Photometry of the M-type asteroid 21 Lutetia

Light curves, phase variations of magnitude and color and an improved rotation period for the M-type asteroid 21 Lutetia are presented. Two observing periods were performed, in 1981 and 1983, using 70 cm telescopes equipped with photometers. The rotation period was about 8 hr 10 m. Two sides of the asteroid differed in surface brightness by 0.07 mag due to surface albedo. The magnetic phase coefficient was within 0.001 of 0.036 mag/deg, typical for metallic surface asteroids. The visual magnitude averaged from 8.05-8.48.