Atmospheric Pulsation of the Cepheid Variable v Aquilae

Abstract

A new method of analyzing variable radial velocity data by a systematic study of line displacements from different elements and at different levels of a star's atmosphere has been developed and applied. The usual method of selecting lines giving consistent displacements has masked an effect here tentatively called atmospheric pulsation. A difference in the velocities from the hydrogen and the helium lines in the star, B.D. + 56" 2617, led to the idea of isolating the velocities of high-level elements. Application was made in the case of x Aurigae by isolating the hydrogen lines and a systematic distribution of the hydrogen velocity residuals with respect to phase was found. Based upon the isolation of velocities at three levels in the star's atmosphere the method adapted to the problem of Cepheid variation was first applied by Mr. J. A. Aldrich in a study of S. Sagittae. The method is also applicable to long-period and irregular variables, to secular and periodic changes in peculiar spectra, and to other astrophysical problems.