High-resolution spectroscopy for a study of galactic chemical evolution

В лекции описан вклад спектроскопии высокого разрешения в исследования химической эволюции галактик.This paper reviews a role of high-resolution spectroscopy in studies of galactic chemical evolution.Работа выполнена в рамках программы фундаментальных исследований РАН, подпрограмма «Астрофизические объекты как космические лаборатории»

Determination of non-LTE barium abundances in solar-type stars: A technique for non-LTE calculations

Detailed statistical-equilibrium calculations are performed for the Ba II ion to elucidate the influence of non-LTE effects on barium abundances in the atmospheres of stars with Teff = 5500-6500 K, log g = 4.0 and 4.5, and [Fe/H] from -2 to 0. The computed non-LTE abundance corrections depend on the initial barium abundance εBa. They reverse sign as [Ba/H] changes from 0 to -2. The corrections are at a minimum for the λ5853 line (from -0.07 to +0.016 dex) and at a maximum for the λ6141 and 6496 lines (from -0.20 to +0.14 dex). In addition, the uncertainties in εBa resulting from errors in Teff, log g, and microturbulence ξt, as well as from the use of different model atmospheres and inaccuracies in the line-broadening parameters, are estimated

A non-LTE study of neutral and singly-ionized calcium in late-type stars

Non-local thermodynamical equilibrium (NLTE) line formation for neutral and singly-ionized calcium is considered through a range of spectral types when the Ca abundance varies from the solar value down to [Ca/H] = -5. Departures from LTE significantly affect the profiles of Ca I lines over the whole range of stellar parameters considered. However, at [Ca/H] >= -2, NLTE abundance correction of individual lines may be small in absolute value due to the different influence of NLTE effects on line wings and the line core. At lower Ca abundances, NLTE leads to systematically depleted total absorption in the line and positive abundance corrections, exceeding +0.5 dex for Ca I 4226 at [Ca/H] = -4.9. In contrast, NLTE effects strengthen the Ca II lines and lead to negative abundance corrections. NLTE corrections are small, <= 0.02 dex, for the Ca II resonance lines. For the IR lines of multiplet 3d - 4p, they grow in absolute value with decreasing Ca abundance exceeding 0.4 dex in metal-poor stars with [Fe/H] <= -3. Ca abundances are determined for the Sun, Procyon, and seven metal-poor stars, using high S/N and high-resolution spectra at visual and near-IR wavelengths. Lines of Ca I and Ca II give consistent abundances for all objects (except Procyon) when collisions with hydrogen atoms are taken into account. The derived absolute solar Ca abundance (from Ca I and Ca II lines) is \eps{Ca,\odot} = 6.38+-0.01. For Procyon, the mean Ca abundance from Ca I lines is markedly subsolar, [Ca/H] = -0.14+-0.03. The W(Ca I 4226)/W(Ca II 8498) equivalent width ratio is predicted to be sensitive to surface gravity for extremely metal-poor stars, while this is not the case for the ratio involving the Ca II resonance line(s)

NLTE Strontium and Barium in metal poor red giant stars

We present atmospheric models of red giant stars of various metallicities, including extremely metal poor (XMP, [Fe/H]<-3.5) models, with many chemical species, including, significantly, the first two ionization stages of Strontium (Sr) and Barium (Ba), treated in Non-Local Thermodynamic Equilibrium (NLTE) with various degrees of realism. We conclude that 1) for all lines that are useful Sr and Ba abundance diagnostics the magnitude and sense of the computed NLTE effect on the predicted line strength is metallicity dependent, 2) the indirect NLTE effect of overlap between Ba and Sr transitions and transitions of other species that are also treated in NLTE non-negligibly enhances NLTE abundance corrections for some lines, 3) the indirect NLTE effect of NLTE opacity of other species on the equilibrium structure of the atmospheric model is not significant, 4) the computed NLTE line strengths differ negligibly if collisional b-b and b-f rates are an order of magnitude smaller or larger than those calculated with standard analytic formulae, and 5) the effect of NLTE upon the resonance line of Ba II at 4554.03 AA is independent of whether that line is treated with hyperfine splitting. As a result, the derivation of abundances of Ba and Sr for metal-poor red giant stars with LTE modeling that are in the literature should be treated with caution.Comment: 28 pages, 10 figures. Accepted for publication in April 2006 Astrophysical Journa