NLTE model stellar atmospheres with line blanketing near the series limits

Details NLTE model stellar atmospheres with line blanketing near the series limits NLTE model stellar atmospheres with line blanketing near the series limits

Feb 1994

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994a%26a...282..151h&link_type=abstract

Astronomy and Astrophysics (ISSN 0004-6361), vol. 282, no. 1, p. 151-167

Astronomy and Astrophysics

Astrophysics

109

Atmospheric Models, Balmer Series, Rydberg Series, Stellar Atmospheres, Stellar Models, Stellar Spectrophotometry, Stellar Temperature, Thermodynamic Equilibrium, Atmospheric Temperature, Computerized Simulation, Formalism, Mathematical Models, Stellar Spectra

Scientific paper

In this paper we study the influence of line-merging regions at the intermediate long-wavelength side of a continuum threshold on the computed model atmosphere structure and predicted spectrum. In order to model these regions sufficiently accurately, we have developed two concepts. First, we have extended the occupation probability formalism of Hummer and Mihalas to non-local thermodynamic equilibrium (non-LTE) plasmas. Second, in order to treat the very complicated opacity in the line merging region, we have generalized the concept of opacity distribution functions to treat non-LTE situations. All Rydberg states are consistently included within this framework, so that no arbitrary cutoff of high (LTE) levels is made. We have calculated several pure hydrogen models atmospheres for two effective temperatures, Teff = 20000 and 35000 K, and discussed the differences between models calculated with various treatments of the line merging. In particular, we have shown that the error in the predicted profiles of Balmer lines resulting from the neglect of line merging is typically of the order of 3-4%, while the errors in the far-UV portion of the Balmer continuum reaches 15-35%. The errors generally decrease with increasing effective temperature. At the same time, the internal accuracy of the models is shown to be about or below 0.5% for all predicted spectral features. We conclude that for interpreting current high-accuracy spectrophotometric observations models including the line merging are necessary, and that the formalism developed in this paper is capable of providing a sufficiently accurate and robust modeling technique.

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