Photoelectric Studies. VIII. Positional Effect in Photomultipliers and Some Revised Magnitudes in the North Polar Sequence and Harvard Region C 12.

It has been found that the 1P21 photomultiplier varies in sensitivity, depending on its orientation in the earth's magnetic field. This "positional effect" has been eliminated by shielding the photomultiplier with demagnetized strap-iron. The only magnitudes in the previous seven papers of this series that are seriously affected by the positional effect are those in Paper I for the North Polar Sequence. New magnitudes for some of these polar stars have been determined (Table 2). Otherwise no change is required in all other magnitudes in Papers 1-VIl, which are uniformly on a consistent system referred to Harvard Standard Region C 12. A standard radium light-source has been used to control the observations of stars in widely different parts of the sky. Improved magnitudes and colors, Pg and Cp, for the stars in Region C 12 differ at most by 0.02 or 0.03 mag. from the values used in previous papers (Table 1). Equations (1) and (2) give the conversion of Pg and Cp to the system of Stebbins, Whitford, and Johnson, which is based on nine stars of the North Polar Sequence. The change of the zero point in this conversion would make all apparent and absolute magnitudes in Papers 1-vIl fainter by 0.14 mag.