view Abstract Citations References Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Spectrophotometry of early A-type stars. Buscombe, William Abstract Coude' spectra of the main sequence star Gem norum and of the supergiant a Cygni in the wave-length region 3300-4700A have been traced with the new direct-intensity microphotometer at Mount Wilson Observatory. Empirical line-absorption coefficients, derived by other workers from the spectra of stars of both higher and lower excitation temperatures, were used to construct separate curves of growth for the regions on either side of the Balmer continuum. In the ultraviolet, Greenstein's unpublished provisional values of log o for the hydrogen-poor supergiant v Sagittarii were supplemented by a few laboratory line strengths for T ii, adjusted to that star's assumed temperature of 15,0000K. In the visible region, other semi-empirical line strengths from the solar curve of growth and from the metallic-line A star T Ursae Majoris were adjusted for abundance and temperature and averaged with the v Sgr material. Analysed with the aid of Wrubel's theoretical curve of growth, the measures of some 400 lines on each of 3 plates for each of the A stars indicate that their excitation temperatures are close to Io,0000K. Empirical log flo values for the A stars are being derived. The opacity difference measured across the Balmer continuum corresponds to seeing about 15 times more atoms above the photosphere in the violet than in the far ultraviolet. This is completely accounted for by continuous H and H- absorption at the electron pressures indicated by the ionisation of iron. The ratio of these electron pressures is confirmed by counting the number of Stark-broadened lines in the Balmer series whose cores can be resolved from the confluence of their wings, although the Inglis-Teller formula is more nearly valid for spectrograms of lower dispersion. The very flat transitional portions of the curves of growth indicate a damping constant of at most one-third the classical value. No significant difference in turbulence is evident between the visible and ultraviolet regions, either from the curves of growth or from the line profiles, whose form is remarkably near Gaussian. The velocities have been corrected for thermal motion, 1.6 km$sec, and instrumental broadening, half-half-width 4.6 km/sec. Evidently considerable energy is transferred below the photosphere in eddies with a wave length exceeding the scale height. Star and Spectrum Gem Al V a Cyg A2 Ia Electron Pressure 12,000 bars 1000 bars Turbulent vel. (c.o.g.) 4+ 1 km/sec 13+2 km/sec Turbulent vel. (profile) 14+ 2 km/sec 29+2 km/sec Princeton University Observatory Princeton, N. J. Publication: The Astronomical Journal Pub Date: October 1950 DOI: 10.1086/106387 Bibcode: 1950AJ.....55..166B full text sources ADS | data products SIMBAD (5)