 2005 by Astro, Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source]

    Synthesis of CdSe quantum dots with luminescence in the violet region of the solar spectrum

    Nisha Shukla
    Abstract We have designed a simple, one-step synthesis of CdSe quantum dots with photoluminescence frequencies ranging from the red through to the violet region of the solar spectrum. The photoluminescence peaks have FWHM of 30 nm indicating absorption over a narrow range of wavelengths. The effect of solvent type and solvent boiling point on the physical and photoluminescence properties of the quantum dots has been studied. High boiling point, non-polar solvents shift the photoluminescence peak to longer wavelengths and low boiling point, polar solvents shift the photoluminescence peak to shorter wavelengths. Copyright 2009 John Wiley & Sons, Ltd. [source]

    In vivo behaviour of long-circulating liposomes in blood vessels in hamster inflammation and septic shock models,use of intravital fluorescence microscopy

    Jean-Marie Devoisselle
    Abstract This study aimed to observe liposome uptake by leukocytes in vivo. The study was performed on skin by using a dorsal skin-fold chamber implanted in golden hamsters using intravital microscopy. 5 and 6-CF-encapsulated polyethylene glycolated liposomes were injected intravenously. The skin microcirculation was observed with an intravital Eclipse E800 Nikon microscope (using 40, 80 magnification) fitted with a Xenon light source and an epifluorescence assembly (excitation, 470,nm, FWHM 40,nm; emission, 540,nm, FWHM 40,nm). An ultra-high sensitivity videocamera mounted on the microscope projected the image onto a monitor, and the images (720,,576 pixels) were recorded for playback analysis with a digital video cassette recorder. An acute inflammatory response was obtained by removing one complete layer of skin and the underlying fascia and avascular tissue on the opposing side of the flap corresponding to an area equivalent to the window aperture. Using this model and set-up, leukocyte rolling and adhesion were easily observed and the entry of PEGylated liposomes into hamster blood leukocytes was studied for a period of 6,h. PEGylated liposomes were clearly identified alone inside the blood flow and inside the leukocytes as soon as the inflammatory reaction appeared. This study shows for the first time that blood leukocytes in their natural milieu of whole blood are capable of interacting with, and taking up, liposomes. This observation is in accordance with previous in vitro studies. Copyright 2001 John Wiley & Sons, Ltd. [source]

    Quantitative lung perfusion mapping at 0.2 T using FAIR True-FISP MRI

    Petros Martirosian
    Abstract Perfusion measurements in lung tissue using arterial spin labeling (ASL) techniques are hampered by strong microscopic field gradients induced by susceptibility differences between the alveolar air and the lung parenchyma. A true fast imaging with steady precession (True-FISP) sequence was adapted for applications in flow-sensitive alternating inversion recovery (FAIR) lung perfusion imaging at 0.2 Tesla and 1.5 Tesla. Conditions of microscopic static field distribution were assessed in four healthy volunteers at both field strengths using multiecho gradient-echo sequences. The full width at half maximum (FWHM) values of the frequency distribution for 180,277 Hz at 1.5 Tesla were more than threefold higher compared to 39,109 Hz at 0.2 Tesla. The influence of microscopic field inhomogeneities on the True-FISP signal yield was simulated numerically. Conditions allowed for the development of a FAIR True-FISP sequence for lung perfusion measurement at 0.2 Tesla, whereas at 1.5 Tesla microscopic field inhomogeneities appeared too distinct. Perfusion measurements of lung tissue were performed on eight healthy volunteers and two patients at 0.2 Tesla using the optimized FAIR True-FISP sequence. The average perfusion rates in peripheral lung regions in transverse, sagittal, and coronal slices of the left/right lung were 418/400, 398/416, and 370/368 ml/100 g/min, respectively. This work suggests that FAIR True-FISP sequences can be considered appropriate for noninvasive lung perfusion examinations at low field strength. Magn Reson Med, 2006. 2006 Wiley-Liss, Inc. [source]

    In situ micro-Raman and X-ray diffraction study of diamonds and petrology of the new ureilite UAE 001 from the United Arab Emirates

    Dominik C. HEZEL
    This is the first report of a meteorite in this country. The sample is heavily altered, of medium shock level, and has a total weight of 155 g. Bulk rock, olivine (Fo79.8,81.8) and pyroxene (En73.9,75.2, Fs15.5,16.9, Wo8.8,9.5) compositions are typical of ureilites. Olivine rims are reduced with Fo increasing up to Fo96.1,96.8. Metal in these rims is completely altered to Fehydroxide during terrestrial weathering. We studied diamond and graphite using micro-Raman and in situ synchrotron X-ray diffraction. The main diamond Raman band (LO = TO mode at ,1332 cm,1) is broadened when compared to well-ordered diamond single crystals. Full widths at half maximum (FWHM) values scatter around 7 cm,1. These values resemble FWHM values obtained from chemical vapor deposition (CVD) diamond. In situ XRD measurements show that diamonds have large grain sizes, up to >5 ,m. Some of the graphite measured is compressed graphite. We explore the possibilities of CVD versus impact shock origin of diamonds and conclude that a shock origin is much more plausible. The broadening of the Raman bands might be explained by prolonged shock pressure resulting in a transitional Raman signal between experimentally shock-produced and natural diamonds. [source]

    Experimental investigation into femtosecond fiber ring laser with passive mode locking

    Xiaoping Xie
    Abstract A passively mode-locked Er3+ -doped fiber ring laser is experimentally investigated, with the emphasis on its practical design by considering the effects of ring cavity length, pumping light power, and optical amplification on the femtosecond optical pulses obtained. It is shown that the designed fiber ring laser can operate at the center wavelength of 1550 nm to produce a train of periodic optical pulses with full width at half maximum (FWHM) of 270 fs, repetition frequency of 20 MHz, and average output optical power of 146 ,W. The resulting femtosecond optical pulses are then amplified by using three kinds of Er3+ -doped optical fibers with different lengths and Er3+ -doped concentrations, respectively, while employing the same pumping laser. In the experiments, both the FWHM of amplified optical pulses and the amplifier gain are measured under different conditions. The optimization of optical pulse width is also carried out in terms of pumping light power. 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 63,67, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23985 [source]

    Enhanced star formation in narrow-line Seyfert 1 active galactic nuclei revealed by Spitzer

    E. Sani
    ABSTRACT We present new low-resolution Spitzer mid-infrared spectroscopy of a sample of 20 ROSAT -selected local narrow-line Seyfert 1 galaxies (NLS1s). We detect strong active galactic nucleus (AGN) continuum in all and clear polycyclic aromatic hydrocarbon (PAH) emission in 70 per cent of the sources. The 6.2 ,m PAH luminosity spans three orders of magnitude, from ,1039 to ,1042 erg s,1, providing strong evidence for intense ongoing star formation in the circumnuclear regions of these sources. Using the Infrared Spectrograph/Spitzer archive, we gathered a large number of additional NLS1s and their broad-line counterparts (BLS1s) and constructed NLS1 and BLS1 subsamples to compare them in various ways. The comparison shows a clear separation according to full width at half-maximum (H,) [FWHM(H,)] such that objects with narrower broad H, lines are the strongest PAH emitters. We test this division in various ways trying to remove biases due to luminosity and aperture size. Specifically, we find that star formation activity around NLS1 AGN is larger than around BLS1 of the same AGN luminosity. The above result seems to hold over the entire range of distance and luminosity. Moreover, the star formation rate is higher in low black hole mass and high L/LEdd systems indicating that black hole growth and star formation are occurring simultaneously. [source]

    Spectral models for solar-scaled and ,-enhanced stellar populations

    P. Coelho
    ABSTRACT We present the first models allowing one to explore in a consistent way the influence of changes in the ,-element-to-iron abundance ratio on the high-resolution spectral properties of evolving stellar populations. The models cover the wavelength range from 3000 to 1.34 ,m at a constant resolution of full width at half-maximum (FWHM) = 1 and a sampling of 0.2 , for overall metallicities in the range 0.005 ,Z, 0.048 and for stellar population ages between 3 and 14 Gyr. These models are based on a recent library of synthetic stellar spectra and a new library of stellar evolutionary tracks, both computed for three different iron abundances ([Fe/H]=,0.5, 0.0 and 0.2) and two different ,-element-to-iron abundance ratios ([,/Fe]= 0.0 and 0.4). We expect our fully synthetic models to be primarily useful for evaluating the differential effect of changes in the ,/Fe ratio on spectral properties such as broad-band colours and narrow spectral features. In addition, we assess the accuracy of absolute model predictions in two ways: first, by comparing the predictions of models for scaled-solar metal abundances ([,/Fe]= 0.0) to those of existing models based on libraries of observed stellar spectra; and secondly, by comparing the predictions of models for ,-enhanced metal abundances ([,/Fe]= 0.4) to observed spectra of massive early-type galaxies in the Sloan Digital Sky Survey Data Release 4. We find that our models predict accurate strengths for those spectral indices that are strongly sensitive to the abundances of Fe and , elements. The predictions are less reliable for the strengths of other spectral features, such as those dominated by the abundances of C and N, as expected from the fact that the models do not yet allow one to explore the influence of these elements in an independent way. We conclude that our models are a powerful tool for extracting new information about the chemical properties of galaxies for which high-quality spectra have been gathered by modern surveys. [source]

    VIMOS-VLT spectroscopy of the giant Ly, nebulae associated with three z, 2.5 radio galaxies,

    M. Villar-Martn
    ABSTRACT The morphological and spectroscopic properties of the giant (>60 kpc) Ly, nebulae associated with three radio galaxies at z, 2.5 (MRC 1558,003, 2025,218 and 0140,257) have been investigated using integral field spectroscopic data obtained with the Visible Multi-Object Spectrograph (VIMOS) on VLT. The morphologies are varied. The nebula of one source has a centrally peaked, rounded appearance. In the other two objects, it consists of two spatial components. The three nebulae are aligned with the radio axis within ,30. The total Ly, luminosities are in the range (0.3,3.4) 1044 erg s,1. The Ly, spectral profile shows strong variation through the nebulae, with full width at half-maximum (FWHM) values in the range ,400,1500 km s,1 and velocity shifts Voffset, 120,600 km s,1. We present an infall model that can successfully explain the morphology, size, surface brightness distribution and the velocity field of the Ly, nebula associated with MRC 1558,003. It can also explain why Ly, is redshifted relative to other emission lines and the FWHM values of the non-resonant He ii line. This adds further support to our previous conclusion that the quiescent giant nebulae associated with this and other high-redshift powerful radio galaxies are in infall. A problem for this model is the difficulty to reproduce the large Ly, FWHM values, which might be the consequence of a different mechanism. We have discovered a giant (,85 kpc) Ly, nebula associated with the radio galaxy MRC 0140,257 at z= 2.64. It shows strikingly relaxed kinematics (FWHM < 300 km s,1 and Voffset, 120 km s,1), unique among high- z (,2) radio galaxies. [source]

    Atomic hydrogen in asymptotic giant branch circumstellar environments.

    A case study: X Her
    ABSTRACT We report the detection of the H i line at 21 cm from the circumstellar shell around the asymptotic giant branch star X Her using the position-switching technique with the Nanay Radio Telescope. At the star position, the line shows two components: (i) a broad one [full width at half-maximum (FWHM) , 13 km s,1] centred at ,72.2 km s,1 and (ii) a narrow one (FWHM , 4 km s,1) centred at ,,70.6 km s ,1. Our map shows that the source associated to the broad component is asymmetric with material flowing preferentially towards the north-east. This source extends to ,10 arcmin (,0.4 pc) from the star in that direction. On the other hand, the narrow component is detected only at the star position and indicates material flowing away from the observer. The total mass of atomic hydrogen is ,6.5 10,3 M, which, within a factor of 2, agrees with the estimate obtained from IRAS data at 60 ,m. [source]

    What controls the C iv line profile in active galactic nuclei?

    Alexei Baskin
    ABSTRACT The high-ionization lines in active galactic nuclei (AGN), such as C iv, tend to be blueshifted with respect to the lower-ionization lines, such as H,, and often show a strong blue excess asymmetry not seen in the low-ionization lines. There is accumulating evidence that the H, profile is dominated by gravity, and thus provides a useful estimate of the black hole mass in AGN. The shift and asymmetry commonly seen in C iv suggest that non-gravitational effects, such as obscuration and radiation pressure, may affect the line profile. We explore the relation between the H, and C iv profiles using the ultraviolet (UV) spectra available for 81 of the 87 z, 0.5 PG quasars in the Boroson & Green sample. We find the following. (1) Narrow C iv lines (full width at half-maximum, FWHM < 2000 km s,1) are rare (,2 per cent occurrence rate) compared with narrow H, lines (,20 per cent). (2) In most objects where the H, FWHM < 4000 km s,1 the C iv line is broader than H,, but the reverse is true when the H, FWHM > 4000 km s,1. This argues against the view that C iv generally originates closer to the centre, compared with H,. (3) C iv appears to provide a significantly less accurate, and possibly biased estimate of the black hole mass in AGN, compared with H,. (4) All objects where C iv is strongly blueshifted and asymmetric have a high L/LEdd, but the reverse is not true. This suggests that a high L/LEdd is a necessary but not sufficient condition for generating a blueshifted asymmetric C iv emission. (5) We also find indications for dust reddening and scattering in ,normal' AGN. In particular, PG quasars with a redder optical,UV continuum slope show weaker C iv emission, stronger C iv absorption and a higher optical continuum polarization. [source]

    An XMM,Newton observation of Ark 120: the X-ray spectrum of a ,bare' Seyfert 1 nucleus

    S. Vaughan
    ABSTRACT We report on a long (100 ks) XMM,Newton observation of the bright Seyfert 1 galaxy Arakelian 120. The source previously showed no signs of intrinsic reddening in its infrared,ultraviolet continuum and previous observations had shown no evidence for ionized absorption in either the ultraviolet or X-ray bands. The new XMM,Newton Reflection Grating Spectrometer data place tight limits on the presence of an ionized X-ray absorber and confirm that the X-ray spectrum of Ark 120 is essentially unmodified by intervening matter. Thus Ark 120 can be considered a ,bare' Seyfert 1 nucleus. This observation therefore offers a clean view of the X-ray spectrum of a ,normal' Seyfert galaxy free from absorption effects. The spectrum shows a Doppler broadened iron emission line (FWHM , 3 104 km s,1) and a smooth, continuous soft excess which appears to peak at an energy ,0.5 keV. This adds weight to the claim that genuine soft excesses (i.e. those due to a real steepening of the underlying continuum below ,2 keV) are ubiquitous in Seyfert 1 spectra. However, the detailed shape of the excess could not be reproduced by any of the simple models tested (power laws, blackbodies, Comptonized blackbodies, accretion disc reflection). This observation therefore demonstrates both the need to understand the soft excess (as a significant contributor to the luminosity of most Seyfert 1s) and the inability of the existing, simple models to explain it. [source]

    Evolution of the 3.3-,m emission feature in the Red Rectangle

    In-Ok Song
    ABSTRACT Medium-resolution infrared spectroscopic observations of the biconical Red Rectangle nebula in the region of the 3.3-,m unidentified infrared (UIR) emission band are reported. The data were recorded at UKIRT using CGS4 and have allowed the peak wavelength, width, profile and intensity of the 3.3-,m feature to be investigated as a function of offset from the central star HD 44179. Analysis of the profile of the feature along the north-western bicone interface shows an evolution from Type 2 to Type 1 in the classification of Tokunaga et al. The 3.3-,m band recorded on-star shows a close fit to a Lorentzian profile, possibly suggesting a single class of carriers. Subtraction of the Lorentzian fit to the on-star spectrum from the spectrum at each offset reveals a new ,3.28'-,m emission feature that grows in intensity relative to the main 3.3-,m band as a function of distance from the central star. The 3.28-,m emission band at large offset appears to correspond well in wavelength and FWHM with an absorption feature seen towards the Galactic Centre. [source]

    Measuring the black hole masses of high-redshift quasars

    R. J. McLure
    Abstract A new technique is presented for determining the black hole masses of high-redshift quasars from optical spectroscopy. The new method utilizes the full-width at half-maximum (FWHM) of the low-ionization Mg ii emission line and the correlation between the broad-line region (BLR) radius and the continuum luminosity at 3000 . Using archival ultraviolet (UV) spectra it is found that the correlation between BLR radius and 3000- luminosity is tighter than the established correlation with 5100- luminosity. Furthermore, it is found that the correlation between BLR radius and 3000- continuum luminosity is consistent with a relation of the form RBLR,,L1/2,, as expected for a constant ionization parameter. Using a sample of objects with broad-line radii determined from reverberation mapping it is shown that the FWHM of Mg ii and H, are consistent with following an exact one-to-one relation, as expected if both H, and Mg ii are emitted at the same radius from the central ionizing source. The resulting virial black hole mass estimator based on rest-frame UV observables is shown to reproduce black hole mass measurements based on reverberation mapping to within a factor of 2.5 (1,). Finally, the new UV black hole mass estimator is shown to produce identical results to the established optical (H,) estimator when applied to 128 intermediate-redshift (0.3 < z < 0.9) quasars drawn from the Large Bright Quasar Survey and the radio-selected Molonglo quasar sample. We therefore conclude that the new UV virial black hole mass estimator can be reliably used to estimate the black hole masses of quasars from z, 0.25 through to the peak epoch of quasar activity at z, 2.5 via optical spectroscopy alone. [source]

    Ultra-high-resolution observations of circumstellar K i and C2 around the post-AGB star HD 56126

    I. A. Crawford
    We have used the Ultra-High-Resolution Facility (UHRF) at the AAT, operating at a resolution of 0.35 km s,1 (FWHM), to observe K i and C2 absorption lines arising in the circumstellar environment of the post-AGB star HD 56126. We find three narrow circumstellar absorption components in K i, two of which are also present in C2. We attribute this velocity structure to discrete shells resulting from multiple mass-loss events from the star. The very high spectral resolution has enabled us to resolve the intrinsic linewidths of these narrow lines for the first time, and we obtain velocity dispersions (b -values) of 0.2,0.3 km s,1 for the K i components, and 0.540.03 km s,1 for the strongest (and best defined) C2 component. These correspond to rigorous kinetic temperature upper limits of 211 K for K i and 420 K for C2, although the b -value ratio implies that these two species do not co-exist spatially. The observed degree of rotational excitation of C2 implies low kinetic temperatures (Tk,10 K) and high densities (n,106 to 107 cm,3) within the shell responsible for the main C2 component. Given this low temperature, the line profiles then imply either mildly supersonic turbulence or an unresolved velocity gradient through the shell. [source]

    Structural and photoluminescence studies of erbium-implanted nanocrystalline silicon thin films

    M. F. Cerqueira
    Abstract Hydrogenated amorphous and nanocrystalline silicon thin films deposited by hot wire (HW) and radio-frequency plasma-enhanced chemical vapour deposition (RF-PECVD) were erbium-implanted. Their pre-implantation structural properties and post-implantation optical properties were studied and correlated. After 1,h annealing at 150,C in nitrogen atmosphere only amorphous films showed photoluminescence (PL) activity at 1.54,m, measured at 5,K. After further annealing at 300,C for 1,h, all the samples exhibited a sharp PL peak positioned at 1.54,m, with an FWHM of ,5,nm. Amorphous films deposited by HW originated a stronger PL peak than corresponding films deposited by RF, while in nanocrystalline films PL emission was much stronger in samples deposited by RF than by HW. There was no noticeable difference in Er3+ PL activity between films implanted with 1,,1014 and 5,,1015,atoms,cm,2 Er doses. [source]