相关论文: Interpreting the Hydrogen IR Lines - Impact of Imp…

Neutral sodium is a minority species in the atmospheres of late-type stars, and line formation in local thermodynamic equilibrium (LTE) is often a poor assumption, in particular for strong lines. We present an extensive grid of non-LTE…

Aims. We investigate the effect of the electric return currents in solar flares on the profiles of hydrogen Balmer lines. We consider the monoenergetic approximation for the primary beam and runaway model of the neutralizing return current.…

The broadening of the hydrogen lines during flares is thought to result from increased charge (electron, proton) density in the flare chromosphere. However, disagreements between theory and modeling prescriptions have precluded an accurate…

The near-IR HeI 10830A transition is a highly sensitive diagnostic for non-LTE effects in the helium atom. So far, non-LTE line-formation computations have failed to quantitatively reproduce observations of this line in the entire range of…

Stellar parameters and abundances of Na, Mg, Al, K, Ca, Sr, Ba, and Eu are determined for four very metal-poor stars (-2.66 < [Fe/H] < -2.15) based on non-LTE line formation and analysis of high-resolution (R ~60000 and 90000) high…

Quantitative analyses of low-mass hydrogen-deficient (super-)giant stars - so-called extreme helium stars - to date face two major difficulties. First, theory fails to reproduce the observed helium lines in their entirety, wings and line…

We present new observations of the center-to-limb variation of spectral lines in the quiet Sun. Our long-slit spectra are corrected for scattered light, which amounts to 4-8 % of the continuum intensity, by comparison with a Fourier…

The influence of inelastic hydrogen atom collisions on non-LTE spectral line formation has been, and remains to be, a significant source of uncertainty for stellar abundance analyses, due to the difficulty in obtaining accurate data for…

We present theoretical calculations of the quasi-molecular line profiles for the Lyman (Lya, Lyb, Lyg, Lyd) and Balmer (Ha, Hb, Hg, Hd, He, H8, H9, and H10) series, perturbed by collisions with protons. In all calculations we include the…

We investigated the reliability of our silicon atomic model and the influence of non-local thermodynamical equilibrium (NLTE) on the formation of neutral silicon (Si I) lines in the near-infrared (near-IR) H-band. We derived the…

Iron plays a crucial role in studies of late-type stars. In their atmospheres, Fe I is the minority species and its lines are subject to the departures from LTE. In contrast, one believes that LTE is a realistic approximation for Fe II…

As one of the most important elements in astronomy, iron abundance determinations need to be as accurate as possible. We investigate the accuracy of spectroscopic iron abundance analyses using archetypal metal-poor stars. We perform…

Hydrogen recombination lines are one of the major diagnostics of H II region physical properties and kinematics. In the near future, the Expanded Very Large Array (EVLA) and the Atacama Large Millimeter Array (ALMA) will allow observers to…

We present new calculations of unified line profiles for hydrogen perturbed by collisions with protons. We report on new calculations of the potential energies and dipole moments which allow the evaluation of profiles for the lines of the…

There is observational evidence showing that stellar and solar flares occur in a similar circumstance, although the former are usually much more energetic. It is expected that the bombardment by high energy electrons is one of the chief…

We present a detailed study of the non-Local Thermodynamic Equilibrium (non-LTE) formation of the high-excitation neutral oxygen 777 nm triplet in MARCS model atmospheres representative of late-type stars with spectral types F to K. We…

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…

A comprehensive model atom for Fe with more than 3000 energy levels is presented. As a test and first application of this model atom, Fe abundances are determined for the Sun and five stars with well determined stellar parameters and…

Accurate atomic data have become available in the recent past due to the demands of astrophysics and fusion research. We report on the impact of such data on non-LTE line-formation calculations for CNO in early-type stars. Considerable…

Stark broadened lines of the hydrogen Brackett series are computed for the conditions of stellar atmospheres and circumstellar envelopes. The computation is performed within the Model Microfield Method, which includes the ion dynamic…