## 1. IntroductionThe asteroid 51 Nemausa attained the small phase angle 0 64 on 1994 September 24.90 and was observed at La Silla on September 25, 26 and 27 in the phase angle interval 0 64 to 1 37. In this small interval magnitudes are linear functions of the solar phase angle . The phase factors are the coefficients on and are denoted c with an index u, v, b or y for color. Phase factors are in general considered functions of but not of the rotational phase P. Our aim here is to prove that phase factors depend on the rotational phase. This confirms the phase factor variation observed in 1990 and 1991 (Kristensen & Gammelgaard (1993)). Due to the opposition effect large values were obtained for the phase factors in 1994, for instance mag/deg at rotational phase P = 0.87 rev. The first observed opposition of this object was in 1858 and the 1994 opposition is numbered 100. It is, however, the very first opposition where an ephemeris for physical observations is available. This is a very great advantage for the reduction and interpretation of photometric observations. © European Southern Observatory (ESO) 1997 Online publication: June 5, 1998 |