VII Line Research Articles

Analysis of the 5d5f configuration of Os VII and Ir VIII

The spectra of osmium and iridium were photographed in the 200-400 Å region on a 3 m normal incidence and 10.7 m grazing incidence spectrographs. The light sources used were triggered and sliding sparks. The 5d2-5d5f transitions in Os VII and Ir VIII were analysed. Eighteen of 20 levels of the 5d5f configuration in each spectrum have been established. Seventy-two lines of Os VII and 58 lines of Ir VIII have been classified. Least-squares fitted (LSF) and Hartree-Fock (HF) calculations were carried out to interpret the observed spectra.

Si VII line ratio diagnostics for CDS

We present new calculations for Si VII line ratio density diagnostics and suggest some observable lines, hitherto not observed, for observations to be obtained with the Coronal Diagnostic Spectrometer (CDS) on board the SOHO mission.

High-power imploding plasma for the X-ray laser

The Al–Mg photoresonant X-ray laser scheme study was carried out on the 1.4-MA GIT-4 generator with a 1.7-cm separation between the liner axis and the Mg target. The radiation power in the pumping line was (2–3).109 W/cm and the radiation power within the 45–60–A range was 3.11010 W/cm. The Mg VI and MG VII lines were found by the grating spectrograph.

The effect of high-Z atomic radiators on the x-ray emission rate from a laser-produced nitrogen plasma

The effect of a small admixture of high-Z atomic radiators on the radiation rate of a laser-produced nitrogen plasma has been experimentally studied for application to a nitrogen recombination soft x-ray laser. The experiments used a miniature supersonic gas jet as a laser target that is capable of producing an on-axis density of 1×1019 atoms/cm3. Nitrogen gas was seeded with 1%, 2%, and 5% (by number) of Ar, Kr, and Xe and irradiated with 31 J, 3 ns full width at half maximum pulses of 1054 nm light. The time-dependent intensity of x rays between 114 and 140 Å was measured from these plasmas and it was found that the e−1 decay time decreased with increasing Z and with the concentration of the high-Z radiator. Several time-integrated N VII spectral lines relevant to a nitrogen soft x-ray laser are plotted against the measured e−1 decay time and it was found that the N VII line at 133.8 Å is observed to be unusually bright as compared to the N VII 4-2 and 2-1 transitions, suggesting that enhanced recombination effects are possibly being seen. In addition, theoretical calculations of the N VII first- and second-excited state population dynamics are presented that predict a population inversion in recombining nitrogen, indicating a small signal gain of 4.4 cm−1. It is concluded that a low-Z soft x-ray laser is feasible using a laser-heated gas jet target and that possible gain enhancement might be possible by adding high-Z radiators to increase the cooling rate of the plasma.

Density measurements of a neon Z-pinch plasma

The absolute intensity of near-ultraviolet emission from a neon Z-pinch plasma is measured with a time-gated, two-dimensional optical multichannel analyzer (OMA). The OMA provides spatial and spectral resolution with a 100 ns gate duration. Spatially resolved continuum emission, Ne viii line emission, and Ne viii line-profile measurements are used to determine the pinch diameter, the density of the neon plasma, and the Ne viii 3p level population.

Fluorescence in Mg IX emission at 48.340 Å from Mg pinch plasmas photopumped by Al XromanI line radiation at 48.338.

Resonant photopumping of Be-like Mg ix ions by Li-like Al xi line radiation has been studied in pulsed-power-driven plasmas as a possible approach to achieve laser action in the extreme-ultraviolet wavelength region. An Al x-pinch or z-pinch plasma imploded by a 0.5-TW pulsed power generator produced intense line radiation at 48.338 \AA{}. A separate Mg z-pinch plasma, driven by the same pulsed power generator, was created in parallel with 1 cm separating the two plasmas. Evidence for fluorescence (resonant scattering) was the appearance of 48.340-\AA{} resonance line emission from the 4p level of Mg ix ions due to photopumping by the Al xi line radiation at 48.338 \AA{}. Fluorescence may also have been observed on the Mg viii line at 52.395 \AA{}, photopumped by Al xi line radiation at 52.446 \AA{}. Both Al and Mg plasmas were characterized in the experiments. Improvements to the pump geometry required to achieve gain on the Mg ix line at 228 \AA{} are also discussed.

The presence of Fe VII and of low-ionization features in the UV spectra of central stars of planetary nebulae

The correlation between the presence of N I and Fe VII absorption lines in the spectra of central stars of planetary nebulae reported by Feibelman & Bruhweiler and Cheng, Feibelman & Bruhweiler is refuted. Many spectra that they discuss are severely underexposed; moreover, 12 of them reveal no continuum whatsoever. These therefore cannot be used in the discussion of the presence or absence of absorption lines. Contrary to their claim that the Fe VII lines bear no relation to central-star properties, these lines correlate strongly with photospheric temperature. N I appears in all the spectra which have at least moderately well exposed continua, and a correlation between the equivalent width of the 1200-A triplet and the surface gravity of the central star―which can be interpreted as an age index of the star―is shown to be a selection effect

The spectrum and term system of He-like O VII

The spectrum of He-like O VII has been studied at the ISX-A tokamak in Oak Ridge. In the region 15-140 Å about 20 O VII lines were measured. The results were combined with previous data to derive an energy level diagram for O VII. The ionization energy was determined to 5 963 078 ± 175 cm-1. This value is in agreement with previous experimental results but the uncertainty has been significantly reduced. A comparison with theoretical calculations yields a value of 440 ± 175 cm-1 for the QED contribution ("Lamb shift") to the 1s2 1S0 ground term energy, in good agreement with theoretical predictions.

The central star of S 216

Optical and high-resolution ultraviolet spectra of LS V+46 21, the postulated central star of the large, nearby planetary nebula S 216, have been analysed. From modelling the line profiles, this star is found to have an effective temperature ≃90 000 K, surface gravity log g∼7, and a He:H ratio ∼0.01. These are as expected from published data on the nebula, and provide confirmation that it is a planetary. The ultraviolet data reveal a spectrum rich in lines of Fe VI and Fe VII, whose excitation potentials require a photospheric origin. LS V+46 21 is currently the brightest member of the DAO class of white dwarfs and planetaries

Ultraviolet Fe VII absorption and Fe II emission lines of central stars of planetary nebulae

The SWP camera of the IUE satellite was used in the high-dispersion mode to search for Fe VII absorption and Fe II high-excitation emission lines in five additional very hot central stars of planetary nebulae. Some of the Fe VII lines were detected at 1208, 1239, and 1332 A in all the objects of this program, LT 5, NGC 6058, NGC 7094, A43, and Lo 1 (= K1-26), as well as some of the Fe II emission lines at A 1360, 1776, 1869, 1881, 1884, and 1975 A. Two additional objects, NGC 2867 and He 2-131, were obtained from the IUE archive and were evaluated. The present study probably exhausts the list of candidates that are sufficiently bright and hot to be reached with the high-dispersion mode of the IUE.

Ultraviolet Fe VII absorption lines in planetary nebula nuclei, hot subdwarfs, and hot degenerate objects

view Abstract Citations (34) References (40) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Ultraviolet Fe VII Absorption Lines in Planetary Nebula Nuclei, Hot Subdwarfs, and Hot Degenerate Objects Feibelman, Walter A. ; Bruhweiler, Frederick C. Abstract Results are reported from a search for Fe VII absorption lines in data from high-dispersion IUE-SWP observations of PN nuclei (PNN), hot subdwarfs (HSDs), and hot white dwarfs (HWDs). The data-reduction techniques employed are outlined, and the results are presented in extensive tables and sample spectra and characterized in detail. Absorption in at least one of the four Fe VII lines above 120 nm wavelength is found in 22 of 51 PNN, and possibly in 10 HSDs, in the pulsating HWD PG 1159 - 035, and in the PNN K1 - 16. It is concluded that Fe VII is more common in WD progenitors such as PNN than previously predicted and is especially typical of the more luminous low-gravity stars. Publication: The Astrophysical Journal Pub Date: July 1990 DOI: 10.1086/168942 Bibcode: 1990ApJ...357..548F Keywords: Hot Stars; Planetary Nebulae; Subdwarf Stars; Ultraviolet Spectra; White Dwarf Stars; Absorption Spectra; Iue; Line Spectra; Stellar Winds; Astrophysics; NEBULAE: PLANETARY; STARS: SUBDWARFS; STARS: WHITE DWARFS; ULTRAVIOLET: SPECTRA full text sources ADS | data products SIMBAD (63) MAST (1) INES (1)

Features in the Soft X-ray Background

AbstractThe soft X-ray background is explained in terms of emission coming from hot gas. Most of these soft X-ray data were obtained by proportional counters with a poor energy resolution. Instruments having the capability to resolve lines were only flown by two groups: a GSPC by a Japanese group and a SSD by a french-american collaboration. They both detected the 0 VII line emission coming from the soft X-ray background and so proved the thermal nature of the emission. The implications of these results on possible models for the local hot medium will be discussed. The same detectors observed part of the North Polar Spur. They detected emission lines coming from different species (0 VII,Fe XVII,Ne IX). Spatial variations of line ratios for this object could be due to non-equilibrium ionization effects.

Dynamic evolution of the source volumes of gradual and impulsive solar flare emissions

This study compares flare source volumes inferred from impulsive hard X-rays and microwaves with those derived from density sensitive soft X-ray line ratios in the O VII spectrum. The data for this study were obtained with the SMM Hard X-ray Burst Spectrometer, Earth-based radio observatories, and the SOLEX-B spectrometer on the P78-1 satellite. Data were available for the flares of 1980 April 8, 1980 May 9, and 1981 February 26. The hard X-ray/microwave source volume is determined under the assumption that the same electron temperature or power law index characterizes both the source of hard X-rays and the source of microwaves. The O VII line ratios yield the density and volume of the 2 x 10 to the 6th K plasma. For all three flares, the O VII source volume is found to be smallest at the beginning of the flare, near the time when the impulsive hard X-ray/microwave volume reaches its first maximum. At this time, the O VII volume is three to four orders of magnitude smaller than that inferred from the hard X-ray/microwave analysis. Subsequently, the O VII source volume increases by one or two orders of magnitude then remains almost constant until the end of themore » flare when it apparently increases again. 29 references.« less

Detection of highly ionized silicon in the planetary nebulae NGC 6302 and NGC 6537

Observations of two high-excitation helium-rich PNs are reported, showing Si VI and Si VII near-IR forbidden line emission from NGC 6302 and forbidden Si VI line emission from NGC 6537. The fluxes observed from NGC 6302 are 3.8 X 10 to the -11 ergs/sq cm sec for the forbidden Si VI line at 1.96 microns and 4.3 X 10 to the -11 ergs/ sq cm sec for the forbidden Si VII line at 2.48 microns. Abundances for Si (5+) and Si (6+) are derived and the central star temperatures are estimated using the abundance ratio. It is found that NGC 6302 probably has the hottest central star of any planetary that has been observed. 39 references.

Lifetimes and oscillator strengths of singly ionized vanadium

Lifetimes of 12VII levels have been measured by using the technique of laser-excited fluorescence from sputtered metal vapour. The uncertainty is between 7–9%. For a determination of the individual transition probabilities the corresponding emission branching ratios have been measured on a high-current hollow-cathode in conjunction with a 1 m Fourier-transform spectrometer. Thef-values of 86 VII lines, which cover a spectral range 260–420 nm, have an uncertainty of about 12%. Comparison is made with literature data.

Determination of transition probabilities for singly ionized vanadium

Transition probabilities of 211 spectral lines of VII, in the wavelength range 2340–4200 Å, have been determined by emission spectroscopy using a wall-stabilized arc as source. The lines studied belong to the transition arrays 3 d 4, 3 d 3 4s-3 d 34 p (199 lines) and 3 d 34 p-3 d 34 d, 3 d 35 s (12 lines). Vanadium was introduced into the helium-arc discharge as the liquid VOCl 3. An important feature of this work is the determination of transition probabilities for many lines from a wide spectral range with a uniform absolute scale. The absolute A ki values were obtained by normalizing relative A ki values to an absolute scale set by ionic lifetime for the level y 3 H 0 4. These results are compared with other experimental as well as theoretical results.

MARKARIAN 1388 - A HIGH-IONIZATION NARROW-LINE SEYFERT GALAXY.

ABSTRACT The spectrum of the Seyfert galaxy Mrk 1388 is described. It is unusual in having strong high-ionization lines (in particular, the forbidden lines of Fe VII and Fe X) and a strong featureless continuum, but narrow H I lines with essentially the same widths as the forbidden lines. The spectrum thus combines characteristics usually found separately in Seyfert 1 and Seyfert 2 galaxies.

The Spectrum of Six Times Ionized Fluorine

The spectrum of F VII has been studied between 400 and 6000 Å by the beam-foil method. In this interval 48 F VII lines have been identified. The analysis includes also 39 lines below 200 Å from an unpublished wavelength list from Edlén. From these lines, 35 energy levels have been determined and the whole term system is described by Ritz formulae and by using the polarization parameterization. The ionization energy is determined to 1 493 632 ± 5 cm-1.The experimentally determined energy levels are found to be in good agreement with the values predicted by Edlén (Physica Scripta, 19, 255 (1979)) in a study of the Li I isoelectronic sequence.In addition five F VIII lines are also reported.

The Local Hot Bubble from X-Ray Spectroscopic Measurements

Soft X-ray surveys proved the existence of a local hot bubble surrounding the solar system. Recently two experiments measured the spectrum of this hot interstellar medium with solid state detectors during rocket flights between 300 and 1000 eV [4-7]. The good resolution of the experiment permitted to detect C V, C VI and O VII lines. In this paper we intend to compare results obtained during these two flights and discuss temperature and abundance determinations from the X-ray spectroscopic measurements already available. In particular the Solid State Spectrometer results are compared with those obtained by a Japanese Group using a Gas Scintillation Proportional Counter [3].

The measurement and interpretation of Ne VII spectral line intensity ratios

Results are presented for the measurement, using the branching ratios calibration method, of the spectral intensities of Ne VII lines emitted from a theta -pinch plasma whose electron temperature and density have been found by laser scattering and other methods. Taking the principal resonance line as the reference line, the comparisons of predicted and measured line ratios show good agreement for lines with upper terms 2s3s 1S, 2s3d 1D, 2s3d 3S, 2s3p 3P, 2s3d 3D and 2p3s 3P. The theoretical excitation rate coefficient from 2s2 1S to 2s3p 1P, X(2s2 1S, 2s3p 1P), appears about a factor two too low. For the 2s2p 3P-2p2 3P line, the theoretical ratio is slightly higher than the experimental ratio while for 2s2p 1P-2p2 1D the average experimental ratio is 58% of the theoretical one. An experimental upper limit for X(2s2p 1P-2p2 1D) was deduced for two different plasma conditions. One of the results was consistent with theory. For the intercombination line ratio and for X(2s2p 3P, 2p2 3P), X(2s2p 3P, 2s3d 3D) and X(2s2p 3P, 2p3s 3P) evaluated from ratios involving the intercombination line, there is about a factor three between theory and experiment. A reduction in the intercombination line intensity because the calibration line C III 2p2 1D-2s3p 1P A value is too high by a factor of three would reconcile this. In Ne VII the theoretical A value of 2p2 3P-2s3p 3P is a factor of six higher than the experimental value.