NASA Astrobiology Institute (NAI)

We are stacking ultra-deep images obtained using the wide-field Suprime-Cam imager on the Subaru telescope to measure the size distribution of small (~10 km) Kuiper Belt objects. Previous measurements of the size distribution have been limited to brighter magnitudes, but this survey exploits the sensitivity and wide field coverage of Suprime-Cam to reach a limiting magnitude >25 over a square degree, allowing us to study the distribution of very small objects.

We are using the stacking techniques that we developed in our recovery attempt of 85P/Boethin for the EPOXI mission to stack four fields of Subaru Suprime-Cam data, taken over two nights. By stacking on a fine grid of rates, we will be able to detect KBOs moving at a range of orbital speeds. Our noise-suppression techniques of static sky subtraction and star-masking developed for 85/P are being used to minimize false noise detections, and cross-matching of detections between the two nights further suppresses false positives.

We then compute the true (excess over noise) detection rate using the twin null-tests of considering retrograde motion, and of perturbing night 1 in relation to night 2 to break their correspondence and leave only random matches.

Figure 1 shows preliminary recoveries of simulated data inserted into our Suprime-Cam fields. We are able 1) to recover objects to a VR magnitude of 28 with 40% completeness; 2) to estimate the distances of the recovered objects to an accuracy of about 1 AU; 3) to achieve a small scatter in magnitude, after accounting for a systematic light loss; 4) to recover the inclination of the orbit on a coarse 5 degree grid. We are still tuning the application of the technique to the actual data, and are working to remove remaining systematic biases.