T. H. Bressi

The Search for Distant Objects in the Solar System Using Spacewatch

We have completed a low-inclination ecliptic survey for distant and slow-moving bright objects in the outer solar system. This survey used data taken over 34 months by the University of Arizonas Spacewatch Project based at Steward Observatory, Kitt Peak. Spacewatch revisits the same sky area every three to seven nights in order to track cohorts of main-belt asteroids. This survey used a multiple-night detection scheme to extend our rate sensitivity to as low as 0.012 arcsec hr-1. When combined with our plate scale and flux sensitivity (V ≈ 21), this survey was sensitive to Mars-sized objects out to 300 AU and Jupiter-sized planets out to 1200 AU. The survey covered approximately 8000 deg2 of raw sky, mostly within 10° of the ecliptic but away from the Galactic center. An automated motion-detection program was modified for this multinight search and processed approximately 2 terabytes of imagery into motion candidates. This survey discovered 2003 MW12, currently the tenth largest classical Kuiper Belt object. In addition, several known large Kuiper Belt objects and Centaurs were detected, and the detections were used with a model of our observational biases to make population estimates as a check on our survey efficiency. We found no large objects at low inclinations despite having sufficient sensitivity in both flux and rate to see them out as far as 1200 AU. For low inclinations, we can rule out more than one to two Pluto-sized objects out to 100 AU and one to two Mars-sized objects to 200 AU.

1.8-m Spacewatch telescope motion control system

The 1.8 meter Spacewatch telescope and its building on Kitt Peak were dedicated on June 7, 1997 for the purpose of finding previously unknown asteroids and comets. Drift- scanning large areas of sky with a CCD will be done at rates up to 10 times that of the sidereal rate over angles up to 60 degrees of arc along great circles at various orientations. The primary mirror and cell around which the telescope are from the multi-mirror telescope on Mt. Hopkins in Arizona. The telescopes friction drive system allows backlash-free control of its altitude-over-azimuth mount. The mount features bearings of small radii and plenty of motor torque to compensate for wind buffeting. Both incremental and absolute encoders will be used; the absolute encoders will update the position derived from incremental encoders to compensate for the microslipping that is an unavoidable consequence of a friction drive. The control system features commercially produced servo controller cards that are programmed from a user interface program running in a PC under DOS. Realtime operation of the drive is controlled by the interface cards, leaving the PC free to run the display of the position readout and accept keyboard input for the observer without interfering with the drive. It is believed that this design offers the greatest flexibility and accuracy of our search programs.

Spacewatch Astrometry and Photometry of Near-Earth Objects

The Spacewatch Project uses four telescopes of apertures 0.9-m, 1.8-m, 2.3-m, and 4-m on Kitt Peak mountain in Arizona for followup astrometry of priority NEOs. Objects as faint as V=23 on the MPC’s NEO Confirmation Page, targets of radar, potential impactors, targets of spacecraft observations or visits, and PHAs with future close approaches to Earth receive priority for astrometry.