Infrared lightcurves of asteroids 532 Herculina and 45 Eugenia: Proof of the absence of significant albedo markings

Time-resolved near-infrared (J and K bands) and mid-infrared (N and Q bands) photometric measurements of asteroids 532 Herculina and 45 Eugenia show reflected and thermal lightcurves that are in phase: i.e., thermal maxima and minima occur at nearly the same time as the maxima and minima in reflected light. Model lightcurves for Herculina based on the albedo distribution of Taylor et al. (1987, Icarus 69, 354-369) are predicted to be 90° out of phase. A comparison of the model and observed lightcurves leads us to conclude that the light variations of Herculina and Eugenia are due primarily to shape rather than to surface albedo variations.