Abstract We present laboratory measurements of n = 3 → n = 1 N v X-ray emission lines situated near 26 Å. The lines are excited by electron-impact collisions and are shown to reach a combined ...intensity of about a fifth of the combined strong N v 1 s 2 s 2 p 2 P 1/2,3/2 → 1 s 2 2 s 2 S 1/2 resonance lines, commonly labeled q and r , at 29.4 Å. In addition, we present new experimental data for the wavelength of the blended q and r lines at 29.4 Å, as well as for that of the blended inner-shell-excited N v lines u and v at 30.0 Å. All of these collisional N v lines need to be included in astrophysical emission models in order to properly account for flux from N v in the soft X-ray region. The measured wavelengths provide benchmarks for testing atomic structure calculations and excellent agreement is found with our calculations using the many-body perturbation theory method. We provide a complete listing of the N v energy levels with valence electrons in the n = 2, 3, and 4 shells calculated with this approach. The experimental and theoretical data, thus, provide accurate rest-frame wavelengths needed for velocity determinations based on high-resolution absorption features in spectra of warm absorbers in active galactic nuclei and other astrophysical objects.
Abstract
We report on emission spectra of iron in the extreme ultraviolet recorded at an electron density of ∼10
11
cm
−3
on the Lawrence Livermore electron beam ion trap facility. We present a ...summary of the observed emission lines, including wavelengths and emission intensities, and present spectra of pure Fe
xiv
through Fe
xvi
emission derived from our measurements in the 40–100 Å wavelength range. We show that spectral models, especially the current version of CHIANTI v10.0, describe the M-shell emission from these three charge states of iron reasonably well, and we are able to verify several transitions in CHIANTI for the first time.
The newly commissioned Orion laser system has been used to study dense plasmas created by a combination of short pulse laser heating and compression by laser driven shocks. Thus the plasma density ...was systematically varied between 1 and 10 g/cc by using aluminum samples buried in plastic foils or diamond sheets. The aluminum was heated to electron temperatures between 500 and 700 eV allowing the plasma conditions to be diagnosed by K-shell emission spectroscopy. The K-shell spectra show the effect of the ionization potential depression as a function of density. The data are compared to simulated spectra which account for the change in the ionization potential by the commonly used Stewart and Pyatt prescription and an alternative due to Ecker and Kröll suggested by recent x-ray free-electron laser experiments. The experimental data are in closer agreement with simulations using the model of Stewart and Pyatt.
The coronal temperature of Capella and Procyon has been derived from the spectral emission of Fe XVII observed in high resolution with Chandra's High Energy Transmission Grating Spectrometer. The ...measurement makes use of well resolved dielectronic satellite features with a spectator electron in the n = 4 shell. This method does not require a priori knowledge of the ionization equilibrium or of the elemental abundances. We find the temperature of Fe XVII emission is eV for Procyon and eV for Capella, i.e., 3.1 and 6.0 MK, respectively. The Procyon measurement is based on three X-rays observed in the dielectronic satellite feature, which illustrates the power of the method even for low-signal observations.
Detailed angle and energy resolved measurements of positrons ejected from the back of a gold target that was irradiated with an intense picosecond duration laser pulse reveal that the positrons are ...ejected in a collimated relativistic jet. The laser-positron energy conversion efficiency is ∼2×10{-4}. The jets have ∼20 degree angular divergence and the energy distributions are quasimonoenergetic with energy of 4 to 20 MeV and a beam temperature of ∼1 MeV. The sheath electric field on the surface of the target is shown to determine the positron energy. The positron angular and energy distribution is controlled by varying the sheath field, through the laser conditions and target geometry.
Laboratory measurements of the n = 3 to n = 3 emission from M-shell iron ions are presented and compared to synthetic spectra from the CHIANTI spectral model. The measurements cover the range 170-290 ...Angstrom and are made at an electron density of about 10 super(11) cm super(3-). Emission from Fe VIII through Fe XVI has been identified. Excellent agreement with CHIANTI predictions is found for most lines. Twenty weaker features are noted in the laboratory data that are either absent in CHIANTI or have recently been added and correspond to lines that have not been verified by experimental measurements. A few of these lines may have already been observed (but not yet identified) in the Sun. The features are attributed to emission from various charge states of iron, notably Fe IX and Fe XIII, and two features have been identified as transitions in Fe VIII, i.e., the 3p super(6)3d super(2)D sub(5/2)-3p super(5)3d super(2) super(2)P sub(3/2) and the 3p super(6)3d super(2)D sub(3/2)-3p super(5)3d super(2) super(2)P sub(1/2) transitions at 225.25 + or - 0.12 and 226.35 + or - 0.10 Angstrom, respectively. Seven lines in Fe XI, Fe XII, and Fe XIII between 200 and 205 Angstrom are noted for which the wavelengths in the CHIANTI database disagree with those in the current database of the National Institute of Standards and Technology. Our measurements of five of these lines appear to agree with the assignments used in CHIANTI.
We present electron-density-sensitive line ratios for Fe xiii- xvi measured in the spectral wavelength range of 200-440 and an electron density range of (1-4) × 1013 cm−3. The results provide a test ...at the high-density limit of density-sensitive line ratios useful for astrophysical studies. The measurements were performed on the National Spherical Torus Experiment-Upgrade, where electron densities were measured independently by the laser Thomson scattering diagnostic. Spectra were collected with a flat-field grazing-incidence spectrometer, which provided a spectral resolution of up to 0.3 , i.e., high resolution across the broad wavelength range. The response of the instrument was relatively calibrated using spectroscopic techniques in order to improve accuracy. The line ratios are compared to other laboratory sources and the latest version of CHIANTI (8.0.2), and an agreement within 30% is found.
We measured the L-shell emission spectrum of Fe xvii in a low-density, low-gradient magnetically confined laboratory plasma that contains predominately C, O, Fe, and Ni as trace elements and found ...excellent agreement with the relative spectral emission obtained in solar and astrophysical observations. However, we obtained spectra that appear to have an usually large Fe xvii resonance transition, which is commonly labeled , from hot plasmas that also contain fluorine. The wavelength of the Ly feature of F ix is coincident with the wavelength of the Fe xvii line within one part in 538, and its flux, therefore, enhances the Fe xvii resonance line. Moreover, the resonance and forbidden lines of F viii are close to the transitions in Fe xvii and may further alter the inferred apparent Fe xvii line ratios, particularly in spectrometers with moderate spectral resolution. The enhanced emission of line can thus serve as a new spectral diagnostic for the detection of fluorine in astrophysical plasmas.
Dielectronic recombination satellite emission to the Fe XVIII and Fe XIX L-shell spectra have been investigated using collisional-radiative modeling of X-ray transitions near 14 Angstrom. Although ...weak, such L-shell emission may be of interest for future temperature measurements of cool stars. The diagnostic has been evaluated using X-ray data from the Capella system measured by the Chandra X-Ray Observatory.
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