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J. G. Ries (UT Austin/Astronomy/McDonald Observatory), E. S. Barker (NASA/Johnson Space Center), F. Varadi (UCLA/Inst. of Geophys.and Planetary Physics), P. J. Shelus (UT Austin/Center for Space Research)
The McDonald Observatory Near Earth Object (NEO) group has been involved in confirmation and follow-up efforts since 1995. Expanding this program from astrometry to astrophysics, we are attempting to derive refined absolute magnitudes, rotational periods, and, whenever possible, axis ratios for Potentially Hazardous Asteroids (PHAs). Our test case, 2002 EZ11 was observed on 2003 February 17, during full Moon (Ries et al., 2003). Using the relative photometry we analysed 76 images, and 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. The rotational period of 1.16 hours was found using Singular Spectrum Analysis (Ghil et al., 2002), which has proven to perform quite well on short, noisy time series. Some of the several other targets that we have observed are 2003 SS84 and 65803 (1996 GT). These PHAs were also observed at Arecibo and Goldstone. Our preliminary analysis of 8 hours worth of data for 65803 shows a peak-to-valley change of 0.24 magnitude, with irregular, smaller (i.e., 0.05-0.07 mag) variations superimposed. In the case of 2003 SS84 we detected a variation of 0.3 magnitude or greater in a seven hour span. The final results will be presented at this meeting.
This research is funded by NASA's NEO Observation Program Grants NAG5-10183 and NAG5-13302.
References
Ghil, M., et al. (2002), ``Advanced spectral methods for climatic time series", Reviews of Geophysics, 40, 1-41.
Ries, J.G., et al., ``Getting Physical: Rotation Rate Determination for PHAs", B.A.A.S., 1039. AAS/DDA, Ithaca, NY, May 2003.
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Bulletin of the American Astronomical Society, 36 #2
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