The Stark Effect of the Higher Balmer Lines in Stars of Spectral Types a and B.

Abstract

view Abstract Citations (15) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Stark Effect of the Higher Balmer Lines in Stars of Spectral Types a and B. van Dien, Elsa Abstract The purpose of the investigation was to compute the number of Balmer lines which should be visible in a stellar spectrum on the following assumptions: (1) the stellar atmosphere consists of hydrogen oniy; (2) the static Stark effect is the only agent of line broadening; (3) the stellar atmosphere is uniformly stratified in gravitational equilibrium. For the probability distribution of the field strength in an ionized gas, Holtsmark's theoretical results were used, as modified by Verweij. For the Stark pattern of the higher Balmer lines a simplifying assump- tion was introduced, suggested by Pannekoek. Eddington's equations of radiative transfer were inte- grated numerically for a number of wave lengths between 3660 A and 3750 A and for the following at- mospheres: surface temperatures 10,0800, 12,600°, 16,800°, and at each temperature surface gravities 102, 1O~, 106, 108. The values of the coefficient of continuous absorption for hydrogen were taken from published computations by Pannekoek. The theoretical results were compared with three groups of observational data: bright stars, eclipsing binaries, and two white dwarfs. The white dwarfs seem to conform to the theoretical expectations; but here the data on mass, radius, and temperature are more uncertain than for the two other classes of objects. It was found that in a large number of stars of the first two groups more hydrogen lines can be observed than are predicted by theory. In many of these stars the effective surface gravity seems to be only one one-hundredth of the dynamical value, or less. This agrees with results of Schalé and of Pannekoek and Reesinck. Several possibilities are investigated which might account for the discrepancy found. Radiation pres- sure and electron scattering may, in a few cases, have some effect but not to an extent sufficient to explain all the disagreement. In the temperature range considered, the absorption by negative hydrogen ions is negligible. It is suggested that stellar atmospheres are not built according to the model, which assumes equilibrium and stratification under the influence of gravitation and radiation pressure Publication: The Astrophysical Journal Pub Date: May 1949 DOI: 10.1086/145150 Bibcode: 1949ApJ...109..452V full text sources ADS |