Faint moving object detection, and the Low Signal-to-Noise recovery of Main Belt comet P/2008 R1 Garradd

Abstract

We describe the recovery of faint main belt comet P/2008 R1 Garradd using several telescopes, culminating in a successful low signal-to-noise ratio (S/N) recovery with the Gemini North telescope with GMOS. This recovery was a time-critical effort for a mission proposal, and had to be performed in a crowded field. We describe techniques and software tools for eliminating systematic noise artifacts and stellar residuals, bringing the final detection image statistics close to the Gaussian ideal for a median image stack, and achieving a detection sensitivity close to this theoretical optimum. The magnitude of Rc = 26.1 ± 0.2 with an assumed geometric albedo of 0.05 corresponds to a radius of 0.3 km. For ice to have survived in this object over the age of the solar system implies that the object is a more recent collisional fragment. We discuss the implications of the unexpectedly faint magnitude and nuclear size of P/2008 R1 on the survival of ice inside very small bodies.