The IMACS Occultation Survey: I. Pilot Study

We report the results of a pilot study, searching for occultations of background stars by small (sub-km) Kuiper belt objects (KBOs). Our study is ground-based, using the Inamori Magellan Areal Camera and Spectrograph (IMACS) instrument on the 6.5m Magellan Baade telescope, at Las Campanas Observatory in Chile. We implemented a novel shutterless continuous readout mode on the IMACS instrument, with custom-made aperture masks, permitting simultaneous high-speed (36 Hz) photometry for numerous stars, while minimizing the effects of stellar crowding and sky background. Observing in the southern hemisphereallows us to target the intersection of the ecliptic and galactic planes, where hundreds of stars can be monitored with a single field of view. We observed for a total of ~28 hours spread over eight nights, obtaining ~11,000 star-hours of light curves with per-point SNR > 10. This represents an order of magnitude increase in star-hours compared to the previous best ground-based survey by Bianco et al. (2009). Our results allow us to place strong constraints on the surface density of sub-km objects in the Kuiper-Belt, as well as to complement the HST FGS results of Schlichting et al. (2009, 2012).