On the Pulsation in the Atmosphere of η Aquilae.

Abstract

On twenty spectra of ~ Aquilae, taken with the coudé spectrograph of the 100-inch telescope with a dispersion of 2.9 A/mm and covering the entire pulsation cycle, forty-three lines of iron were selected for measurement. The radial-velocity variations of these lines were found to indicate that the selected lines of Fe i and Fe ii arise essentially from the same atmospheric layers. From the depth measurements of these lines the variations of the excitation temperature and of the electron pressure were determined. The equivalent widths, determined for a few iron lines at mid-descending branch, showed that the hydrogen-metal ratio in ~ Aquilae can differ from that in the sun by only a small factor. The curve of growth at the same phase gave turbulent velocities much smaller than the velocities determined from line profiles, which may possibly indicate the existence of a fast turbulence with very large elements. From the above data the density variation was computed. The comparison of this variation with that of the velocity suggests that possibly in the atmosphere of ~ Aquilae the kinetic temperature in- creases greatly with height and that in the highest layers the pulsation has the character of a simple pro- gressive wave. I. INTRODUCTIO