A N Ryabtsev

EUV spectra of Gd and Tb ions excited in laser-produced and vacuum spark plasmas

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 A region and investigated on the basis of the Hartree–Fock calculations using Cowan code. The intense peaks in the 65–75 A region of the vacuum spark spectra were interpreted as a manifold of the 4d104fm–4d94fm+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 4d104fm–4d94fm+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 4p64dk (k=8–10) and 4d104fm (m=1–2) ground configuration ions predominantly excited in hotter laser-produced plasma. The most intense lines of the 4d104f2–4d104f5d transitions in the Gd XVII and Tb XVIII spectra were classified for the first time.

Rare-earth elements in the atmosphere of the magnetic chemically peculiar star HD 144897 , New classification of the Nd III spectrum

Context. The chemically peculiar stars of the upper main sequence represent a natural laboratory for the study of rare-earth elements (REE). Aims. We want to check the reliability of the energy levels and atomic line parameters for the second REE ions currently available in the literature, and obtained by means of experiments and theoretical calculations. Methods. We have obtained a UVES spectrum of a slowly rotating strongly magnetic Ap star, HD 144897, that exhibits very large overabundances of rare-earth elements. Here we present a detailed spectral analysis of this object, taking effects of non-uniform vertical distribution (stratification) of chemical elements into account. Results. We determined the photospheric abundances of 40 ions. For seven elements (Mg, Si, Ca, Ti, Cr, Mn, Fe), we obtained a stratification model that allows us to produce a satisfactory fit to the observed profiles of spectral lines of various strengths. All the stratified elements but Cr show a steep decrease in concentration toward the upper atmospheric layers; for Cr the transition from high to low concentration regions appears smoother than for the other elements. The REEs abundances, which have been determined for the first time from the lines of the first and second ions, have been found typically four dex higher than solar abundances. Our analysis of REE spectral lines provides strong support for the laboratory line classification and determination of the atomic parameters. The only remarkable exception is Nd iii, for which spectral synthesis was found to be inconsistent with the observations. We therefore performed a revision of the Nd iii classification. We confirmed the energies for 11 out of 24 odd energy levels that were classified previously, and derived the energies for additional 24 levels of Nd iii, thereby substantially increasing the number of classified Nd iii lines with corrected wavelengths and atomic parameters.

Non-LTE effects on the lead and thorium abundance determinations for cool stars

Context. Knowing accurate lead abundances of metal-poor stars provides constraints on the Pb production mechanisms in the early Galaxy. Accurately deriving thorium abundances permits a nucleo-chronometric age determination of the star. Aims. We aim to improve the calculation of the Pb i and Th ii lines in stellar atmospheres based on non-local thermodynamic equilibrium (non-LTE) line formation, and to evaluate the influence of departures from LTE on Pb and Th abundance determinations for a range of stellar parameters by varying the metallicity from the solar value down to [Fe/H] = −3. Methods. We present comprehensive model atoms for Pb i and Th ii and describe calculations of the Pb i energy levels and oscillator strengths. Results. The main non-LTE mechanism for Pb i is the ultraviolet overionization. We find that non-LTE leads to systematically depleted total absorption in the Pb i lines and accordingly, positive abundance corrections. The departures from LTE increase with decreasing metallicity. Using the semi-empirical model atmosphere HM74, we determine the lead non-LTE abundance for the Sun to be log ePb,� = 2.09, in agreement with the meteoritic lead abundance. We revised the Pb and Eu abundances of the two strongly r-process enhanced stars CS 31082-001 and HE 1523-0901 and the metal-poor stellar sample. Our new results provide strong evidence of universal Pb-to-Eu relative r-process yields during the course of Galactic evolution. The stars in the metallicity range −2.3 < [Fe/H] < −1.4 have Pb/Eu abundance ratios that are, on average, 0.51 dex higher than those of strongly r-process enhanced stars. We conclude that the s-process production of lead started as early as the time when Galactic metallicity had reached [Fe/H] = −2.3. The average Pb/Eu abundance ratio of the mildly metal-poor stars, with −1.4 ≤ [Fe/H] ≤− 0.59, is very close to the corresponding Solar System value, in line with the theoretical predictions that AGB stars with [Fe/H] �− 1 provided the largest contribution to the solar abundance of s-nuclei of lead. The departures from LTE for Th ii are caused by the pumping transitions from the levels with Eexc < 1 eV. Non-LTE leads to weakened Th ii lines and positive abundance corrections. Overall, the abundance correction does not exceed 0.2 dex when collisions with H i atoms are taken into account in statistical equilibrium calculations.

Analyses of the Sn IX?Sn XII spectra in the EUV region

The Sn IX–Sn XII spectra excited in a vacuum spark have been analysed in the 130–160 A wavelength region. The analysis was based on the energy parameter extrapolation in the isonuclear Sn VI–VIII and Sn XIII–XIV sequence. 266 spectral lines belonging to the 4dm–(4dm−14f+4p54dm+1) (m=6–3) transition arrays were classified in the Sn IX–Sn XII spectra for the first time. All 18 level energies of the 4d3 configuration and 39 level energies of the strongly interacting 4d24f and 4p54d4 configurations were established in the Sn XII spectrum. The energy differences between the majority of the 4dm levels and about 40 levels of the 4dm−14f+4p54dm+1 configurations were determined in each of the Sn IX, Sn X and Sn XI spectra (m=6–4). As a result, all intense lines were classified in the 130–140 A region relevant to the extreme ultraviolet (EUV) lithography. It was shown that the most of the intense lines in the 2% bandwidth at 135 A belong to the transitions in the Sn XI–Sn XIII spectra.

Identification of n = 4, ?n = 0 transitions in the spectra of nickel-like and zinc-like ions through tin

Spectra of multicharged ions have been analyzed for all stable elements in the period from Z = 37 (Rb) to Z = 50 (Sn), in the region of n = 4, Δn = 0 transitions. The transition arrays (4s2 + 4p2 + 4s4d)-4s4p, 4s4f and 3d94s, 3d94d-3d94p have been identified in zinc-like and nickel-like ions respectively, with the help of the ab initio relativistic parametric potential method and of the Slater-Condon method with generalized least-squares fits of energy parameters.

A Detailed Analysis of the n=3 – n'=3 Transitions in the Mg-like Ions FeXV, CoXVI and NiXVII

Laser produced spectra of iron, cobalt and nickel were obtained using the 6.65 m normal incidence vacuum spectrograph with a short-wave blazed 1200 lines/mm grating. Transitions between the configurations 3s2, 3s3p, 3p2, 3s3d and 3p3d of the Mg-like ions FeXV, CoXVI and NiXVII were studied in the region 170-600 A. Singlet-triplet connections were found for these ions. The previous identifications were revised and 60 new lines, mainly from the 3p3d configuration, were found. Wavelengths were remeasured and related energy levels were improved. New identifications of solar flare lines are proposed on the basis of this work.

Non-LTE line formation for Pr ii and Pr iii in A and Ap stars

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 Teff ≥ 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 τ5000 < −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.

Analysis of the spectrum of the (5d5+5d46s)-(5d46p+5d36s6p) system of triply ionized osmium (Os IV)

The spectrum of osmium was photographed in the 225–2100A region on a 3-m normal incidence spectrograph using a triggered spark light source and on a 10-m normal incidence spectrograph using a sliding spark source. The (5d5+5d46s)–(5d46p+5d36s6p) transition arrays of Os IV were investigated and 934 lines were classified between and The 705A and 1995A. The analysis has resulted in the determination of 61 levels in the (5d5+5d46s) even system and of 124 levels in the 5d46p configuration. Five levels of the 5d36s6p configuration were also identified. The energy levels and their eigenvector compositions have been described by means of the orthogonal operator technique. The 2-particle magnetic operators of the dp-type are compared with values obtained in other spectra. Accurate weighted transition probabilities (gA-values) calculated by means of orthogonal operators are also presented.

Analysis of the spectrum of the (5d4 + 5d36s)−5d36p system of four times ionized osmium (Os V)

The spectrum of osmium was photographed in the 225-2100 A region on a 3m normal incidence spectrograph using a triggered spark light source. The (5d4 + 5d36s)−5d36p transition arrays of Os V were investigated and 703 lines have been classified. The analysis of the spectrum of Os V has resulted in the determination of 57 levels in the (5d4 + 5d36s) even system and of 89 levels in the 5d36p odd level system. The energy levels and their eigenvector compositions have been described by means of the orthogonal operator technique. Three particle electrostatic effects of the ddp-type have been established for the first time in the 5d-elements. Accurate gA-values calculated by means of orthogonal operators are presented also.

Analysis of the spectrum of five times ionized osmium (Os VI)

The analysis of Os VI has for the even system resulted in the determination of all levels (19) in the 5d3 ground configuration and of 14 levels out of 16 theoretically possible levles in the 5d26s configuration. In the odd system all levels (45) of the 5d26p configuration have been found. In the 435-765 A wavelength region 290 lines belonging to the 5d3-5d26p transition array have been classified, while in the 940-1510 A wavelength region 87 lines belonging to the 5d26s-5d26p transition array were classified. The analysis was guided by predicted energy level values and transition probabilities calculated by means of a complete set of orthogonal operators. Calculated energy values, LS-compositions and gA-values, obtained from the final fitted parameter values using the orthogonal operator approach are given.