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The photoabsorption spectrum of Bi+ was measured in the wavelength range between 37 and 60 nm, using the dual laser plasma technique in which one plasma is used as the source of vacuum ultraviolet continuum radiation and the other plasma is used as the sample of atoms and/or ions to be probed. A number of features in the Bi+ spectrum was identified with the aid of the Cowan suite of atomic codes. The 5d &rarr, 6p transitions from the ground configuration (5d106s26p2) gave rise to the most prominent features in the measured spectrum. Transitions from low-lying excited states associated with the four excited configurations, 5d106s26p6d, 5d106s26p7s, 5d106s26p7p and 5d106s6p3, were found to make small contributions to the observed spectrum in the 47&ndash, 50 nm spectral region. To the best of our knowledge, for Bi+, this spectral region is rather unexplored and spectroscopic data are absent from the literature.

The source responsible for the reionization of the Universe is believed to be the population of star-forming galaxies at $z\sim6$ to 12. The biggest uncertainty concerns the fraction of Lyman-continuum photons that actually escape from the galaxies. In recent years, several relatively small samples of "leaky" galaxies have been uncovered, and clues have begun to emerge as to both the indirect signposts of leakiness and of the conditions/processes that enable the escape of ionizing radiation. In this paper we present the results of a pilot program aimed to test a new technique for finding leaky galaxies---using the weakness of the [SII] nebular emission-lines relative to typical star-forming galaxies as evidence that the interstellar medium is optically-thin to the Lyman continuum. We use the Cosmic Origins Spectrograph on the Hubble Space Telescope to detect significant emerging flux below the Lyman edge in two out of three [SII]-weak star-forming galaxies at $z\sim0.3$. We show that these galaxies differ markedly in their properties from the class of leaky "Green-Pea" galaxies at similar redshifts: our sample galaxies are more massive, more metal-rich, and less extreme in terms of their stellar population and the ionization state of the interstellar medium. Like the Green Peas, they have exceptionally high star-formation rates per unit area. They also share some properties with the known leaky galaxies at $z\sim3$, but are significantly dustier. Our results validate a new way to identify local laboratories for exploring the processes that made it possible for galaxies to reionize the Universe., Accepted for publication in ApJ. 17 pages, 8 figures, 8 tables

The optical to submillimetre continuum radiation of the ISM is polarised by aligned non-spherical dust particles. Modelling of this polarisation spectrum in combination with abundance constraints and simultaneous fit to extinction and emission yields important information on dust grains, including chemistry, mineralogy, particle sizes, and shapes. The pristine nature of dust is better revealed by studying sight-lines that include a single-cloud in the observing beam as compared to attempts at analysing averages of the observing characteristics over multiple-clouds. The propagation of polarised light through dust enshrouded objects is solved by polarisation radiative transfer for which we outline the central methodology.

Nanosecond plasmas in liquids are an important method to trigger the water chemistry for electrolysis or for biomedical applications in plasma medicine. The understanding of these chemical processes relies on knowing the variation of the temperatures in these dynamic plasmas. This is analyzed by monitoring nanosecond pulsed plasmas that are generated by high voltages at 20 kV and pulse lengths of 15 ns applied to a tungsten tip with 50 μm diameter immersed in water. Plasma emission is analyzed by optical emission spectroscopy ranging from UV wavelengths of 250 nm to visible wavelengths of 850 nm at a high temporal resolution of 2 ns. The spectra are dominated by the black body continuum from the hot tungsten surface and line emissions from the hydrogen Balmer series. Typical temperatures from 6000 K up to 8000 K are reached for the tungsten surface corresponding to the boiling temperature of tungsten at varying tungsten vapor pressures. The analysis of the ignition process and the concurrent spectral features indicate that the plasma is initiated by field ionization of water molecules at the electrode surface. At the end of the pulse, field emission of electrons can occur. During the plasma pulse, it is postulated that the plasma contracts locally at the electrode surface forming a hot spot. This causes a characteristic contribution to the continuum emission at small wavelengths.

A new high-resolution radio spectropolarimeter instrument operating in the frequency range of 15 – 85 MHz has recently been commissioned at the Radio Astronomy Field Station of the Indian Institute of Astrophysics at Gauribidanur, 100 km north of Bangalore, India. We describe the design and construction of this instrument. We present observations of a solar radio noise storm associated with Active Region (AR) 12567 in the frequency range of ${\approx}\,15\,\mbox{--}\,85~\mbox{MHz}$ during 18 and 19 July 2016, observed using this instrument in the meridian-transit mode. This is the first report that we are aware of in which both the burst and continuum properties are derived simultaneously. Spectral indices and degree of polarization of both the continuum radiation and bursts are estimated. It is found that The results obtained here indicate that the continuum emission is due to bursts occurring in rapid succession. We find that the derived parameters for Type I bursts are consistent with suprathermal electron acceleration theory and those of Type III favor fundamental plasma emission.

In association with strong solar flares, we sometimes observe enhancements of visible continuum radiation, which is known as a "white-light flare". As most white-light (WL) events show close correlations in time and location with hard X-rays and/or radio emission, there is some consensus that WL emission originates from accelerated particles, especially non-thermal electrons. One model proposes that WL is emitted near the photosphere; however, non-thermal electrons are thermalized in the chromosphere and cannot reach the photosphere. Thus, there is a problem: how can the energy of non-thermal electrons - and/or other accelerated particles such as high-energy protons - propagate to the photosphere and produce WL emission? In the present study, we investigate the possibility that accelerated protons may produce the WL emission of solar flares. We found 51 WL events observed by Hinode/SOT. Among them, gamma-rays with energies greater than 1MeV were observed only in the X1.8-class flare on October 23, 2012 and in the M7.9-class flare on June 25, 2015. Focusing on these flare events, we compare the energetics of WL emission and of accelerated ion fluxes. We find that it is difficult for accelerated ions to provide sufficient energy to account for WL emission.

Recent spacecraft’s observations of kilometric continuum radiation showed that the linear mode conversion theory (LMCT) cannot explain the beaming angle of these observations; on the other hand satellite observations show some local fluctuation in the density gradient. In this research, we consider the mode conversion process from UHR-mode (slow Z- mode) to LO-mode (ordinary) waves, focusing on the effect of the angle between the density gradient and the external magnetic field on the efficiency of the LMCT and the resultant beaming angle of converted LO-mode waves; a comparison of the LMCT and simulation results are presented. We first consider a condition that the density gradient is perpendicular to the external magnetic field, corresponding to the condition assumed in the conventional LMCT. Next, we extend the discussion to the condition that the density gradient is oblique to the external magnetic field. Our aim here is to investigate a condition where the efficient mode conversion can occur and to study the deviation of the beaming angle from that estimated by LMCT. From the results of analyses, for both perpendicular and oblique cases, the highest conversion efficiency is obtained for a certain value of the wave normal angle (critical wave normal angle) of the incident slow Z-mode waves, corresponding to the case when two mode branches are matched. The simulation results show in the perpendicular case that the beaming angle is consistent with the conventional LMCT; but in the oblique case a critical wave normal angle becomes different from the perpendicular case and the beaming angle is different from the LMCT prediction.

This investigation presents and validates a method to visualize CH* chemiluminescence in a sooting non-premixed flame. Excited-state CH radicals (A2Δ → X2Π, denoted CH*), upon relaxing, emit a photon in the visible portion of the electromagnetic spectrum, giving what is seen as a faint blue glow. Optical methods, especially those that rely on passive emission, provide a simple and non-intrusive means to characterize combustion; however, in the presence of hot solid particles – particularly soot – chemiluminescent emission can be obscured by blackbody radiation. This paper describes an image post-processing technique where flame emission is imaged through multiple filters near the CH* emission band in order to infer and filter the contribution of continuum radiation from soot in the CH* band. This information is then used to produce a soot-free image of CH* chemiluminescence.

This paper describes the first part of a project conducted to evaluate the trace element composition of atmospheric aerosol particles (PM2.5) and to determine their influence on air quality in Taif city, Saudi Arabia. PM2.5 particles were collected from two different sites (industrial and residential) in Taif during the summer of 2011. The industrial site was situated in the largest industrial area of Taif, and the residential site was situated in the city’s most crowded area. PM2.5 samples were collected on polycarbonate filters using a cyclonic collector. Each sample was collected over a 24 hour period and new samples were collected weekly. Average PM2.5 concentrations of 47 ± 15 and 46 ± 31 µg/m 3 were seen in the industrial and residential areas, respectively. An Energy Dispersive X-ray Fluorescence (EDXRF) spectrometer with a Mo secondary target was used to analyze the solid samples because of the relative simplicity of the technique for filter analysis. The use of a Mo secondary target is advantageous, because it decreases the impact of continuum radiation from the X-ray tube and increases the signal to background ratio. Quantitative X-ray Analysis Software (PyMca) was used to perform quantitative analysis of the atmospheric aerosols. The analysis resulted in detected concentrations for sixteen elements; Si, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Rb, Sr, Pb and Black Carbon (BC). Using Principal Component Analysis (PCA) it was possible to distinguish between natural and anthropogenic sources. The measured concentrations of the potentially hazardous trace elements Cu, Cr, Mn, Ni and Pb were below the limits defined by international guidelines and national standards for ambient air quality. However, further long-term research will be required to validate the quantification of trace elements in particulate matter in Taif.

Terahertz detectors for astronomical observations such as continuum radiation are required to have a well-defined bandpass, which is typically about 10% of the detector's center frequency. Two cavity bandpass filters with quasi-elliptic response at 220 GHz are therefore analyzed in this paper. A dual-mode cavity bandpass filter is firstly analyzed, showing a limited relative bandwidth of 5.7%. To meet the requirement of 10% relative bandwidth, we proposed a new TE101 cavity bandpass filter incorporating cross electric coupling. Simulation results show that the return loss of the filter is better than −20 dB in a relative bandwidth of 10.7%.

The chapter presents a review of a highly sensitive technique for time-resolved imaging and measurement of the 2D intensity profiles of millimeter waves (MMW) based on the use of visible continuum radiation (VCR) from the positive column (PC) of a medium pressure Cs-Xe DC discharge (VCRD technique). The review focuses on the operating principles, fundamentals, and applications of this new technique. The design of a dis‐ charge tube and an experimental setup which were used to create a wide homogeneous PC plasma slab are described. The MMW effects on the plasma slab are studied. The mechanism of microwave-induced variations in the VCR intensity and the causes of vio‐ lation of the local relation between the visible continuum emissivity and the MMW inten‐ sity are discussed. The main characteristics, e.g., spatial and temporal resolution, and sensitivity of the VCRD technique have been evaluated. Experiments on imaging of the field patterns of horn antennas and quasioptical beams demonstrated that the VCRD technique can be used for a good-quality imaging of the MMW beams in the entire MMwavelength band. The VCRD technique was applied for imaging of output field patterns of the MMW electron tubes and determination of some of their characteristics, as well as for active real-time imaging and nondestructive testing using MM waves.

Early Universe After the universe had cooled into an expanse of neutral gas after the Big Bang, how did the first starlight emerge from the dark? Borthakur et al. found a local starburst galaxy that leaks continuum radiation, which may provide some clues. Wind-generated gaps in the neutral gas enable large fractions of ionizing radiation to escape, possibly mimicking processes in the early universe. Science , this issue p. [216][1] [1]: /lookup/doi/10.1126/science.1254214

Weakly ionized plasmas at or near 1 atm pressure, or atmospheric-pressure plasmas, have received increasing attention due to their scientific significance and potential for use in a variety of applications, particularly for medicine, agriculture, and food. However, there is a large imbalance between scientific research on plasma physics and applications, which is partly due to the considerable differences in the characteristics of these plasmas compared with those of low-pressure plasmas. This discrepancy is particularly related to the difficulty in performing plasma diagnostics for highly collisional plasmas. Information on electrons (such as the electron density and temperature) is essential since electrons play a dominant role in the generation of active species related to the physical and chemical processes inside the plasma. So far, limited diagnostics have been available for electrons such as Thomson scattering and optical emission diagnostics based on equilibrium models. Here, we review the available diagnostic methods along with their merits and limitations for characterizing electrons in weakly ionized collisional plasmas. Particular attention is paid to continuum radiation-based spectroscopy, which facilitates multidimensional imaging of electron density and temperature. The future impact of these plasmas on relevant fields (i.e. laboratory and industrial plasmas and their applications) is also addressed.

We will summarize how future measurements of electromagnetic probes at the upgraded Relativistic Heavy Ion Collider (RHIC-II), in connection with theoretical analysis, can advance our understanding of strongly interacting matter at high energy densities and temperatures. Electromagnetic probes have already played a very important role at SPS and RHIC to date. We will try to identify key physics objectives and observables that remain to be addressed. These include measuring the initial temperature and examining the transition properties via continuum radiation, studying the energy loss mechanism in the medium, the system size evolution via photon-photon correlations as well as medium modifications of vector mesons via low-mass dileptons. We will argue that detector upgrades, increased experimental precision, order of magnitude higher statistics than currently achievable, as well as a detailed scan of colliding species and energies are necessary to allow for sufficient discrimination power in theoretical interpretations.

The molecular continuum radiation of high intensity discharges (HID) containing the rare-earth iodides TmI3, HoI3 and DyI3 in quartz burners have been investigated. For the case of TmI3 a more detailed analysis has been performed. Two main molecular emission contributions have been identified, being located in the arc core and in the mantle region. These molecular emissions turned out to deliver half of the total emission of this type of discharge. The mantle emission was identified as originating from the diatomic TmI. Two distinct upper energy levels at about 4 eV have been determined, being separated about 0.4 eV from each other. A pragmatic approach has been chosen to describe the spectral molecular emission coefficient as a sum of three Gaussian profiles.The proposed method allows one to take into consideration molecular emission for modelling of HID containing rare-earth iodides.

Ultra-high resolution hydrodynamic simulations using 10243 grid points are performed of early supernova burst in a forming galaxy, with properties similar to those inferred for Lyman α emitters (LAEs) and Lyman Break Galaxies (LBGs). We show that, at the earliest stages of less than 300 Myr, continual supernova explosions produce multitudinous hot bubbles and cooled H(I) shells in-between. The H(I) shells radiate intense Lyman α (Lyα) emission like LAEs. We found that the bubbly structures produced are quite similar to the observed features in the Lyα surface brightness distribution of the extended LAEs. After 1 Gyr, the galaxies are dominated by stellar continuum radiation and then resemble the LBGs. At this point, the abundance of heavy elements appears to be solar. After 13 Gyr, these galaxies resemble present-day ellipticals.

The absorption of external radiation and continuum radiation originating from the center in a self-similar expanding gas sphere is considered. The frequency and integral probabilities of radiation absorption in a resonance frequency domain are analyzed depending on the expansion velocity gradient and the optical thickness of the medium. It is demonstrated that the optical density of the medium decreases and the integral absorption increases in the expanding medium.

Infrared (IR) continuum radiation from the arc of high and ultra-high pressure (UHP) mercury lamps was measured and modelled. Three major contributions to the IR continuum are electron-atom bremsstrahlung, which is dominant, electron-ion bremsstrahlung and electron-ion recombination radiation. The line width of the resonance broadened Hg 7 1 S 0 to 6 1 P 1 transition at 1014 nm was used to determine the arc core Hg density, and the radiance of this line was used to determine the arc temperature as a function of radius. The temperature map for the UHP lamp was checked using the Bartels method on the 546 nm line of Hg. Model results based on recently published electron-atom bremsstrahlung coefficients were found to be in good agreement with measurements across the near IR.

The sources for continuum emission are investigated in the visible wavelength range for a high-pressure argon plasma as well as for a high-pressure argon-mercury plasma used for light application. The mechanisms responsible for the continuum emission depend differently on the pressure, the temperature and the ionization degree. By changing these conditions it is shown that one can modify the dominant continuum radiation mechanism. Operational improvement of the high-pressure argon-mercury test lamp are considered with respect to the continuum spectrum in the visible wavelength range.

The Polar spacecraft has identified near-source regions of continuum emission in the plasmapause and outer plasmasphere. As in the case of kilometric continuum (KC), near-source regions of continuum emission often display a high resolution fine structure of closely spaced bands of emission. The separation of the bands is much less than the local gyrofrequency. This suggests that the source is associated with density structures and perhaps the result of trapped eigenmodes. These results imply further that continuum emission is the low-frequency manifestation of KC emission.

Measurements of magnetic fields in solar prominences via Hanle effect usually assume either single scattering approximation or simple, one-dimensional, slab model in order to perform an inversion and find the unknown magnitude and the orientation of the magnetic field from spectropolarimetric observations. Here we perform self-consistent NLTE modeling of scattering polarization in inhomogeneous 2D slab, illuminated from its sides by the solar continuum radiation. We show that even in the absence of a magnetic field, in the non-optically thin regime, significant non-zero Stokes U is to be expected. Neglecting these effects, in principle, could cause systematic errors in spectropolarimetric inversions, in the case when the prominence is optically thick.