OPTICAL-SPECTRA OF ZETA-AURIGAE BINARY-SYSTEMS .7. THE 1987 AND 1989 ECLIPSES OF HR-6902

High-dispersion, high-S/N photographic spectra of the eclipsing compos ite-spectrum binary HR 6902 have been obtained during and near two pri mary eclipses. From the spectra we isolate the phase-dependent chromos pheric absorption lines, and present a list of identifications and mea surements of 133 such features. We collate eclipse photometry from fou r different eclipses, and derive the geometry of the system by modelin g the eclipse light curves. The orbital inclination is found to be 87 degrees. From the radii and the temperatures (the latter derived from applications of model atmospheres) we calculate the absolute magnitude s of the components. A significant mismatch between the colour indices of both components and their apparent spectral types indicates that t he system is seen through about 0.(m)6 of interstellar absorption, whi ch had not been appreciated in earlier studies. Measured chromospheric radial velocities show a spread suggestive of large-scale motions wit hin the chromosphere.