Extreme UV spectra of the gadolinium and terbium ions excited in the laser-produced plasma and vacuum spark sources were recorded in the 40-120 Å region and investigated on the basis of the Hartree-Fock calculations using Cowan code. The intense peaks in the 65-75 Å region of the vacuum spark spectra were interpreted as a manifold of the 4d 10 4f m -4d 9 4f m+1 transitions in the ions with a partially filled 4f shell. The drastic narrowing of these peaks was observed in the spectra of the laser-produced plasma. It was explained by a change of the 4d 10 4f m -4d 9 4f m+1 (m > 2) transition arrays mostly contributing to the intensity of the peaks in the vacuum spark spectra for the 4-4 transitions in the simplest spectra of the 4p 6 4d k (k = 8-10) and 4d 10 4f m (m = 1-2) ground configuration ions predominantly excited in hotter laser-produced plasma. The most intense lines of the 4d 10 4f 2 -4d 10 4f5d transitions in the Gd XVII and Tb XVIII spectra were classified for the first time.

Tungsten spectra excited in the vacuum sparks of different setups and electric circuits were recorded on two high-resolution vacuum spectrographs. For the region 190-500 Å, a 10 m normal incidence spectrograph with a 3600 lines/mm grating was used in the Meudon Observatory. In the region below 350 Å, a set of spectra was produced using a 3 m grazing incidence spectrograph with a 3600 lines/mm grating in the Institute of Spectroscopy in Troitsk. A total of 187 lines in the region 160-271 Å were identified as transitions to the low-lying odd configurations 4f 13 5s 2 5p 6 and 4f 14 5s 2 5p 5 from the interacting excited even 4f 12 5s 2 5p 6 5d + 4f 13 5s 2 5p 5 (5d + 6s) + 4f 14 5s 2 5p 4 (5d + 6s) + 4f 14 5s5p 6 configurations. It was found that 4f 13 5s 2 5p 6 2 F 7/2 is the ground level of W VIII. The fine structure splitting and relative positions of the odd terms were established, and 98 levels of the excited even configurations were found.

Aims. Among the known Ap stars, HD 101065 is probably one of the most interesting objects, demonstrating very rich spectra of rareearth elements (REE). Strongly peculiar photometric parameters of this star can not be fully reproduced by any modern theoretical calculations, even those accounting for realistic chemistry of its atmosphere. In this study we investigate a role of missing REE line opacity and construct a self-consistent atmospheric model based on accurate abundance and chemical stratification analysis. Methods. We employed the LLmodels stellar model atmosphere code together with DDAFit and Synthmag software packages to derive homogeneous and stratified abundances for 52 chemical elements and to construct a self-consistent model of HD 101065 atmosphere. The opacity in REE lines is accounted for in details, by using up-to-date extensive theoretical calculations. Results. We show that REE elements play a key role in the radiative energy balance in the atmosphere of HD 101065, leading to the strong suppression of the Balmer jump and energy redistribution very different from that of normal stars. Introducing new line lists of REEs allowed us to reproduce, for the first time, spectral energy distribution of HD 101065 and achieve a better agreement between the unusually small observed Strömgren c 1 index and the model predictions. Using combined photometric and spectroscopic approaches and based on the iterative procedure of abundance and stratification analysis we find effective temperature of HD 101065 to be T eff = 6400 K.

Aims. Non-local thermodynamical equilibrium (non-LTE) line formation for singly-ionized and doubly-ionized praseodymium is considered for a range of effective temperatures between 7250 K and 9500 K. We evaluate the influence of departures from LTE on Pr abundance determinations and determine a distribution of the Pr abundance in the atmosphere of the roAp star HD 24 712 from a non-LTE analysis of the Pr ii and Pr iii lines. Methods. A comprehensive model atom for Pr ii/iii is presented based on the measured and the predicted energy levels, in total, 6708 levels of Pr ii and Pr iii and the ground state of Pr iv. Calculations of the Pr ii energy levels and oscillator strengths for the transitions in Pr ii and Pr iii are described.Results. The dependence of non-LTE effects on the atmospheric parameters is discussed. At T eff ≥ 8000 K, departures from LTE lead to the overionization of Pr ii and, therefore, to systematically depleted total absorption in the line and positive abundance corrections. At the lower temperatures, different lines of Pr ii may be either weakened or amplified depending on the line strength. The non-LTE effects strengthen the Pr iii lines and lead to negative abundance corrections. Non-LTE corrections grow with effective temperature for the Pr ii lines, and, in contrast, they decline for the Pr iii lines. The Pr ii/iii model atom is applied to determine the Pr abundance in the atmosphere of the roAp star HD 24 712 from the lines of two ionization stages. In the chemically uniform atmosphere with [Pr/H] = 3, the departures from LTE may explain only a small part (approximately 0.3 dex) of the difference between the LTE abundances derived from the Pr ii and Pr iii lines ( 2 dex). We find that the lines of both ionization stages are fitted for the vertical distribution of praseodymium, where the Pr enriched layer with [Pr/H] ≥ 4 exists in the outer atmosphere at log τ 5000 < −4. The departures from LTE for Pr ii/iii are strong in the stratified atmosphere and have the opposite sign for the Pr ii and Pr iii lines. The praseodymium stratification analysis of roAp stars has to be performed based on non-LTE line formation. Using the revised partition function of Pr ii and experimental transition probabilities, we determine the solar non-LTE abundance to be log (Pr/H) = −11.15 ± 0.08.

The spectrum of ten times ionized xenon, Xe XI, was observed in the region 105–157 Å with a low-inductance vacuum spark and a 10.7 m grazing-incidence spectrograph. About 200 lines belonging to the 4d8–(4d75p + 4d74f + 4p54d9) transition array were observed. 140 of these lines are in the region 130–140 Å, which is of importance for extreme ultraviolet (EUV) lithography. The spectrum was interpreted by means of Hartree–Fock calculations and orthogonal parameters using scaling factors for the energy parameters obtained by extrapolation along the Rh II isoelectronic sequence. All 9 levels of the 4d8 configuration and 123 levels of the 4d75p + 4d74f + 4p54d9 configurations were established. Transition probabilities for all observed lines were calculated with fitted values of the energy parameters. A value of 1847200 ± 1600 cm-1 (229.02 ±0.20 eV) was obtained for the ionization energy.