Two-Dimensional Classification of the HD Stars

Abstract

The major project of assigning spectral and luminosity classes to the Henry Draper stars south of +30° is underway. The high-quality objective-prism plates have been taken with the Michigan Curtis Schmidt telescope at Cerro Tololo Inter-American Observatory. The spectra, widened to .8 mm, have a dispersion of 108 Å mm-1 at Hγ. Plates exposed for 20m and for 4m + 1m yield classifiable spectra between 4 and 10 mpg.Star identification is completely automatic, using a computer-generated plot to the Schmidt plate scale for each plate center. This plot, having the HD stars identified by number, is copied onto transparent material and placed under the Schmidt plate while the stars are visually classified.Classification is being carried out by one person (N.H.) to maintain a uniform system. MK spectral standards of similar quality and density, also taken with the Schmidt, are continually referred to. Intercomparison of the new types with existing spectral types shows no systematic differences. However, the HD types themselves are systematically earlier in the range A to F.Stars between the south celestial pole and δ = −55° are being classified first, with the first volume of results to be published late in 1973. It is expected that the catalogue of spectral types and remarks will be published in 6 volumes containing all HD stars south of +30°.This research is being supported by the National Science Foundation.