Photometric Studies of Asteroids.VI. Photographic Magnitudes.

A general survey of asteroid magnitudes is made. Systematic differences between results published by different observatories may attain 3 mag. The magnitudes in the are systematically from 1 to 2 mag. brighter than those on the International photographic system and have a probable error of 10.3 mag.; the detailed relation is shown in Figure 9. The importance of the use of photoelectric standards is stressed. Some procedures are suggested, and corrections for field effects and for image trailing are examined. A simple method of reduction to absolute magnitude, useful also in photoelectric work, is described. Observations were made with the 24-inch reflector for magnitudes of Trojans and phase effects of asteroids. From 22 asteroids all average phase factor was determined of 0.023 mag/deg between 10 and 20 phase angle. It was found that the factor is much larger at phase angles smaller than 5 . Mean magnitudes of the Trojans were derived by a combination of several observed values; in this manner a probable error of about 10.08 mag. was reached.