A Comparison of the Near-Infrared and Visible Spectra of Three Bright Cepheids

摘要

Recent studies have suggested that significant differences may exist between the IR and the visible radial velocity curves and line profiles for Cepheid variable stars. Such wavelength- dependent phenomena would affect the relationship between pulsational and radial velocities and the derived surface brightness (Baade-Wesselink) distances for Cepheids. In a further investigation of this problem, radial velocity curves and line profile asymmetries have been obtained from 100 absorption lines in the near-IR (8000 A deg) for the bright Cepheids δCep (5 day period), ηAql (7 day), and X Cyg (16 day). A fiducial wavelength scale has been provided by the embedded telluric absorption lines. The relative radial velocity errors of individual stellar absorption lines have been reduced to a few hundred meters per second.