The analysis gave over two hundred phase curves for 74 asteroids. We have studied them all graphically. In Fig. 2 (click here) we show four representative examples. The results are summarized numerically in Table 5.
A major problem with phase curve fitting is that for objects that do not follow closely the HG-law the determined H and G-value will depend on the solar phase angle range used.
Table 2: Mean slope parameters G for different taxonomic groups
ordered according to there albedo.
For each group and reference, N is the number of asteroids included,
<G> is the average G-value and ``Disp'' is the corresponding dispersion
The phase curves are quite linear in 15 cases out of 74 asteroids included in this study (see Fig. 2a for an example). For these the HG-fit is misleading and may predict non-existent physical properties. The linearity of the phase curve is most evident for (5) Astraea, (9) Metis, (12) Victoria, (27) Euterpe, (51) Nemausa, (88) Thisbe, (129) Antigone and (511) Davida. The linearity does not seem to depend much on taxonomic type.
Indications of opposition spikes, which could be caused by coherent backscatter of surface material (Muinonen 1990; Skhuratov & Muinonen 1991), is evident for (28) Bellona, (37) Fides, (44) Nysa, (77) Frigga, (97) Klotho, (196) Philomela and och (349) Dembowska (see Fig. 2b for an example).
Table 2 (click here) shows average slope parameters G for different taxonomic categories. Our data is in good agreement with previous results (Harris & Young 1988; Lagerkvist & Magnusson 1990; Lagerkvist et al. 1992). Although the dispersion of G-values for individual taxonomic types is quite big the G-values is a useful indicator of the approximate albedo.