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 new V-R color indices for 17 of these. Improved albedos, derived from the new absolute magnitudes, have been obtained for 10 Hilda asteroids. The V-R color 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.