PENCIL-BEAM SURVEYS FOR FAINT TRANS-NEPTUNIAN OBJECTS

Motivated by a desire to understand the size distribution of objects i n the Edgeworth-Kuiper belt, an observing program has been conducted a t the Palomar 5 m and Canada-France-Hawaii 3.6 m telescopes. We have c onducted pencil-beam searches for outer solar system objects to a limi ting magnitude of R similar to 26. The fields were searched using soft ware recombinations of many short exposures shifted at different angul ar rates in order to detect objects at differing heliocentric distance s. Five new trans-Neptunian objects were detected in these searches. O ur combined data set provides an estimate of similar to 90 trans-Neptu nian objects deg(-2) brighter than similar or equal to 25.9. This esti mate is a factor of 3 above the expected number of objects based on an extrapolation of previous surveys with brighter limits and appears co nsistent 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 Sigma(<R) obeying log Sigma = 0.76( R - 23.4) objects deg(-2) brighter than a given magnitude R.