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E. S. Barker, J. Györgyey Ries, P. J. Shelus, R. L. Ricklefs (University of Texas at Austin, McDonald Observatory)
The McDonald Observatory astrometry group has been involved in Solar System positional observations since the early 1970's. Since 1995, it has evolved to a CCD-based, almost totally automated, astrometry package. We are focusing our observational program on Near Earth Objects (NEOs) as part of NASA's mission to discover and catalogue 90 percent of NEOs with diameters larger than 1 km by 2008. We carry out confirmation observations of newly discovered objects and contribute to orbit improvements of under-observed objects. Understanding the overall hazard that these objects pose to Earth requires their dynamical and physical characterization.
We recently adopted the USNO-A2.0 catalogue to improve our astrometric results. The catalog, however, also provides stellar magnitudes in the standard Johnson R and B photometric bands. After completing the night’s observing program, we now regularly provide the IAU with R magnitudes in addition to astrometric positions. Our limiting magnitude in R is near 22 in a 15 minute exposure over a 46 arcmin field on the 0.8m prime focus camera. Typically, we are scheduled for 4 nights each lunation, but our semi-automated, IRAF/ICE based program can be used by other 0.8m users.
We are testing procedures that will include B and V exposures as part of our standard confirmation triplet. We have confirmed that switching filters between exposures on standard fields does not compromise the astrometric accurary. Thus, we should be able to provide two color, sequential, relative photometry of any newly discovered asteroid, as part of the confirmation process. The time interval between exposures is less than 20 minutes, short compared to most asteroid rotation times. Consequently, a meaningful color index can be obtained in parallel with the astrometric positions. Although B-R is not the usual color index used in asteroid classification studies, we are testing whether we can use it as a quick diagnostic tool to roughly classify newly discovered NEOs as by product of our astrometric observing sequence. Preliminary results will be presented at the meeting.
This research is funded by NASA’s NEO Observation Program grants NAG5-6863 and NAG5-10183.