Spectral classification at ultra-low dispersion

Abstract

The accuracy of the ultralow-dispersion slitless-spectroscopy technique of Bappu and Parthasarathy (1977) in classifying early-type stars at great distances from the sun is investigated experimentally using a 5-min exposure of NGC 2362 obtained at dispersion 1 micron/mm on a IV-E emulsion (limiting magnitude 13.5 mag in V and 13.0 mag in B). Data on 37 stars are presented in tables and graphs and compared with published observations. The method is found to give fairly accurate classifications when there is minimal interstellar extinction and to be well suited to the identification of regions with early-type stars, the determination of cluster membership, and the detection of distant clusters in windows of low extinction in the Galaxy.