Atmospheres of early type stars.

Abstract

view Abstract Citations (1) References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Atmospheres of early type stars. Aller, Lawrence H. Abstract The importance of early type stars with absorption spectra lies on the one hand in that the stellar absorption coefficient should be predictable in detail from theory and on the other in that they provide clues to the abundances of the light elements, hydrogen, helium, carbon, nitrogen, oxygen, neon, etc., which are of interest in connection with the stellar energy generation problem. Mt. Wilson coude' plates of 3 supergiant and 3 main sequence B stars have been utilized to determine line profiles and equivalent widths. With the aid of exact f-values for hydrogen and approximate f-values for other light elements it has been possible to estimate the relative abundances of H, He, C, N, 0, Ne, Mg, Al, 81, P, and S, the electron density, the number of atoms above the photosphere, and the effective surface gravity. Uncertainties arise not only from our ignorance of the true f-values, the damping constants appropriate for the stronger lines, and possible "turbulence in supergiant atmospheres (more precisely the non-equality of kinetic and effective temperatures), but also from inaccuracies in the effective temperature. The relative proportions of C, N, 0, Mg, and SI appear to be in fair agreement with the results of Uns&ld for r Scorpii, and the writer for 10 Lacertae, but the ratio of hydrogen to oxygen may be greater in the dwarf stars. The lines of Neli have been measured in ~ Orionis with the result that neon appears to be about a fifth as abundant as oxygen. Supergiant atmospheres present perplexing problems. The kinetic temperatures of the atmospheres of E Canis Majoris and x2 Orionis appear to be larger than the effective temperatures but the curve of growth is not sufficiently precise to fix the values. The effective surface gravity of the latter star as determined from the electron pressure and mass above the photosphere is about 10-2 that estimated from the mass and radius of the star, in accordance with the results found by Miss van Dien. The line profiles suggest the broadening arises from the Doppler motion of the radiating atoms. The high central intensities of the strong absorption lines suggest that they are formed according to Milne's scheme of local thermodynamic equilibrium. The exact value of the central intensity will depend on the wave length, the ratio of the continuous absorption coefficient at the point in question to the mean absorption coefficient, KX7K, and the effective temperature Te. If ~x~~ is constant with optical depth we can use the tables by Chandrasekhar and Miss Breen to predict the central intensities. A model atmosphere has been computed for 10 Lacertae, and the choice of the value of KX7K for an optical depth of 0.65 yields a satisfactory agreement between the observed and predicted central intensities of H~, H~, H~, and HE. Since we have a satisfactory theory of the stellar absorption coefficient for the hotter stars and since f-values may be computed for the observable lines of the light elements, an investigation similar to that carried out by B. Stro~mgren for the sun would appear to be in order. It would appear desirable to concentrate on a few lines whose f-values can be determined accurately and compute theoretical profiles and total absorptions. Kirkwood Observalory, Indiana University, __________ Bloomington, Ind. * Of papers presented at the Seventy-seventh Meeting of the American Astronomical Society, Evanston, Illinois, Septemher 3-6, 1947. The first five are ahstracts of papers that constituted a symposium on Stellar Atmospheres. Publication: The Astronomical Journal Pub Date: February 1948 DOI: 10.1086/106060 Bibcode: 1948AJ.....53..105A full text sources ADS |