Spectral and Luminosity Classifications and Measurements of the Strength of Cyanogen Absorption for Late-Type Stars from Objective-Prism Spectra.

Abstract

Objective-prism spectra of 684 stars of spectral type G8-K2 have been classified for luminosity and cyanogen absorption. The spectra have been obtained with the Curtis Schmidt telescope of the University of Michigan, using the combined 40 and 60 prisms. The luminosity estimate is based on the strength of the X 4077 line of ionized strontium, while the cyanogen absorption is measured by the break in density at the cyanogen band head at X 4216. Ten per cent of the giants are classified as "weak CN" stars Slit spectrograms have been obtained for 37 program stars (including 29 weak and slightly weak CN giants) with the 60-inch reflector of Mount Wilson Observatory. Absolute magnitudes were obtained from direct-intensity microphotometer tracings. Space velocities have been determined for over 200 stars, for which radial velocities are available. The frequency distribution of space velocities for the weak CN giants has a higher dispersion than the frequency distribution for giants with normal cyanogen absorption. The weak CN giants are also less concentrated toward the galactic plane than the giants with normal cyanogen absorption.