Abstract

A system of photoelectric photometry is outlined which utilines the revised zero point of the visual magnitude scale of the North Polar Sequence and which returus to the original definition for the zero point of color indices in terms of main-sequence stars of class A0; the interval A0-gK0 is 1 mag. The revised Yerkes Atlas system (MK) of spectral classification is taken as standard. The latter is described briefly, and a list of standard stars is included. Magnitudes and color indices from measures in three wave4ength bands are given for stars selected by spectral type and luminosity class to be representative of the principal regions of the H-R diagram. A few white dwarfs are also included. A standard main sequence is defined for the new color-absolute magnitude diagram by the use of stars of large parallax, together with the galactic clusters NGC 2362, the Pleiades, the Ursa Major nucleus, and Praesepe. A standard mnin sequence is also defined for the relationship between the two systems of color index. A purely photometric method for determining spectral types and space reddening for B stars in galactic clusters is described.