Pencil-Beam Surveys for Faint Trans-Neptunian Objects

Abstract

Motivated by a desire to understand the size distribution of objects in the Edgeworth-Kuiper belt, an observing program has been conducted at the Palomar 5 m and Canada-France-Hawaii 3.6 m telescopes. We have conducted pencil-beam searches for outer solar system objects to a limiting magnitude of R ~ 26. The fields were searched using software recombinations of many short exposures shifted at different angular rates in order to detect objects at differing heliocentric distances. Five new trans-Neptunian objects were detected in these searches. Our combined data set provides an estimate of ~90 trans-Neptunian objects deg^-2 brighter than 25.9. This estimate is a factor of 3 above the expected number of objects based on an extrapolation of previous surveys with brighter limits and appears consistent with the hypothesis of a single power-law luminosity function for the entire trans-Neptunian region. Maximum-likelihood fits to all self-consistent published surveys with published efficiency functions predicts a cumulative sky density Σ(<R) obeying log Σ = 0.76(R - 23.4) objects deg^-2 brighter than a given magnitude R.