Influence of inelastic collisions with hydrogen atoms on the non-LTE modelling of Ca I and Ca II lines in late-type stars

We perform the non-local thermodynamic equilibrium (NLTE) calculations for Ca I-II with the updated model atom that includes new quantum-mechanical rate coefficients for Ca I + H I collisions from two recent studies, that is, by Barklem and by Mitrushchenkov, Guitou, Belyaev, Yakovleva, Spielfiedel, and Feautrier, and investigate the accuracy of calcium abundance determinations using the Sun, Procyon, and five metal-poor (MP) stars with well-determined stellar parameters. We show that both collisional recipes lead to very similar NLTE results. When using the subordinate lines of Ca I and the high-excitation lines of Ca II, NLTE provides the smaller line-to-line scatter compared with the LTE case for each star. For Procyon, NLTE removes a steep trend with line strength among strong Ca I lines seen in LTE and leads to consistent [Ca/H] abundances from the two ionisation stages. In the MP stars, the NLTE abundance from Ca II 8498 A agrees well with that from the Ca I subordinate lines. NLTE largely removes abundance discrepancies between the high-excitation lines of Ca I and Ca II 8498 A obtained for our four [Fe/H] < -2 stars under the LTE assumption. We investigate the formation of the Ca I resonance line in the [Fe/H] < -2 stars. Consistent NLTE abundances from the Ca I resonance line and the Ca II lines are found for two hyper metal-poor stars HE0107-5240 and HE1327-2326. We provide the NLTE abundance corrections for 28 lines of Ca I in a grid of model atmospheres suitable for abundance analysis of FGK-type dwarfs and subgiants.Comment: 12 pages, 3 tables, 10 figures; accepted for publication in A&

Fusion reactions in molecules via nuclear threshold resonances

It is widely accepted that in molecular systems the nuclear interaction plays a negligible role, because of the strong Coulomb repulsion of the nuclei at small distances. We are going to show that this is not always true. The existence of an extended nuclear resonance may lead to considerably enhanced nuclear reaction rates in appropriately prepared molecules. Especially we point out that p+p+ ^{16}O, i.e., the constituents of water, can form a ^{18}Ne(1^-) threshold resonance which decays under energy release into ^{17}F and a proton.Comment: RevTeX, 9.4 Kb; Published version of the pape

Statistical Analysis of Precipitation Events

In the present paper we demonstrate the results of a statistical analysis of some characteristics of precipitation events and propose a kind of a theoretical explanation of the proposed models in terms of mixed Poisson and mixed exponential distributions based on the information-theoretical entropy reasoning. The proposed models can be also treated as the result of following the popular Bayesian approach.Comment: 5 pages, 4 figures; ICNAAM 201

Magnetic Moments of Heavy ΞQ\Xi_{Q} Baryons in Light Cone QCD Sum Rules

The magnetic moments of heavy $\Xi_{Q}$ baryons containing a single charm or bottom quark are calculated in the framework of light cone QCD sum rules method. A comparison of our results with the predictions of the quark models is presented.Comment: 26 Pages, 8 Figures and 1 Tabl

Perturbation of a lattice spectral band by a nearby resonance

A soluble model of weakly coupled "molecular" and "nuclear" Hamiltonians is studied in order to exhibit explicitly the mechanism leading to the enhancement of fusion probability in case of a narrow near-threshold nuclear resonance. We, further, consider molecular cells of this type being arranged in lattice structures. It is shown that if the real part of the narrow nuclear resonance lies within the molecular band generated by the intercellular interaction, an enhancement, proportional to the inverse width of the nuclear resonance, is to be expected.Comment: RevTeX, 2 figures within the file. In May 2000 the title changed and some minor corrections have been don