scholarly journals Competitive X-Ray and Optical Cooling in the Collisionless Shocks of WR 140

2021 ◽  
Vol 923 (2) ◽  
pp. 191
Author(s):  
A. M. T. Pollock ◽  
M. F. Corcoran ◽  
I. R. Stevens ◽  
C. M. P. Russell ◽  
K. Hamaguchi ◽  
...  
Keyword(s):  
Large Scale ◽  
Optical Emission ◽  
Collisionless Shocks ◽  
X Ray ◽  
Band Emission ◽  
Optical Cooling ◽  
Estimate Mass Loss ◽  
Star Binary ◽  
X Ray Absorption ◽  
Rayet Star

Abstract The long-period, highly eccentric Wolf-Rayet star binary system WR 140 has exceptionally well-determined orbital and stellar parameters. Bright, variable X-ray emission is generated in shocks produced by the collision of the winds of the WC7pd+O5.5fc component stars. We discuss the variations in the context of the colliding-wind model using broadband spectrometry from the RXTE, Swift, and NICER observatories obtained over 20 yr and nearly 1000 observations through three consecutive 7.94 yr orbits, including three periastron passages. The X-ray luminosity varies as expected with the inverse of the stellar separation over most of the orbit; departures near periastron are produced when cooling shifts to excess optical emission in C iii λ5696 in particular. We use X-ray absorption to estimate mass-loss rates for both stars and to constrain the system morphology. The absorption maximum coincides closely with the inferior conjunction of the WC star and provides evidence of the ion-reflection mechanism that underlies the formation of collisionless shocks governed by magnetic fields probably generated by the Weibel instability. Comparisons with K-band emission and He i λ10830 absorption show that both are correlated after periastron with the asymmetric X-ray absorption. Dust appears within a few days of periastron, suggesting formation within shocked gas near the stagnation point. The X-ray flares seen in η Car have not occurred in WR 140, suggesting the absence of large-scale wind inhomogeneities. Relatively constant soft emission revealed during the X-ray minimum is probably not from recombining plasma entrained in outflowing shocked gas.

Theoretical and experimental investigation of point defects in cubic boron nitride

MRS Advances ◽  
2017 ◽  
Vol 2 (29) ◽  
pp. 1545-1550 ◽  
Author(s):  
Nicholas L. McDougall ◽  
Jim G. Partridge ◽  
Desmond W. M. Lau ◽  
Philipp Reineck ◽  
Brant C. Gibson ◽  
...  
Keyword(s):  
Boron Nitride ◽  
Cubic Boron Nitride ◽  
Optical Emission ◽  
Wide Band ◽  
Wide Band Gap ◽  
Edge Structure ◽  
X Ray ◽  
Substitutional Defects ◽  
X Ray Absorption ◽  
Annealing Experiments

ABSTRACTCubic boron nitride (cBN) is a synthetic wide band gap material that has attracted attention due to its high thermal conductivity, optical transparency and optical emission. In this work, defects in cBN have been investigated using experimental and theoretical X-ray absorption near edge structure (XANES). Vacancy and O substitutional defects were considered, with O substituted at the N site (ON) to be the most energetically favorable. All defects produce unique signatures in either the B or N K-edges and can thus be identified using XANES. The calculations coupled with electron-irradiation / annealing experiments strongly suggest that ON is the dominant defect in irradiated cBN and remains after annealing. This defect is a likely source of optical emission in cBN.

Characterization of X-ray gas attenuator plasmas by optical emission and tunable laser absorption spectroscopies

2017 ◽  
Vol 24 (6) ◽  
pp. 1195-1208 ◽  
Author(s):  
Álvaro Martín Ortega ◽  
Ana Lacoste ◽  
Stéphane Béchu ◽  
Alexandre Bès ◽  
Nader Sadeghi
Keyword(s):  
Incident Beam ◽  
Tunable Laser ◽  
Optical Emission ◽  
High Energy ◽  
Beam Power ◽  
Beam Path ◽  
Optical Elements ◽  
X Ray ◽  
Laser Absorption ◽  
X Ray Absorption

X-ray gas attenuators are used in high-energy synchrotron beamlines as high-pass filters to reduce the incident power on downstream optical elements. The absorption of the X-ray beam ionizes and heats up the gas, creating plasma around the beam path and hence temperature and density gradients between the center and the walls of the attenuator vessel. The objective of this work is to demonstrate experimentally the generation of plasma by the X-ray beam and to investigate its spatial distribution by measuring some of its parameters, simultaneously with the X-ray power absorption. The gases used in this study were argon and krypton between 13 and 530 mbar. The distribution of the 2pexcited states of both gases was measured using optical emission spectroscopy, and the density of argon metastable atoms in the 1s5state was deduced using tunable laser absorption spectroscopy. The amount of power absorbed was measured using calorimetry and X-ray transmission. The results showed a plasma confined around the X-ray beam path, its size determined mainly by the spatial dimensions of the X-ray beam and not by the absorbed power or the gas pressure. In addition, the X-ray absorption showed a hot central region at a temperature varying between 400 and 1100 K, depending on the incident beam power and on the gas used. The results show that the plasma generated by the X-ray beam plays an essential role in the X-ray absorption. Therefore, plasma processes must be taken into account in the design and modeling of gas attenuators.

scholarly journals Finding and characterising WHIM structures using the luminosity density method

2014 ◽  
Vol 11 (S308) ◽  
pp. 368-371
Author(s):  
Jukka Nevalainen ◽  
L. J. Liivamägi ◽  
E. Tempel ◽  
E. Branchini ◽  
M. Roncarelli ◽  
...  
Keyword(s):  
Large Scale ◽  
Real Data ◽  
Sloan Digital Sky Survey ◽  
Physical Parameters ◽  
X Ray ◽  
Galaxy Surveys ◽  
Sky Survey ◽  
The Galaxy ◽  
Hydrodynamical Simulations ◽  
X Ray Absorption

AbstractWe have developed a new method to approach the missing baryons problem. We assume that the missing baryons reside in a form of Warm Hot Intergalactic Medium, i.e. the WHIM. Our method consists of (a) detecting the coherent large scale structure in the spatial distribution of galaxies that traces the Cosmic Web and that in hydrodynamical simulations is associated to the WHIM, (b) mapping its luminosity into a galaxy luminosity density field, (c) using numerical simulations to relate the luminosity density to the density of the WHIM, (d) applying this relation to real data to trace the WHIM using the observed galaxy luminosities in the Sloan Digital Sky Survey and 2dF redshift surveys. In our application we find evidence for the WHIM along the line of sight to the Sculptor Wall, at redshifts consistent with the recently reported X-ray absorption line detections. Our indirect WHIM detection technique complements the standard method based on the detection of characteristic X-ray absorption lines, showing that the galaxy luminosity density is a reliable signpost for the WHIM. For this reason, our method could be applied to current galaxy surveys to optimise the observational strategies for detecting and studying the WHIM and its properties. Our estimates of the WHIM hydrogen column density NH in Sculptor agree with those obtained via the X-ray analysis. Due to the additional NH estimate, our method has potential for improving the constrains of the physical parameters of the WHIM as derived with X-ray absorption, and thus for improving the understanding of the missing baryons problem.

Uniform Cerium-Based Coordination Polymer Microspheres: Preparation and Upconversion Emission

2016 ◽  
Vol 16 (4) ◽  
pp. 3705-3709 ◽  
Author(s):  
Zhi-Wen Nie ◽  
Cheng-Hui Zeng ◽  
Gang Xie ◽  
Sheng-Liang Zhong
Keyword(s):  
Electron Microscopy ◽  
Coordination Polymer ◽  
Large Scale ◽  
Upconversion Emission ◽  
X Ray Diffraction ◽  
X Ray ◽  
Band Emission ◽  
Transmission Electron ◽  
Light Excitation ◽  
Luminescent Spectra

Homogeneously doped Yb3+ and Er3+ cerium-based coordination polymer (CP) microspheres have been successfully synthesized on a large scale through a simple solvothermal route with 2, 5-pyridinedicarboxylic acid (2, 5-H2PDC) as the organic linker. CeO2:Yb3+, Er3+ porous microspheres were obtained by annealing the corresponding CP microspheres at 600 °C for 4 h under atmospheric pressure. These as-prepared products were characterized by Powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), energy-dispersion X-ray (EDX) spectroscopy, Thermogravimetric (TG) and derivative thermogravimetric (DTG) analysis. The room temperature upconversion luminescent spectra of the as-prepared microspheres were carried out by 980 nm NIR light excitation. Interestingly, Yb3+ and Er3+ codoped CP microspheres give a single-band emission centered at 673 nm, while the CeO2:Yb3+, Er3+ microspheres give emission in green and red region, with red being the dominant emission. The emission intensity of the CeO2:Yb3+, Er3+ microspheres were much stronger than that of the Yb3+ and Er3+ codoped CP microspheres.

scholarly journals Non-negative matrix analysis for effective feature extraction in X-ray spectromicroscopy

2014 ◽  
Vol 171 ◽  
pp. 357-371 ◽  
Author(s):  
Rachel Mak ◽  
Mirna Lerotic ◽  
Holger Fleckenstein ◽  
Stefan Vogt ◽  
Stefan M. Wild ◽  
...  
Keyword(s):  
Large Scale ◽  
Environmental Science ◽  
Matrix Analysis ◽  
Matrix Approximation ◽  
New Approach ◽  
X Ray ◽  
Rich Information ◽  
Preliminary Study ◽  
X Ray Absorption ◽  
Calculated Image

X-Ray absorption spectromicroscopy provides rich information on the chemical organization of materials down to the nanoscale. However, interpretation of this information in studies of “natural” materials such as biological or environmental science specimens can be complicated by the complex mixtures of spectroscopically complicated materials present. We describe here the shortcomings that sometimes arise in previously-employed approaches such as cluster analysis, and we present a new approach based on non-negative matrix approximation (NNMA) analysis with both sparseness and cluster-similarity regularizations. In a preliminary study of the large-scale biochemical organization of human spermatozoa, NNMA analysis delivers results that nicely show the major features of spermatozoa with no physically erroneous negative weightings or thicknesses in the calculated image.

scholarly journals Multi-probe methods for investigating ion hydration

2014 ◽  
Vol 70 (a1) ◽  
pp. C720-C720
Author(s):  
Sofia Diaz-Moreno ◽  
Daniel Bowron
Keyword(s):  
Large Scale ◽  
Biochemical Properties ◽  
X Ray Diffraction ◽  
Ion Hydration ◽  
Neutron Sources ◽  
X Ray ◽  
Chemical Systems ◽  
The Past ◽  
Hydration Shells ◽  
X Ray Absorption

Techniques developed at large scale facilities such as X-ray synchrotrons and pulsed or reactor based neutron sources have, over the past few decades, played a significant role in unravelling many of the mysteries that underpin the chemical, physical and biochemical properties of ions in solutions. In this presentation we will illustrate how the combination of X-ray diffraction, neutron diffraction and X-ray absorption spectroscopy can be applied to the investigation of the structure of ion hydration shells. Examples of hydration of di- and tri-valent ions will be shown. In particular we will present an investigation of the hydration structure of copper (II) ions using this multi-technique approach, and discuss the findings in the context of biological and chemical systems.

Electronic Structure of an [FeFe] Hydrogenase Model Complex in Solution Revealed by X-ray Absorption Spectroscopy Using Narrow-Band Emission Detection

2012 ◽  
Vol 134 (34) ◽  
pp. 14142-14157 ◽  
Author(s):  
Nils Leidel ◽  
Petko Chernev ◽  
Kajsa G. V. Havelius ◽  
Lennart Schwartz ◽  
Sascha Ott ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Absorption Spectroscopy ◽  
Narrow Band ◽  
X Ray ◽  
Band Emission ◽  
Model Complex ◽  
Emission Detection ◽  
X Ray Absorption

scholarly journals Possible Contributions of Supernova Remnants to the Soft X-ray Diffuse Background (0.1 - 1 keV)

1983 ◽  
Vol 101 ◽  
pp. 361-365
Author(s):  
W. T. Sanders ◽  
D. N. Burrows ◽  
D. McCammon ◽  
W. L. Kraushaar
Keyword(s):  
Supernova Remnants ◽  
Large Scale ◽  
Supernova Remnant ◽  
Galactic Halo ◽  
Galactic Plane ◽  
X Rays ◽  
X Ray ◽  
Band Emission ◽  
Diffuse Background ◽  
Almost All

Almost all of the B band (0.10–0.19 keV) and C band (0.15–0.28 keV) X-rays probably originate in a hot region surrounding the Sun, which Cox and Anderson have modeled as a supernova remnant. This same region may account for a significant fraction of the M band (0.5–1 keV) X-rays if the nonequilibrium models of Cox and Anderson are applicable. A population of distant SNR similar to the local region, with center-to-center spacing of about 300 pc, could provide enough galactic M band emission to fill in the dip in the count rate in the galactic plane that would otherwise be present due to absorption of both the extra-galactic power law flux and any large-scale-height stellar (or galactic halo) emission.

Spectroscopic Observations of Baryons in the Local Universe

2005 ◽  
Vol 216 ◽  
pp. 274-289
Author(s):  
Kenneth R. Sembach
Keyword(s):  
Large Scale ◽  
Intergalactic Gas ◽  
Local Universe ◽  
X Ray ◽  
Spectroscopic Observations ◽  
Spectral Diagnostics ◽  
The Galaxy ◽  
X Ray Absorption ◽  
The Universe ◽  
Velocity Cloud

There is increasing observational evidence that hot, highly-ionized interstellar and intergalactic gas plays a significant role in the evolution of galaxies in the local universe. Recent observations from several ultraviolet and X-ray observatories have been used to study the highly ionized high velocity cloud system in the vicinity of the Galaxy, the hot gaseous corona of the Galaxy, and highly ionized absorption-line systems at low redshift. The primary spectral diagnostics of this warm-hot interstellar/intergalactic medium are ultraviolet and X-ray absorption lines of O vi and O vii. The observational data fit well into the framework of current theories for the evolution of large-scale structure in the universe, which predict that a significant fraction of the baryonic material at low redshift is contained in highly ionized intergalactic gas. In this paper, I summarize some of the recent highlights of spectroscopic observations of the hot baryons in the local universe.

scholarly journals High-accuracy mass attenuation coefficients and X-ray absorption spectroscopy of zinc – the first X-ray Extended Range Technique-like experiment in Australia

2021 ◽  
Vol 28 (5) ◽  
Author(s):  
Ruwini S. K. Ekanayake ◽  
Christopher T. Chantler ◽  
Daniel Sier ◽  
Martin J. Schalken ◽  
Alexis J. Illig ◽  
...  
Keyword(s):  
Dark Current ◽  
Large Scale ◽  
Experimental Parameter ◽  
High Accuracy ◽  
Attenuation Coefficients ◽  
X Ray ◽  
Extended Range ◽  
Mass Attenuation Coefficients ◽  
X Ray Absorption ◽  
Mass Attenuation

The first X-ray Extended Range Technique (XERT)-like experiment at the Australian Synchrotron, Australia, is presented. In this experiment X-ray mass attenuation coefficients are measured across an energy range including the zinc K-absorption edge and X-ray absorption fine structure (XAFS). These high-accuracy measurements are recorded at 496 energies from 8.51 keV to 11.59 keV. The XERT protocol dictates that systematic errors due to dark current nonlinearities, correction for blank measurements, full-foil mapping to characterize the absolute value of attenuation, scattering, harmonics and roughness are measured over an extended range of experimental parameter space. This results in data for better analysis, culminating in measurement of mass attenuation coefficients across the zinc K-edge to 0.023–0.036% accuracy. Dark current corrections are energy- and structure-dependent and the magnitude of correction reached 57% for thicker samples but was still large and significant for thin samples. Blank measurements scaled thin foil attenuation coefficients by 60–500%; and up to 90% even for thicker foils. Full-foil mapping and characterization corrected discrepancies between foils of up to 20%, rendering the possibility of absolute measurements of attenuation. Fluorescence scattering was also a major correction. Harmonics, roughness and bandwidth were explored. The energy was calibrated using standard reference foils. These results represent the most extensive and accurate measurements of zinc which enable investigations of discrepancies between current theory and experiments. This work was almost fully automated from this first experiment at the Australian Synchrotron, greatly increasing the possibility for large-scale studies using XERT.

Sign in / Sign up

Export Citation Format

Share Document