Search

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

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.

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.

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.

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.

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 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.

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.

Hot, luminous, massive stars have strong stellar winds driven by line-scattering of the star’s continuum radiation. They are also often observed to exhibit radial or non-radial pulsations. Such pulsations are possible candidates for providing the base perturbations that induce large-scale structure in the overlying wind, and as such they could help explain various observational manifestions of wind variability, e.g., absorption enhancemens or modulations in UV P-Cygni lines of OB stars, and perhaps even moving bumps in optical emission lines of Wolf-Rayet (WR) stars. Here we review the physics of line driving, with emphasis on how perturbations induce variations in a wind outflow. In particular, we present results of a time-dependent dynamical simulation of wind variations induced by the radial pulsation of the β Cep variable BW Vulpeculae, and show that observed variability in UV wind lines can be quite well reproduced by synthetic line profiles for this model. We conclude with a discussion of recent evidence that resonances among multiple modes of non-radial pulsation in Be stars play a role in inducing mass ejections that contribute to formation of a circumstellar disk.

We have monitored the AGN 3C390.3 between 1995 and 2000.Two large amplitude outbursts, of different duration, in continuum and H beta light were observed ie.: in October 1994 a brighter flare that lasted about 1000 days and in July 1997 another one that lasted about 700 days were detected. The flux in the H beta wings and line core vary simultaneously, a behavior indicative of predominantly circular motions in the BLR.Important changes of the Hbeta emission profiles were detected: at times, we found profiles with prominent asymmetric wings, as those normaly seen in Sy1s, while at other times, we observe profiles with weak almost symmetrical wings, similar to those seen in Sy1.8s. We found that the radial velocity difference between the red and blue bumps is anticorrelated with the light curves of H beta and continuum radiation.e found that the radial velocity difference between the red and blue bumps is anticorrelated with the light curves of H-beta and continuum radiation. Theoretical H-beta profiles were computed for an accretion disk, the observed profiles are best reproduced by an inclined disk (25 deg) whose region of maximum emission is located roughly at 200 Rg. The mass of the black hole in 3C 390.3, estimated from the reverberation analysis is Mrev = 2.1 x 10^9 Msun, ie. 5 times larger than previous estimates, Comment: 18 pages, 13 figures, 4 tables. to appear in Astronomy and Astrophysics

From 1996 June 10 to 1996 July 29 the International AGN Watch monitored the Seyfert 1 galaxy NGC 7469 using IUE, RXTE, and a network of ground-based observatories. On 1996 June 18, in the midst of this intensive monitoring period, we obtained a high signal-to-noise snapshot of the UV spectrum from 1150-3300 A using the FOS on HST. This spectrum allows us to disentangle the UV continuum more accurately from the broad wings of the emission lines, to identify clean continuum windows free of contaminating emission and absorption, and to deblend line complexes such as Lya+NV, CIV+HeII+OIII], SiIII]+CIII], and MgII+FeII. Using the FOS spectrum as a template, we have fit and extracted line and continuum fluxes from the IUE monitoring data. The cleaner continuum extractions confirm the discovery of time delays between the different UV continuum bands by Wanders et al. Our new measurements show delays increasing with wavelength for continuum bands centered at 1485 A, 1740 A and 1825 A relative to 1315 A with delays of 0.09, 0.28 and 0.36 days, respectively. Like many other Seyfert 1 galaxies, the UV spectrum of NGC 7469 shows intrinsic, blue-shifted absorption in Lya, NV and C IV. Soft X-ray absorption is also visible in archival ASCA X-ray spectra. The strength of the UV absorption, however, is not compatible with a single-zone model in which the same material absorbs both the UV and X-ray light. Similar to other Seyfert galaxies such as NGC 3516, the UV-absorbing gas in NGC 7469 has a lower ionization parameter and column density than the X-ray absorbing material. While the UV and X-ray absorption does not arise in the same material, the frequent occurrence of both associated UV absorption and X-ray warm absorbers in the same galaxies suggests that the gas supply for each has a common origin.

Linear features of up to 0.25 pc length are seen in both the Helix Nebula and the Orion Nebula. These features are most evident in emission-line ratio images. It is demonstrated that in both objects the features are along projections of lines between the dominant star and an optically thick compact feature (the cometary knots in the Helix and the proplyds in Orion). In general, these features are caused by shadowing of Lyman continuum radiation from the photoionizing star, although in the case of the Helix features, extinction by entrained dust plays a role. Some of the rays have neutral hydrogen cores. It is shown that the characteristics of these linear features can be used to analyze the three-dimensional structure of the nebulae. If the most recent model for these rays is correct and the electron temperature of the shadowed gas is only two-thirds that of the ambient material, then these rays play a small but measurable role in solving the t2 problem.

Recent submillimetre observations of continuum radiation from warm dust and molecular line emission from hot gas in regions of high mass star formation are reviewed. Such regions are characterised by ultracompact HII regions around young OB stars and associated hot molecular cores which appear to harbour high mass protostars at an earlier stage of evolution.

The escape fraction of hydrogen ionizing photons (f_esc) from galaxies has been suggested to be evolving with time, but the picture is far from clear. While evidence for significant escape fractions has been found at high redshifts in several studies, the picture looks different in the more nearby universe. Here, we apply a new background subtraction routine on archival data from the Far Ultraviolet Spectroscopic Explorer (FUSE), in order to study local galaxies in search for possible Lyman Continuum (LyC) leakage. In the process, for the first time a stacked spectrum in the LyC is produced for local galaxies. With this small sample, we also make a more tentative approach to look for possible correlations between f_esc and physical parameters such as internal absorption E(B-V)_i, mass, H I mass, specific star formation rate (SSFR), metallicity, and Ly-alpha emission. Eight star forming galaxies with redshifts z > 0.015 from the FUSE archive were re-examined. Also, a sub-sample of an additional four galaxies with lower redshifts were included, for which the escape fraction was estimated from residual flux in the low ionization interstellar C II(1036{\AA}) line. Out of the eight galaxies, only one was found to have significant LyC leakage, Tol 1247-232 (S/N=5.2). This is the second detection of a leaking galaxy in the local universe. We find an absolute escape fraction for Tol 1247-232 of f_esc = 2.4(+0.9/-0.8) %. The stacked sample show an excess in the LyC with f_esc = 1.4(+0.6/-0.5) %, but we note that there might be important selection biases involved. With the small sample, we suggest a possible trend for higher f_esc with lower mass and with enhanced SSFR. None of the galaxies with high values of E(B-V)_i were found to show any sign of leakage., Comment: Accepted for publication in A&A. 16 pages, 7 pictures

We present uvby β photometry for Be stars in eight open clusters and two OB associations. It is shown that Be stars occupy anomalous positions in the photometric diagrams, which can be explained in terms of the circumstellar continuum radiation contribution to the photometric indices. In the - M V plane Be stars appear redder than the non emission B stars, due to the additional reddening caused by the hydrogen free-bound and free-free recombination in the circumstellar envelope. In the c 0 - M V plane the earlier Be stars present lower c 0 values than absorption-line B stars, which is caused by emission in the Balmer discontinuity, while the later Be stars deviate towards higher c 0 values, indicating absorption in the Balmer discontinuity of circumstellar origin.

We report results of an experimental study focused on the fluorescence of H2 initiated by the impact of quasi-monochromatic electrons. The emission spectra of H2 molecules at electron energies of 25 eV, 50 eV and 100 eV have been measured in the spectral range of 320–670 nm. The emission spectrum is dominated by Balmer emission lines, Fulcher α, β, γ and δ bands and different singlet transitions of H2. In addition to the atomic lines and molecular bands, the presence of continuum radiation is present in the whole studied range. We have determined the emission cross sections (ECS) for particular processes leading to the emission of the Balmer (n = 3, 4, 5, 6, 7, 8 → 2) lines and for selected bands of the Fulcher α system of H2(d 3Πu → a 3 ) as a function of electron energy in the range 5–100 eV. Emission cross sections for the Balmer lines (n = 6, 7, 8 → 2) and Fulcher α (1, 0), (1, 1), (2, 2), (3, 3) bands were measured for the first time.

Using solid, machined $\mathsf{X}$-pinch targets driven by currents rising from 0 to 5--6 MA in 60 ns, we observed bright spots of 5--9-keV continuum radiation from $5\ifmmode\pm\else\textpm\fi{}2\mathrm{\text{\ensuremath{-}}}\ensuremath{\mu}\mathrm{m}$ diameter regions. The $g6\mathrm{\text{\ensuremath{-}}}\mathrm{keV}$ radiation is emitted in about 0.4 ns, and the bright spots are roughly 75 times brighter than the bright spots measured at 1 MA. A total x-ray power of 10 TW peak and yields of $165\ifmmode\pm\else\textpm\fi{}20\text{ }\text{ }\mathrm{kJ}$ were emitted from a 3-mm height. The 3--5-keV continuum radiation had a 50--90-GW peak power and 0.15--0.35-kJ yield. The continuum is plausibly from a $1275\ifmmode\pm\else\textpm\fi{}75\mathrm{\text{\ensuremath{-}}}\mathrm{eV}$ blackbody or alternatively from a $3500\ifmmode\pm\else\textpm\fi{}500\mathrm{\text{\ensuremath{-}}}\mathrm{eV}$ bremsstrahlung source.

Recent maser surveys have shown that many potential OH/IR stars have no OH masers in their circumstellar envelopes, despite the modest requirements which should be implicitly met by IRAS colour-selected candidates. It has been suggested that these OH/IR colour mimics must have a degenerate companion which dissociates OH molecules and disrupts the masing action, ie. that they are related to symbiotic Miras. Coincidentally, there is a paucity of long-period symbiotic Miras and symbiotic OH/IR stars. Phenomonologically, those that are known seem to cluster in the zone where field Miras transform into OH/IR stars. If it could be proven that OH/IR colour mimics contain a degenerate star, that observable evidence of this star is hidden from view by CS dust whilst it slowly accretes from the wind of its Mira companion, then we have an excellent explanation for not only the existence of OH/IR colour mimics, but also for the low observed frequency of symbiotic OH/IR stars and the common occurrence of very slow novae in long-period symbiotic Miras. Here, we employ radio continuum radiation (which should escape unhindered from within the dust shells) as a simple probe of the postulated hot degenerate companions which would inevitably ionize a region of their surrounding gas. We compare the radio and infrared properties of the colour mimics with those of normal symbiotic Miras, using the strong correlation between radio and mid-IR emission in symbiotic stars. We show that if a hot companion exists then, unlike their symbiotic counterparts, they must produce radiation-bounded nebulae. Our observations provide no support for the above scenario for the lack of observed masers, but neither do they permit a rejection of this scenario., 6 pages; no figures attached; LaTeX (MN style); postscript figures via anonymous ftp in users/ers/mimic-figs on astro.caltech.edu; University of Toronto pre-print; ERSRJI3

It has been suggested that continuum radiation from Jupiter could provide the source for the 2- to 3-kHz radio emissions detected by Voyagers 1 and 2 in the outer heliosphere. By a fortuitous set of circumstances the Ulysses flyby of Jupiter in early 1992 provided an opportunity to compare the intensity of a strong, new heliospheric radio emission event with the intensity of continuum radiation from Jupiter. These comparisons show no evidence that Jupiter is the source of the heliospheric radio emissions.

Continuum X-ray emission and fluorescent iron-line emission has been observed from a number of galactic X-ray binaries and from active galactic nuclei. The iron lines and also some features of the continuum result from reprocessing of the continuum radiation of a central source by surrounding matter. Here we calculate by Monte Carlo methods the continuum and line features caused by reprocessing in cold matter of spherical geometry surrounding an X-ray source. The shape of the fluorescent Fe line is useful as a diagnostic of the amount and distribution of the reprocessing matter

One of the main challenges of the implementation of divertor Thomson scattering system on ITER is weak laser scattering signal to be detected against intense background plasma radiation. The paper review briefly the line and continuum radiation data from present magnetic fusion devices in the spectral range of interest to TS diagnostics. The results will form the basis of design and development of the TS diagnostics for the ITER divertor.

The pumping of interstellar methanol masers is studied, covering a range of excitation conditions. The Class I (Class A) masers result from collisional excitation followed by spontaneous radiative decay. Masers appear in low-frequency transitions where the upper state is strongly favoured by large Einstein A coefficients, associated with high-frequency transitions, or by slower loss rates. Absorption (anti-inversion) is seen when the lower state is so favoured. The Class II (Class B) masers appear when there is a source of continuum radiation warmer than the gas kinetic temperature

A detailed investigation of the relationship between the mean atomic number and the intensity of high energy continuum radiation has verified earlier studies in defining a linear relationship. Corrections for matrix effects on the continuum intensity are found to be unnecessary within the precision limits of the data. Incorporation of this relationship into a quantitative energy-dispersive spectrometer (EDS) microanalysis program allows internal correction for electron beam intensity variations between standard and unknown specimen analysis. It therefore allows quantitative analysis without normalisation on systems lacking any form of electron beam current measurement. Within limits, the need for reproducibility of electron beam intensity and counting time is eliminated.

We have developed an experimental setup which allows us to observe weak continuum radiation of collisional quasimolecules involving metal atoms. The setup consists of a tunable pulsed laser used for excitation of metal atoms, a fluorescence cell which contains metal-vapor and foreign-gas mixture, a gated spectrometric multichannel analyzer, and an absorp-tion cell as a filter for suppressing leakeage light of the line core. The setup is described in detail as well as the experimental procedure and results for observing the continuum radiation in far wings of the Yb resonance line which is broadened by collisions with He, Ne, and Ar.

We report an ultra-high-resolution simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation. The bubble structures of gas revealed in our simulation ($< 3\times 10^8$ years) resemble closely the high-redshift Lyman $\alpha$ emitters (LAEs). After $10^9$ years these bodies are dominated by stellar continuum radiation and look like the Lyman break galaxies (LBGs) known as the high-redshift star-forming galaxies at which point the abundance of elements appears to be solar. After $1.3\times10^{10}$ years, these galaxies resemble present-day ellipticals. The comparisons of simulation results with the observations of elliptical galaxies allow us to conclude that LAEs and LBGs are infants of elliptical galaxies or bulge systems in the nearby universe., Comment: To appear in the proceedings of the CRAL-Conference Series I "Chemodynamics: from first stars to local galaxies", Lyon 10-14 July 2006, France, Eds. Emsellem, Wozniak, Massacrier, Gonzalez, Devriendt, Champavert, EAS Publications Series

We have performed IZJHKL' observations in NGC 6611, the young cluster that ionises the Eagle Nebula. We have discovered a rich pre-main sequence concentrated around the O-stars in the cluster. As measured by their L'-band excesses, at least 58% +/- 5% of the pre-main sequence objects (0.45 Msun < M < 2 Msun) have circumstellar discs. By comparing this disc frequency with frequencies determined for regions where the pre-main sequence stars are subject to less ionising radiation, we find no evidence that the harsher environment of NGC 6611 (approximately an order of magnitude more ionising Lyman continuum radiation than the Trapezium cluster) significantly hastens the dissipation of circumstellar discs around solar-mass stars., 4 pages, 3 figures, accepted for publication by MNRAS letters

We present XMM-Newton EPIC observations of warm absorbers in the quasars PG 1114+445 and PG 1309+355, both of which exhibit evidence for absorption by warm material in the line-of-sight. We find the absorption in PG 1114+445 to be in two phases, a `hot' phase with a log ionisation parameter xi of 2.57, and a `cooler' phase with log xi of 0.83; an unresolved transition array (UTA) of M-shell iron is observed in the cooler phase. The absorption in this quasar is similar to that observed in the Seyfert 1 NGC 3783. The absorption in PG 1309+355 consists of a single phase, with log xi of 1.87. The absorbing gas lies at distances of 10^{18} - 10^{22} cm from the continuum radiation sources in these AGN, which suggests that it could originate in a wind emanating from a molecular torus. We derive distances assuming that these X-ray warm absorbers have the same velocity as the UV warm absorbers observed in these quasars. The distances to the warm absorbers from the central continuum source scale approximately with the square root of the AGN ionising luminosity, a result consistent with the warm absorber originating as a torus wind. The kinetic luminosities of these outflowing absorbers represent insignificant fractions (< 10^{-3}) of the energy budgets of the AGN., 11 pages, 5 figures, accepted by MNRAS

Accepted: 2003-03-04, 資料番号: SA1003832000

Periodic or regular flaring of class II methanol masers in nine high mass star forming regions is now a well established phenomenon. Amongst the nine star forming regions, G37.55+0.20 is the only case at present where apart from the presence of a periodic class II methanol maser, correlated flaring of another masing species, formaldehyde in this case, has been detected. We perform numerical calculations to investigate under which conditions the 4.8 GHz transition of ortho-formaldehyde is inverted in order to address the question of the correlated flaring of the 6.7 GHz methanol and 4.8 GHz formaldehyde masers in G37.55+0.20. We developed a numerical code to study the population inversion of o-formaldehyde. Equilibrium solutions for the level populations are found by integrating the rate equations using Heun's method. It is found that collisional excitation with H$_2$ as well as radiative excitation by the free-free radio continuum radiation from a nearby ultra- or hyper-compact HII region can invert the 4.8 GHz transition. It is also found that radiative excitation by the dust infrared radiation field does not lead to an inversion of the 4.8 GHz transition. The 14.5 GHz and 28.9 GHz transitions are inverted only in the presence of the free-free continuum radiation field of a very compact HII region. Due to the different pumping mechanisms of the formaldehyde and methanol masers it is unlikely that the near simultaneous flaring of the methanol and formaldehyde masers in G37.55+0.20 is due to changes in the pumping of the masers., Comment: Accepted for publication in Astronomy and Astrophysics

I show that neutral lithium couples strongly to the cosmic microwave background (CMB) through its 6708A resonant transition after it recombines at z~500. At observed wavelengths of 100). Observations at different wavelengths in this spectral regime can probe different thin slices of the early universe. The anisotropy noise contributed by continuum radiation from foreground far--infrared sources could be taken out by subtracting maps at slightly different wavelengths. Detection of the above effects can be used to study structure at z, Final version. ApJL, in press

We construct a self-consistent model for the wind around W Hya by solving the coupled equations describing the hydrodynamics and dust radiative transfer problems. The model matches simultaneously the observed continuum radiation and wind velocity profile. The water line emission is calculated next using the water abundance as the only free parameter, fitted from the ISO observations of Neufeld et al. (1996) and Barlow et al. (1996). The gas temperature is determined from a thermal balance calculation that includes water as one of its main components. Our model successfully fits all the observed water lines, resolving a major discrepancy between the modeling results of the two observing teams. The mass loss rate is 2.3 x 10^{-6} M_solar yr^{-1}, the water abundance is 1.0 x 10^{-4} and the ortho:para ratio is 1:1.3., Comment: 5 pages, 3 figures, uses aastex.cls and emulateapj5.sty, accepted by ApJ Letters

We report the detection of an optical jet in the nearby Seyfert 1 radio galaxy 3C 120. The optical jet coincides with the well-known radio jet and emits continuum radiation (B,V',I) with a radio-to-optical spectral index of 0.65. There are no clear optical counterparts to the radio knots, although the optical condensation A of the galaxy, which includes the bright 4" radio knot, is found to be 12 % polarized with the electric field vectors perpendicular to the jet. These findings indicate that 3C 120 contains the 6th known extragalactic optical synchrotron jet, quite similar in its properties to the jet of PKS 0521-36. The outer parts of the jet is the faintest known optical jet and was discovered as the result of a dedicated effort to detect it. It is therefore possible that more optical jets can be discovered in systematic searches by combining deep imaging in the optical or near-IR with careful galaxy subtraction methods.

Hot dense plasmas produced when the output of powerful pulsed laser systems are focused onto targets located in vacuum have been the subject of extensive study for a number of years. Such plasmas have found applications both as intense sources of continuum radiation in the XUV and as a versatile source of ionic species. In the work reported here the above properties of the laser produced plasma were exploited and enabled many new photoabsorption spectra of ionic species to be recorded in the XUV region. Using a dual laser produced plasma technique the XUV radiation emitted from laser plasmas created on the surface of a high Z material was used to backlight a second laser plasma and carry out ionic photoabsorption studies at wavelengths below 300A. An extensive examination of a number of isoelectronic sequences was undertaken. XUV photoabsorption studies were carried out on members of the neon, sodium, argon, krypton, bromine, selenium and xenon sequences. Absorption along the neon like sequence was extended to the fifth member, Si V. We report here the first unambiguous photoabsorption spectrum of the neon like A1 ion showing the principal outer shell transitions together with 2s inner shell autoionizing features. Detailed XUV photoabsorption spectra of the Si4+ ion are reported here for the first time, excitations involving an inner 2s electron were classified and m the case of the 2s-»3p transition found to be an example of forced autoionization. An intensity anomaly in the Beutler Fano line shape of the 2s->3p member of the autoionizing series 4 in Si was studied with varying plasma conditions. Absorption studies along the sodium isoelectronic sequence have resulted in the classification of new lines arising from transitions to core excited autoionizing 2 3 levels in the A1 and Si ions, transitions from ground and excited states were observed. XUV photoabsorption spectra of plasmas formed on targets of elements following argon (scandium and titanium) in the periodic table were found to be of a complex nature and to contain contributions from a number of different ion stages. Elements following krypton were also studied. Absorption spectra of laser produced plasmas formed on targets of strontium, yttrium and zirconium were recorded. The strontium and yttrium work resulted m 3d->4p transitions being observed m a number of ion stages for the first time. Work along the xenon sequence was found to be in 2 agreement with previous Ba observations Absorption studies along the sequence were extended to the fifth member Ce4+. An extensive analysis of the 4d photoabsorption spectrum of La was carried out and revealed that the 4d-»4f transition, expected to be the strongest was not observed. The interpretation of the spectrum showed that the feature possessed a large autoionization width and was not present m the experimental spectrum. The analysis further confirmed 2 that the 4f wave function m Ba is only partially collapsed. The work reported here has clearly shown the dual laser produced plasma technique to be a powerful and versatile method for recording XUV photoabsorption spectra of ionized species.

We present the detection of escaping Lyman Continuum (LyC) radiation from two local starburst galaxies, Tol 1247-232 and Tol 0440-381, using archival data from the Far Ultraviolet Spectroscopic Explorer (FUSE). From profile fitting of metal lines, high densities of neutral gas were derived for both galaxies, implying that the LyC radiation is escaping from holes in the interstellar medium. The first results for one of the galaxies, Tol 1247-232, give an escape fraction (fesc) of 17–35%. These new detections, together with that of the blue compact galaxy Haro 11 in Bergvall et al. (2006) where fesc between 4–10% was found, will have a feedback on cosmic reionization models.

We have obtained new optical spectropolarimetric data for the radio-quiet Seyfert NGC 1068, taken through apertures on the nucleus and at two positions within the ionization/scattering cone. The equivalent width of scattered broad-Hβ at these positions, is consistent with the presence of intrinsically beamed continuum radiation.

A correlative survey of magnetometer (MAG) and Planetary Radio Astronomy (PRA) 1.2 kHz continuum radiation measurements from Voyager 2 provide evidence for at least eight distant Jovian magnetotail sightings occurring about once a month over the first 2/3 of 1981 at distances of approximately 5,000 to 9,000 R sub J. The occurrences of these events are in good agreement with prior Plasma Wave Science and Plasma Science identifications. Observations of these distant magnetotail, or tail filament, encounters appear most prevalent in both MAC and PRA data sets when the spacecraft was closest to the Jupiter-Sun axis at approximately 6,500 R sub J from the planet; the PRA events are also most intense during those times. A specific tail encounter occurring in mid-February 1981 is analyzed and shown to possess a remarkably symmetric magnetic field signature and to have a bipolar field structure in the central region. The bipolarity is characteristic of most of the eight events.

The radiation emitted from a wall stabilized helium-plasma (ne ≈ 3 • 1022 m-3, T ≈ 38 000 K, duration of constant discharge current 0.4 ms) was investigated in the wavelength range 300 nm to 650 nm. From the emission coefficients of the continuum radiation Gaunt factors for the state with the principal quantum number 3 and the state 2 3P were determined. Gaunt factors for the terms 2 1S, 2 1P, 2 3S and 2 3P were calculated from the transition probalilities of highly excited states. Agreement to within the accuracy of the measurement was found between the experimental results and the Gaunt factors evaluated from the photoionisation cross-sections calculated by Goldberg. The Gaunt factors for the states 2 1P and 2 3S according to Anderson and Griem are in good agreement with our results; for the terms 2 3P and 2 1S a discrepancy exists. With the Gaunt factors reported here electron densities in a helium-plasma can be determined with a relative uncertainty of 10%. The ξ-factor calculated by Kriener and Schlüter could be confirmed, if Bremsstrahlung of neutral atoms is neglected

Examples of results from a dual satellite (GEOS-1 and ISEE-1) study of terrestrial non-thermal electromagnetic continuum radiation are presented. The problems of sources and generation mechanisms are discussed in the context of simultaneous measurements of radiation arrival directions, radiation cut-offs, and detailed spectral observations. The results, which imply significant contributions from the magnetospheric volume to the low frequency (‘trapped’) component, confirm the near-plasmapause as the source of the higher frequency (‘escaping’) component. The detection of significant X mode radiation and the implied presence of localized non-directive sources lead us to conclude that current theories of generation are inadequate.

The observations of intensity reductions or absorption bursts in the solar decametric radio-continuum are reported. The reductions are interpreted as the absorption of continuum radiation by a shock-generated ion-sound turbulence present in the layer above the continuum level. The duration of the absorption is attributed to the lifetime of the ion-sound turbulence while the depth of absorption is determined by the level of Langmuir waves generated as a result of absorption.