Synthetic Lightcurve Signatures of Unresolved Objects: A Comparison with Observations E. V. Ryan, W.H. Ryan, C.T. Martinez, and L. Blackwell The temporal brightness variation (i.e., “lightcurve”) of unresolved targets such as asteroids and artificial satellites can be used to develop a powerful tool for general characterization studies. This information is obtainable with modest instrumentation, including off-the-shelf commercial telescopes. Analysis of these temporal signatures permits the extraction of shape, rotation period, and pole orientation for asteroids, and shape, general health status, and attitude configuration for artificial objects. In particular, a tri-axial ellipsoid model has proven to be very reliable in determining the relative dimensions of large asteroids from the inversion of lightcurve signatures (Drummond et al. 1991; Kaasalainen et al. 2001). Although the extension of this inversion process to the more complex shapes of smaller asteroids and artificial satellites provides additional challenges, especially when the target’s shape has convex features, techniques are being developed to address this as well (Ostro et al. 1988; Kaasalainen et al. 2004?; Lambert et al. 2004). However, in general, the problem of inverting lightcurve data to determine a unique shape remains a challenging task for irregularly shaped objects. In this analysis, we build on the large body of work done in the context of asteroid studies, and investigate an iterative approach to the identification and characterization of unresolved targets. We have developed a synthetic lightcurve direct model that, theoretically (assuming that the correct scattering properties and physical attributes are included) results in a unique lightcurve signature even for the most complex objects. This model can be used to construct a library of lightcurve signatures for a variety of sample objects which in turn can be used to provide initial guesses for the input parameters to an inverse model. The resulting inverse-predicted shape is then put back into the direct model, compared with observations, and refined as needed. We present the results of applying this technique to both asteroid and artificial satellite targets. In particular, we demonstrate how this has allowed us to identify the existence of a binary companion to the main belt asteroid 3782 Celle (Ryan et al. 2004). We then compare the accuracy of model predictions from data obtained with meter-class telescopes and a portable, 0.35-meter commercially available instrument. As part of this research, we plan to build upon the single-site lightcurve inversion work done by Lambert et al. (2004) by acquiring simultaneous lightcurve observations of selected targets at multiple sites having differing viewing geometries. References Drummond, J. D., S. J. Weidenschilling, C. R. Chapman and D. R. Davis, 1991, Photometric geodesy of main-belt asteroids. IV - An updated analysis of lightcurves for poles, periods, and shapes, Icarus 89, 44-64. Kaasalainen, M., J. Torppa, and K. Muinonen, 2001, Optimization methods for asteroid lightcurve inversion. II. The complete inverse problem, Icarus 153, 37-51. Kaasalainen, M., P.Pravec, Y.N. Krugly, L. Šarounová, J. Torppa, J. Virtanen, S. Kaasalainen, A. Erikson, A. Nathues, J. Durech, M. Wolf, J.S.V. Lagerros, M. Lindgren, C. Lagerkvist, R. Koff, J. Davies, R. Mann, P. Kušnirák, N.M. Gaftonyuk, V.G. Shevchenko, V.G. Chiorny, and I.N. Belskaya, 2004, Photometry and models of eight near-Earth asteroids, Icarus 167, 178-196. Lambert, J., K. Luu, and E. Brevdo, 2004, Direct inversion of visible and infrared signatures, Proceedings of the 2004 AMOS Technical Conference, Hawaii. Ostro, S.J., R.Connelly, and M. Dorogi, 1988, Convex-Profile Inversion of Asteroid Lightcurves, Icarus 75, 30-63. Ryan,W.H., E. Ryan, and C. Martinez (2004). 3782 Celle: Discovery of a Binary System within the Vesta Family of Asteroids. Planetary and Space Science, 52, 1093 -1101.