A Study of Hilda Asteroids: V. Lightcurves of 47 Hilda Asteroids

Abstract

The results of a photometric survey of Hilda asteroids are presented. We have obtained 224 lightcurves of 47 Hilda asteroids. A wide span of rotation periods have been found, ranging from 2.851 to 31 h. However, indications of rotation periods longer than 100 h were found for two objects. The largest lightcurve amplitude found is 1.38 mag, and 13 additional objects have observed amplitudes ≥0.30 mag. Improved absolute magnitudes have been obtained for 20 objects as well as newV–Rcolor indices for 17 of these. Improved albedos, derived from the new absolute magnitudes, have been obtained for 10 Hilda asteroids. TheV–Rcolor indices range between 0.38 and 0.49 mag, indicating that only P- and D-type asteroids are present among these asteroids. A probable taxonomy was assigned to four Hilda asteroids (one P-type and three D-types) which previously were unclassified. The Hilda Asteroid 3694 Sharon was observed at low solar phase angles, and the obtained lightcurves indicate a reduced to nonexisting opposition effect for this asteroid. One Hilda asteroid, 2067 Aksnes, may be in a state of precession as no satisfactory two-maxima and two-minima lightcurve could be fitted to the data. However, the short damping time scale makes this very unlikely. This favours a four-maxima and four-minima lightcurve of 2067 Aksnes, which is a better fit to the data than a two-maxima and two-minima lightcurve. The Hilda Asteroid 3415 Danby has a very short rotation period (P= 2.851 ± 0.003 h), making Danby the fastest spinning asteroid known within its size range (D∼ 50 km). Due to its fast spin some constraints can be set on 3415 Danby's internal structure and mean density. The assumption that 3415 Danby is a rubble-pile, with its shape governed by hydrostatic equilibrium, leads to an unrealistically high mean density. On the other hand, assuming that 3415 Danby has internal strength results in a mean density larger than 1.4 g cm−3.