Electron Collisional Broadening of Isolated Lines from Multiply-Ionized Atoms

Recent experimental and theoretical (both improved semiclassical and fully quantum-mechanical) results for B III and Ne VII delta n = 0 transitions with n = 2 or 3, respectively, are discussed. The probable reasons for disagreements by about a factor of 2 between the fully quantum-mechanically calculated and both measured and semiclassically calculated widths can be explained in terms of violation of validity criteria and non-thermal Doppler effects. More independent determinations of line widths for multiply-ionized non-hydrogenic ions are called for, but meanwhile caution should be exercised in the use of corresponding semiclassically calculated widths, e.g., in opacity calculations or for plasma density diagnostics. Only the quantum calculations allow a clear separation of elastic and inelastic scattering contributions to the width. For B III, elastic scattering contributes about 30% whereas for Ne VII inelastic scattering dominates. This allows rather direct comparisons with benchmark electron-ion scattering experiments.Comment: 13 pages, PostScript only. To appear in JQSR

Corrections to the Asymptotic Holtsmark Formula for Hydrogen Lines Broadened by Electrons and Ions in a Plasma

Corrections to asymptotic Holtsmark formula for hydrogen lines broadened by electrons and ions in plasm

Electron Impact Broadening of Isolated Ion Lines

Electron impact broadening of isolated ion spectral line

Electron-impact broadening of the 3s-3p lines in low-Z Li-like ions

The collisional electron-impact line widths of the 3s-3p transitions in Li-like ions from B III to Ne VIII are calculated with the convergent close-coupling (CCC) method from the atomic collision theory. The elastic and inelastic contributions to the line broadening and their Z-scaling are discussed in detail, and comparisons with recent experimental and theoretical results are also presented. It is found that similar to our previous study of line broadening in Be-like ions, the difference between experimental and CCC results monotonically increases with the spectroscopic charge of an ion.Comment: 23 pages, 8 figures, 1 table. To be published in JQSR

Study of a colliding laser-produced plasma by analysis of time and space-resolved image spectra

The interaction of two counter-propagating laser-produced plasmas was studied using simultaneous imaging and spectroscopic techniques. Spectrally-filtered time-gated ICCD imaging was used to obtain information about the spatial dynamics and temporal evolution of the collision process. While, time-resolved imaging spectroscopy was used to determine the spatial and temporal distributions of electron temperature and density within the interaction region. We examine specifically the interaction of plasmas whose parameters match those typically used in pulsed laser deposition of thin films. These low temperature plasmas are highly collisional leading to the creation of a pronounced stagnation layer in the interaction region

Experimental and theoretical investigation of plasma radiation Semiannual status report, Sep. 1969 - Feb. 1970

Stark broadening of argon and neon resonance line

New parametrization for differences between plasma kinetic codes

Validation and verification of plasma kinetics codes requires the development of quantitative methods and techniques for code comparisons. We describe two parameters that can be used for characterization of differences between such codes. It is shown that these parameters, which are determined from the most general results of kinetic codes, can provide important information on the differences between the basic rate coefficients employed. Application of this method is illustrated by comparisons of some results from the 3rd NLTE Code Comparison Workshop for carbon, germanium, and gold plasmas.Comment: Submitted to High Energy Density Physics, 12 pages, 2 figure

More on the Narrowing of Impact Broadened Radio Recombination Lines at High Principal Quantum Number

Recently Alexander and Gulyaev have suggested that the apparent decrease in impact broadening of radio recombination lines seen at high principal quantum number n may be a product of the data reduction process, possibly resulting from the presence of noise on the telescope spectra that is not present on the calculated comparison spectra. This is an interesting proposal. However, there are serious problems with their analysis that need to be pointed out. Perhaps the most important of these is the fact that for principal quantum numbers below n = 200, where the widths are not in question, their processed generated profile widths do not fit the widths of the processed lines obtained at the telescope. After processing, the halfwidths of the generated and telescope profiles must agree below n = 200 if we are to believe that the processed generated linewidths above n = 200 are meaningful. Theirs do not. Furthermore, we find that after applying the linewidth reduction factors found by Alexander and Gulyaev for their noise added profiles to our generated profiles to simulate their noise adding effect, the processed widths we obtain still do not come close to explaining the narrowing seen in the telescope lines for n values in the range 200 < n < 250. It is concluded that what is needed to solve this mystery is a completely new approach using a different observing technique instead of simply a further manipulation of the frequency-switched data.Comment: Six pages with 4 figures. Accepted for publication in Astrophysics and Space Scienc

Accelerated Recombination due to Resonant Deexcitation of Metastable States

In a recombining plasma the metastable states are known to accumulate population thereby slowing down the recombination process. We show that an account of the doubly-excited autoionizing states, formed due to collisional recombination of metastable ions, results in a significant acceleration of recombination. A fully time-dependent collisional-radiative (CR) modeling for stripped ions of carbon recombining in a cold dense plasma demonstrates an order of magnitude faster recombination of He-like ions. The CR model used in calculations is discussed in detail.Comment: 15 pages, 4 figures; to be published in JQSR

Hydrogen and helium line formation in OB dwarfs and giants. A hybrid non-LTE approach

Aims: Hydrogen and helium line spectra are crucial diagnostic features for the quantitative analysis of OB stars. We compute synthetic spectra based on a hybrid non-LTE approach in order to test the ability of these models to reproduce high-resolution and high-S/N spectra of dwarf and giant stars and also to compare them with published grids of non-LTE (OSTAR2002) and LTE (Padova) models. Methods: Our approach solves the restricted non-LTE problem based on classical line-blanketed LTE model atmospheres. State-of-the-art model atoms and line-broadening theories are employed to model the H and He I/II spectra over the entire optical range and in the near-IR. Results: The synthetic spectra match almost all measurable hydrogen and helium lines observed in six test stars over a wide spectral range from the Balmer limit to the NIR, except for only a few well-understood cases. Our approach reproduces other published non-LTE calculations, however avoids inconsistencies with the modelling of the He I singlets recently discussed in the literature. It improves on the published LTE models in many aspects: non-LTE strengthening and the use of improved line-broadening data result in overall significant differences in the line profiles and equivalent widths of the Balmer and helium lines. Where possible, systematic effects on the stellar parameter determination are quantified, e.g. gravities derived from the Hgamma wings may be overestimated by up to ~0.2 dex at our upper temperature boundary in LTE. (abridged)Comment: 25 pages, 19 figures. Modified according to suggestions of the referee. Accepted for publication in A&A. Several figures in low resolution. A high-resolution pdf version of the preprint can be downloaded from http://www.sternwarte.uni-erlangen.de/~ai97/preprints/HHe_nieva.pd