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E. S. Barker, J. G Ries (U. Texas at Austin, McDonald Observatory), P. J. Shelus (U. Texas at Austin, Center for Space Research), F. Varadi (U. California at Los Angeles, Inst. for Geophysics and Planetary Physics)
The NASA Near Earth Object (NEO) search efforts have now discovered more than 2300 objects, ~500 of which are classified as Potentially Hazardous Asteroids (PHAs). Physical characteristics such as mass, rotation rate and surface properties are important factors in understanding the full dynamical evolution of NEOs. At the present we lack sufficient information on the physical characteristics of most NEOs.
As a first step, we are attempting to obtain refined absolute magnitudes, rotational periods, and, whenever possible, axis ratios and three-color information for PHAs. We have observed PHA 2002 EZ11 for about six hours on February 17, 2003. Carrying out relative photometry on the 94 images, we detected a total peak to valley brightness variation of 0.15 magnitude in the Johnson R filter with an internal precision of ±0.02 mag. A rotational period of 1.15 hours was determined by a simple least square fit. A similar rotation period of 1.16 hours was fitted using Singular Spectrum Analysis (SSA; Ghil et al., 2002, “Advanced spectral methods for climatic time series”, Reviews of Geophysics, 40, 1-41), which has proven to perform quite well on short and noisy time series. Instead of fixed sinusoids, SSA uses data-adaptive basis functions to decompose the time series. The original data can be rather noisy but the analysis detects any oscillatory pattern with varying amplitude.
We have collected similar datasets for 2002 AM31, 2002 CE, 2003 CJ11, 2003 CY18, 2003 KO2, and (7335) 1989 JA. Analyses to determine the limits of the variability, and if possible, constructing lightcurves are in progress. Over the last year we have also collected B, V and R color information for 15 asteroids. Color indices as well as initial fitting of brightness variations will be presented at the meeting.
This research is funded by NASA's NEO Observation Program grants NAG5-10183 and NAG5-13302.
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Bulletin of the American Astronomical Society, 35 #4
© 2003. The American Astronomical Soceity.