VARIABLE PHASE-FACTORS AND COLOR INDEXES DURING THE ROTATION OF 51-NEMAUSA AND A COMPARISON OF 6 APPARITIONS

The phase factor varied between 0.032 and 0.045 mag/deg on the differe nt sides shown during the rotation of the asteroids 51 Nemausa in the 1990 opposition. Color index variations with amplitudes 0.015 mag in u -b and 0.004 mag in v-y confirm the variations found in 1989. The effe cts are single periodic with one extremum and are caused by difference s in composition and texture over the surface. Differences between the opposite pairs 1983-1989, 1985-1990 and 1986-1991 show identical devi ations from the theoretical sine curve.