Non-LTE analysis of the ultraviolet spectrum of A type stars. II Theoretical considerations and interpretation of the VEGA Lyman-alpha region

Details Non-LTE analysis of the ultraviolet spectrum of A type stars. II Theoretical considerations and interpretation of the VEGA Lyman-alpha region Non-LTE analysis of the ultraviolet spectrum of A type stars. II Theoretical considerations and interpretation of the VEGA Lyman-alpha region

May 1981

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1981a%26a....98...96h&link_type=abstract

Astronomy and Astrophysics, vol. 98, no. 1, May 1981, p. 96-111.

Astronomy and Astrophysics

Astronomy

38

A Stars, Main Sequence Stars, Stellar Atmospheres, Ultraviolet Astronomy, Atmospheric Models, Line Spectra, Lyman Alpha Radiation, Nonequilibrium Thermodynamics

Scientific paper

Main-sequence early A-type model stellar atmospheres are investigated. The intention is to clarify the interpretational significance of the various assumptions used in calculating model stellar atmospheres and the emergent radiative flux. Several non-LTE model atmospheres in radiative and hydrostatic equilibria for early A-type stars are constructed. The effects of departures from LTE for early A-type stars are found to be of primary importance for the far ultraviolet spectrum and significant in the ultraviolet spectrum. It is also found that the properties of the computed NLTE model atmospheres are sensitive to the assumptions of the treatment of the far ultraviolet opacity sources. A qualitative estimate reveals that the run of physical parameters of a realistic NLTE line-blanketed model atmosphere is bracketed by that of the NLTE model without line-blanketing from the one side and that of the LTE line-blanketed model from the other side. It is noted that at present there does not exist any theoretical model yielding a 'correct' ultraviolet flux, particularly that below 1520 A for A stars.

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