Spin vector and shape of 532 Herculina

Herculina has been observed during 7 oppositions: 1954 (Groeneveld and Kuiper), 1963 (Chang and Chang), 1978 (Harris and Young), 1982 (Drummond et al.; Weidenschilling et al.), 1984 (Taylor et al.), 1985 (Erikson et al.), and 1987 (Lebofsky et al.; Weidenschilling et al.). This asteroid has very unusual lightcurves. They exhibit two maxima and minima in 1978, 1984, and 1987, and only one maximum and minimum in 1954, 1963, and 1982 per rotation cycle of about 9.4 hours. The 1985 lightcurve, which is very close in aspect to those from 1963, shows two maxima and minima. The primary minimum is very similar to a single minimum in 1963, while the secondary one is only 0.06 mag deep. In 1963 no secondary minimum was visible.