Astronomy and Astrophysics – Astronomy
Scientific paper
May 2000
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2000astl...26..309s&link_type=abstract
Astronomy Letters, vol. 26, p. 309-318 (2000)
Astronomy and Astrophysics
Astronomy
4
Scientific paper
The formation of NaI lines in X-ray illuminated atmospheres is investigated by abandoning the assumption of local thermodynamic equilibrium (LTE). Calculations are performed on the basis of a 21-level NaI model atom for the LTE model atmospheres of irradiated F-G stars obtained with allowance for a reflection effect in the first approximation. The state of extreme "overrecombination" is shown to exist for the populations of all NaI levels in the case of external illumination. Absorption features in the profiles of "cool" and "normal" NaI lines have been found to be enhanced compared to the LTE approximation. Effects of the angle of incidence and intensity of the external radiation on the formation of level populations and line profiles when abandoning LTE are analyzed. The existence of overrecombination for NaI is explained by the small X-ray heating function and the large optical cooling function. NaI level populations are shown to depend weakly on the presence of "overionization" for NaII in the atmospheres of irradiated stars.
Sakhibullin N. A.
Shimansky V. V.
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