Strong Resonance Lines Research Articles

On the ultraviolet signatures of small scale heating in coronal loops

Studying the statistical properties of solar ultraviolet emission lines could provide information about the nature of small scale coronal heating. We expand on previous work to investigate these properties. We study whether the predicted statistical distribution of ion emission line intensities produced by a specified heating function is affected by the isoelectronic sequence to which the ion belongs, as well as the characteristic temperature at which it was formed. Particular emphasis is placed on the strong resonance lines belonging to the lithium isoelectronic sequence. Predictions for emission lines observed by existing space-based UV spectrometers are given. The effects on the statistics of a line when observed with a wide-band imaging instrument rather than a spectrometer are also investigated. We use a hydrodynamic model to simulate the UV emission of a loop system heated by nanoflares on small, spatially unresolved scales. We select lines emitted at similar temperatures but belonging to different isoelectronic groups: Fe IX and Ne VIII, Fe XII and Mg X, Fe XVII, Fe XIX and Fe XXIV. Our simulations confirm previous results that almost all lines have an intensity distribution that follows a power-law, in a similar way to the heating function. However, only the high temperature lines best preserve the heating function's power law index (Fe XIX being the best ion in the case presented here). The Li isoelectronic lines have different statistical properties with respect to the lines from other sequences, due to the extended high temperature tail of their contribution functions. However, this is not the case for Fe XXIV which may be used as a diagnostic of the coronal heating function. We also show that the power-law index of the heating function is effectively preserved when a line is observed by a wide-band imaging instrument rather than a spectromenter.

Evolution of magnetic correlations in single crystalline La1.2Sr1.8Mn2O7

The electron-spin-resonance measurement for the double perovskite, La1.2Sr1.8Mn2O7 single crystal is carried out from 80 to 450 K. Magnetic phase transitions from the paramagnetic to a mixed state are identified at Tp∼335 K and from mixed to a ferromagnetic state at Tc∼117 K. Two intermediate lines with 2<g<4 are observed within a narrow temperature range (280–340 K), which could be attributed to the magnetic interactions within the double layered perovskite via the interlayer (Mn–O–Mn) and interbilayer (Mn–O–O–Mn) couplings. On the other hand, a strong ferromagnetic resonance line with g=3–6 persists at a wide range of temperature from 340 to 100 K, which linearly varies with temperature and thus attributed to the intralayer (Mn–O–Mn) interaction.

Modeling of the Atomic Processes and Photo Emission of the Plasmas for the EUV Source

A study of the coefficient of radiative transfer of Sn plasmas for the extreme ultra-violet (EUV) light source is presented. The atomic data of near 10 times ionized Sn ions are calculated using the Hullac code, and the emissivity and opacity are calculated using a collisional radiative model, which is used in the radiation hydrodynamics code to calculate the emission spectrum and conversion efficicency. The accuracy of the coefficients of radiative transfer are improved by considering the detailed spectral structure of strong 4d-4f resonance lines, as well as including a large number satellite lines, along with correction of transition wavelength after comparison with spectroscopic measurement.

A Complex Environment around Circinus X‐1

We present the results of an archival 54 ks long Chandra observation of the peculiar source Cir X-1 during the phase passage 0.223-0.261. We focus on the study of detected emission and absorption features using the HETGS. A comparative analysis of X-ray spectra, selected at different flux levels of the source, allows us to distinguish between a very hard state, at a low count rate, and a brighter, softer, highly absorbed spectrum during episodes of flaring activity. The spectrum of the hard state clearly shows emission lines of highly ionized elements, while, during the flaring state, the spectrum also shows strong resonant absorption lines. The most intense and interesting feature in this latter state is present in the Fe Kα region: a very broadened absorption line at energies ~6.5 keV that could result from a smeared blending of resonant absorption lines of moderately ionized iron ions (Fe XX-Fe XXIV). We also observe strong resonant absorption lines of Fe XXV and Fe XXVI, together with a smeared absorption edge above 7 keV. We argue that the emitting region during the quiescent/hard state is constituted of a purely photoionized medium, possibly present above an accretion disk, or of a photoionized plasma present in a beamed outflow. During the flaring states the source undergoes enhanced turbulent accretion that modifies both the accretion geometry and the optical depth of the gas surrounding the primary X-ray source.

The H Lyman- α emission line from the upper atmosphere of Jupiter: Parametric radiative transfer study and comparison with data

This study uses the adding-doubling radiative transfer method in which we take into account the curvature effect of the planetary atmosphere in order to test the sensitivity of the jovian Ly- α emission line in relation to H column density, eddy diffusion coefficient, frequency redistribution function for photon scattering, temperature vertical profile, and an added hot atomic H layer on the top of the atmosphere. We also focus here on developing new diagnostic tools that will help us to obtain more confidently the underlying thermospheric structure of Jupiter. First, using the brightness distribution for specific wavelength bands as proposed by Ben Jaffel et al. [Ben Jaffel, L., Magnan, C., Vidal-Madjar, A., 1988. Astron. Astrophys. 204, 319–326], we show that the spatial thickness of the atomic H layer above the homopause level can be measured directly as the separation between the vertical positions of respectively the line core and line wing optical limbs. This thickness also constrains the [ H ] column and the value K H of the eddy diffusion coefficient at the homopause level at the disc location under consideration. We also propose to refine the value of K H and [ H ] , respectively, at a specific planetary latitude, using the Q ratio of the limb peak brightness to the intensity from other regions over the planetary disc. Finally, the relationship between the disc brightness distribution from specific wavelength bands of the emission line and the temperature gradient in the thermosphere is demonstrated, thus providing an accurate tool to access this key information from high resolution observations. Quick, preliminary comparisons with some existing HTS/STIS data show the H layer thickness at auroral latitudes ( ∼ 1700 km ) is much smaller than at equatorial latitudes ( ∼ 3900 km ). These results strongly support the existence of a gradient in both H density and K H versus latitude, with higher values of K H at high latitudes and higher values of the H density at the equatorial regions. Such a small H layer thickness at auroral latitudes is consistent with a high mixing in the atmosphere that brings the hydrocarbons upwards, reducing consequently the column of hydrogen that scatters photons. These preliminary results show the strength of the proposed approach and open new horizons to use strong resonant emission lines at high resolution as a diagnostic for the state and structure of planetary upper atmospheres.

Atomic modeling of the plasma EUV sources

An atomic model of tin plasmas as a part of the numerical simulation of laser produced plasma (LPP) extreme ultra-violet (EUV) source is presented. The emissivity and opacity of the plasma are calculated and are used in the radiation hydrodynamics simulation. In order to establish a reliable numerical model of the EUV source, which reproduces the experimental emission spectrum and can predict conversion efficiency in 2% bandwidth at λ = 13.5 nm, the wavelengths of strong resonance lines in the model have been improved. The effect of the configuration interaction is investigated theoretically, and the result of calculation is verified through comparisons with detailed spectroscopic measurements. The contribution of satellite lines to the EUV emission is also investigated, along with a heuristic method to determine the dominant emission channels. The multiply and inner-shell excited states of each charge state of tin ions are determined, which have a significant contribution to the ionization balance as well as the emissivity and opacity.

Numerical analysis of energy transport by intense resonance line in Lithium plasmas

Energy transport by a strong resonance line like Lyman α has been studied numerically. The corona region of laser-produced Li plasmas is assumed to be the isothermal expansion model. As a result, though the peak intensity of Lyman α keeps Planckian value, width of the line becomes broader during the transmission in the corona region. If the optical depth could be controlled thicker much more than unity, available power exceeds the value of surface area x intensity of Planckian x line width of emissivity, and the EUV light source for the semiconductor lithography can be designed by Li target.

Beyond the iron group: Heavy metals in hot subdwarfs

We report the discovery of strong photospheric resonance lines of Ga III, Ge IV, Sn iv and Pb iv in the UV spectra of more than two dozen sdB and sdOB stars at temperatures ranging from 22 000 K to 40 000 K. Lines of other heavy elements are also detected, however in these cases more atomic data are needed. Based on these discoveries, we present a hypothesis to explain the apparent lack of silicon in sdB stars hotter than ∼32 000 K. The existence of triply ionised Ge, Sn, and Pb suggests that rather than silicon sinking deep into the photosphere, it is removed from the star in a fractionated stellar wind. This hypothesis provides a challenge to diffusion models of sdB stars.

Microchip laser-induced breakdown spectroscopy: a preliminary feasibility investigation.

A commercial, 7 microJ/pulse, 550 ps microchip laser is used to induce plasma on Pb, Si, Cu, Fe, Ni, Ti, Zn, Ta, and Mo foils and a Si wafer. The measured plasma lifetime is comparable with the duration of the laser pulse (a few ns). The plasma continuum radiation is low, while some of the strong resonance lines (e.g., Zn 213.86 nm) show self-reversal. Quantitative analysis is possible using non-gated detectors but analytical lines should be chosen with care to avoid reduction in the linear dynamic range. The mass removed (0.5-20 ng/pulse) is sufficient to yield spectra that are detectable with portable grating spectrometers equipped with non-gated, non-intensified detector arrays. The spectrum of Cd is detected with a broadband portable spectrometer (200-950 nm). The combination of the broadband spectrometer and the microchip laser is very promising for material identification, especially in field applications.

Detection of Nitrogen and Neon in the X-Ray Spectrum of GP Comae Berenices with XMM/Newton

We report on X-ray spectroscopic observations with XMM/Newton of the ultracompact, double white dwarf binary GP Com. With the Reflection Grating Spectrometers (RGSs), we detect the Lyα and Lyβ lines of hydrogen-like nitrogen (N VII) and neon (Ne X), as well as the helium-like triplets (N VI and Ne IX) of these same elements. All the emission lines are unresolved. These are the first detections of X-ray emission lines from a double-degenerate, AM CVn system. We detect the resonance (r) and intercombination (i) lines of the N VI triplet, but not the forbidden (f) line. The implied line ratios for N VI, R = f/i < 0.3 and G = (f + i)/r ≈ 1, combined with the strong resonance line are consistent with formation in a dense, collision-dominated plasma. Both the RGS and EPIC/MOS spectra are well fitted by emission from an optically thin thermal plasma with an emission measure proportional to (kT/6.5 keV)0.8 (model cevmkl in XSPEC). Helium, nitrogen, oxygen, and neon are required to adequately model the spectrum; however, the inclusion of sulphur and iron further improves the fit, suggesting that these elements may also be present at low abundance. We confirm in the X-rays the underabundance of both carbon and oxygen relative to nitrogen, first deduced from optical spectroscopy by Marsh et al. The average X-ray luminosity of ≈3 × 1030 ergs s-1 implies a mass accretion rate ≈ 9 × 10-13 M☉ yr-1. The implied temperature and density of the emitting plasma, combined with the presence of narrow emission lines and the low- value, are consistent with production of the X-ray emission in an optically thin boundary layer just above the surface of the white dwarf.

Observations of the Star-Disk Interface: Search for Wind Origins

Energetic outflows provide a dramatic accompaniment to accretion disks in all stages of star formation. The low extinction toward Classical T Tauri stars offers an opportunity to probe the star-disk interface region to search for the launch site and acceleration region of accretion-driven winds. This search is complicated by the fact that the dominant sources of emission in the optical and ultraviolet are the funnel flows and accretion shocks associated with magnetospheric accretion. Thus the quest for inner wind diagnostics requires disentangling accretion and outflow processes from the same line profile. We discuss two tracers of a high velocity inner wind in stars with high disk accretion rates. One, a hot component, is traced by helium emission and must arise very close to the star. A second, cooler component, is traced by blueshifted absorption in strong resonance lines and arises further from the star, but still within about ten stellar radii. We present evidence that the character of both magnetospheric accretion and the inner wind may differ among stars with high and low disk accretion rates.

On the Physical Origin of OviAbsorption‐Line Systems

We present a unified analysis of the O VI absorption lines seen in the disk and halo of the Milky Way, high-velocity clouds, the Magellanic Clouds, starburst galaxies, and the intergalactic medium. We show that these disparate systems define a simple relationship between the O VI column density and absorption-line width that is independent of the oxygen abundance over the range O/H ~ 10% to twice solar. We show that this relation is exactly that predicted theoretically as a radiatively cooling flow of hot gas passes through the coronal temperature regime?independent of its density or metallicity (for O/H 0.1 solar). Since most of the intergalactic O VI clouds obey this relation, we infer that they cannot have metallicities less than a few percent solar. In order to be able to cool radiatively in less than a Hubble time, the intergalactic clouds must be smaller than ~1 Mpc in size. The implied global heating rate of the warm/hot intergalactic medium is consistent with available sources. We show that the cooling column densities for the O IV, O V, Ne V, and Ne VI ions are comparable to those seen in O VI. This is also true for the Li-like ions Ne VIII, Mg X, and Si XII (if the gas is cooling from T 106 K). All these ions have strong resonance lines in the extreme-ultraviolet spectral range and would be accessible to Far Ultraviolet Spectroscopic Explorer at z 0.2-0.8. We also show that the Li-like ions can be used to probe radiatively cooling gas at temperatures 1 order of magnitude higher than where their ionic fraction peaks. We calculate that the H-like (He-like) O, Ne, Mg, Si, and S ions have cooling columns of ~1017 (a few times 1016) cm-2. The properties of the O VII, O VIII, and Ne IX X-ray absorption lines toward PKS 2155-304 may be consistent with a scenario of radiatively cooling gas in the Galactic disk or halo.

Far Ultraviolet Spectroscopic Explorer and Hopkins Ultraviolet Telescope Observations of Radiative Shocks in the Cygnus Loop

We report a combination of high and low spectral resolution far-ultraviolet spectral data for several groupings of bright radiative shock filaments in the Cygnus Loop supernova remnant. The high-resolution spectra were obtained with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite and cover the 905-1187 A spectral region at 0.1-0.3 A resolution, depending on observing aperture. The low-resolution data were obtained with the Hopkins Ultraviolet Telescope (HUT) and cover the 850-1850 A spectral region at ~3 A resolution. These data sets complement each other, with the HUT data providing the broader context of a wider range of emission lines and the FUSE data resolving line profiles from nearby airglow emissions and allowing detailed line profiles to be studied. Relative line intensities and line profiles change on a wide variety of spatial scales. O VI λλ1032, 1038 emission is much more generally distributed than the optical filaments. The FUSE data provide direct insight into the effects and variability of self-absorption in the strong resonance lines of O VI and C III λ977. Variability of the central reversals in O VI with position indicate a patchy O VI distribution, with self-absorption occurring locally within the remnant. Self-absorption in C III could be due to the interstellar medium, the local regions of the remnant, or a combination. We also find evidence for overlying molecular hydrogen absorption effects on some lines and suggest an interstellar (foreground) origin. It is likely that these effects have had significant impacts on many previous investigations that based their results on the interpretation of low-resolution spectral data where these effects could not be seen.

Feasibility study of a low pressure barium discharge lamp

We report the results of an experimental and theoretical study on the feasibility of a barium low pressure discharge as a potential new light source. Barium has a strong neutral resonance line at 553.5 nm, near the center of the eye’s response curve, as well as several red and blue lines from barium ions. Due to the strong reactivity of barium with a wide variety of standard lamp materials, experiments were performed in arc tubes lined with yttria (Y2O3). A wide range of parameter space was explored in buffer gas pressure (1–30 Torr), gas type (argon, neon, and krypton), barium temperature (400–760 °C), and arc current (0.05–1.0 A). The numerical model qualitatively predicted the influence of these parameters on light output. However, the predicted efficacies of up to 100 lm/W were considerably higher than the measured values. The best positive column efficacy achieved was 50 lm/W in a sealed yttria lined quartz tube with 5 Torr argon operating at 400 mA at 760 °C. Possible reasons for this discrepancy are discussed.

On the nature of the hard X-ray source 4U 2206+54

The recent discovery of a9:5d period in the X-ray lightcurve of the massive X-ray binary 4U 2206+54 has opened the possibility that it is a Be/X-ray binary with an unusually close orbit, which, together with its low intrinsic luminosity, suggests that the system is actually a Be + WD binary, in which a white dwarf accretes material from the dense circumstellar disc surrounding a classical Be star. In this paper we present new X-ray observations and for the rst time high-resolution optical spectroscopy of the source. We show that both the X-ray behaviour and the characteristics of the optical counterpart, BD +53 2790, are more consistent with a neutron star accreting from the wind of an early-type star. The X-ray lightcurve shows irregular flaring and no indications of pulsations, while the very high hydrogen column density supports accretion from a dense wind. BD +53 2790 is shown not to be a classical Be star, as believed until now, but rather a very peculiar late O-type active star, exhibiting emission components in the He ii lines, complex spectral variability and strong wind resonance lines in the ultraviolet. Though many of the characteristics of the spectrum resemble those of the He-rich stars, the absence of He i variability makes a connection unlikely. The spectrum is compatible with a composite of two stars of similar spectral type, though circumstantial evidence points to a single very peculiar active early-type star. This adds weight to the growing evidence that the traditional subdivisions of supergiant and Be/X-ray binaries fail to cover the whole phenomenology of massive X-ray binaries.

Investigation of biomass- and polymer-based carbon materials using 13C high-resolution solid-state NMR

Carbon materials produced through the thermal decomposition of biomass (rice hulls) and a polymer (polyvinyl chloride) were investigated by 13C high-resolution solid-state NMR under two different magnetic fields (2.0 and 9.4 T). The details revealed by the high-field NMR spectra provide important information about the chemical changes in the initial stages of pyrolysis: These are shown to be directly related to the original structure of the precursors and the results complement well some conclusions existent in the literature. From a heat treatment temperature of about 600°C upwards, the general shape of the 13C NMR spectra, attained with low applied magnetic field, is very similar for both chars, with a strong resonance line near 125 ppm from TMS (carbon nuclei in aromatic planes). The analysis of the evolution of the main parameters associated with this resonance line shows a behavior typical of heat-treated carbon materials, which is interpreted on the basis of the structural evolution of both chars. We show that the results are well understood when a comparison is made with the features of the 13C NMR spectrum of polycrystalline graphite.

HD 172481: A super lithium-rich metal-deficient post-AGB binary with a red AGB companion

We present in this paper a study on the peculiar supergiant HD 172481. Its spectral type (F2Ia), high galactic latitude (b = -10 fraction of degree37), circumstellar dust, high radial velocity and moderate metal deficiency ([Fe/H] = -0.55) confirm the post-AGB character of this object. A detailed chemical analysis shows slight but real s-process overabundances, however no CNO-enhancement was detected. Furthermore, the spectral energy distribution and the TiO bands in the red part of the spectrum reveal a red luminous companion. The luminosity ratio of the hot F type component and this cool M type companion is derived for a reddening of () and indicates that the companion must also be strongly evolved and probably evolving along the AGB. Neither our photometric data-set, nor our radial velocity monitoring show evidence for orbital variability which may indicate that the period is too large for direct binary interaction. Most interestingly, a strong lithium resonance line is detected, which yields an abundance of = 3.6. Several explanations for this large lithium content are explored.

Intracavity UV-range laser spectrometer

We suggest a variant, which has already been implemented, of a selective intracavity laser spectrometer with intracavity nonlinear optical conversion of the frequency range of generated multimode radiation. The apparatus provides a means for transition into the UV spectral range (shorter than 300 nm) to carry out direct recording and quantative investigation of strong resonance lines of atomic absorption, which earlier were beyond the reach of the intracavity method. We measured selective absorption in spectral lines of a number of metals: FeI 296.690 nm, TiI 294.200 nm, and GaI 287.424 nm.

Calculation of Solar Irradiances. I. Synthesis of the Solar Spectrum

Variations in the total radiative output of the Sun as well as the detailed spectral irradiance are of interest to terrestrial and solar-stellar atmosphere studies. Recent observations provide measurements of spectral irradiance variations at wavelengths in the range 1100-8650 ? with improved accuracy, and correlative studies give procedures for estimating the spectral irradiance changes from solar activity records using indicators such as those derived from Ca II K and Mg II indices. Here we describe our approach to physical modeling of irradiance variations using seven semiempirical models to represent sunspots, plage, network, and quiet atmosphere. This paper gives methods and details, and some preliminary results of our synthesis of the variations of the entire irradiance spectrum. Our calculation uses object-oriented programming techniques that are very efficient and flexible. We compute at high spectral resolution the intensity as a function of wavelength and position on the disk for each of the structure types corresponding to our models. These calculations include three different approximations for the line source function: one suited for the very strong resonance lines where partial redistribution (PRD) is important, another for the most important nonresonance lines, and another approximation for the many narrow lines that are provided in Kurucz's listings. The image analysis and calculations of the irradiance variation as a function of time will be described in a later paper. This work provides an understanding of the sources of variability arising from solar-activity surface structures. We compute the Ly? irradiance to within 3% of the observed values. The difference between our computations and the Neckel & Labs data is 3% or less in the near-IR wavelengths at 8650 ?, and less than 1% in the red at 6080 ?. Near 4100 ? we overestimate the irradiance by 9%-19% because of opacity sources missing in our calculations. We also compute a solar cycle variability of 49% in the Ly? irradiance, which is very close to observed values. At wavelengths between 4100 ? and 1.6 ?m, we obtain spectral irradiance variations ranging from -0.06% to 0.46% in the visible?the higher values correspond to the presence of strong lines. The variability in the IR between 1.3 and 2.2 ?m is ~-0.15%.

Dose- and annealing-induced changes in the microstructure of buried SiNx: An x-ray absorption study

The microstructure and the annealing behavior of N-rich SiNx films are studied with x-ray absorption measurements at the N-K edge. The SiNx films were fabricated with ion implantation of 35 keV N+ ions into Si substrates, in the dose range 2×1017–2×1018 ions/cm2. The near-edge x-ray absorption fine structure (NEXAFS) spectra of the N-rich films are characterized by a strong resonance line (RL2) at 403.3±0.1 eV whose intensity increases with the implantation dose. RL2 is attributed to dipole electron transitions, from 1s to unoccupied p orbitals, at a defect site containing a N dangling bond defect. The defect related to RL2 has high thermal stability and is practically unaffected by vacuum annealing up to 1000 °C. One more defect-related resonance (RL1) is detected at 401.1±0.3 eV in the films fabricated with the lower and intermediate used implantation doses (2×1017 and 1×1018 cm−2, respectively). The activation energy for the annealing of RL1 is 0.50±0.05 eV. Extended x-ray absorption fine structure spectroscopy (EXAFS) on the as-implanted and annealed films reveals that subnitrides are formed upon implantation. These nitrides are characterized by a Si-N nearest-neighbor distance which is comparable to that of the reference nitride, while the coordination number in the first nearest-neighbor shell N1 depends on the implantation dose. The stoichiometry deviation, as measured from the value of N1 which takes values between 1.7 and 2.8 for the limiting doses of 2×1018 and 2×1017 cm−2, respectively, shows the correlation between the RL2 in the NEXAFS spectra and the presence of N dangling bonds in the as-implanted films.