A Photometric Survey of Centaur and Trans-Neptunian Objects

S.C. Tegler (Northern Arizona Univ), W. Romanishin (Univ Oklahoma), D.A. Weintraub (Vanderbilt Univ), U. Fink, R. Fevig (Univ Arizona)

We present a progress report on our program at the Steward Observatory 1.5-m and 2.3-m telescopes, the NASA Infrared Telescope Facility, and the Kitt Peak National Observatory 4.0-m telescope to carry out a B, V, R, J, H, and K band photometric survey of Centaur and Trans-Neptunian Objects (TNOs). The goals of our program are to: (1) constrain the sizes and shapes and spin axis orientations of these objects, and (2) determine whether these objects exhibit a diversity of colors and therefore a diversity of surface compositions.

We have constrained the sizes and shapes and spin axis orientations of the TNOs 1993 SC and 1994 TB and the Centaur 1995 GO. If we assume the axes of rotation are ortogonal to our line of sight, then 1993 SC is spherical (semi-major to semi-minor axis ratio, a/b tex2html_wrap_inline11 1.12) and 1994 TB and 1995 GO are elongated (a/b tex2html_wrap_inline13 1.4). We find that the TNOs 1993 SC and 1994 TB and Centaurs 1993 HA2 and 5145 Pholus have extraordinarily red B-V and V-R colors, among the reddest in the Solar System. Extraordinarily red colors are consistent with surfaces rich in complex carbon-bearing molecules. The B-V, V-R, V-J, and J-K colors of 1995 GO are much less red (similar to redder Trojan asteroids).

In the future, once we have a statistically significant number of observations, we will look for a Centuar and TNO color trend with perihelion distance. In addition, we will examine individual Centaurs and TNOs for a color trend with longitude. From such an analysis we will constrain the importance of cosmic ray bombardment, collisions, and coma formation on the surface evolution of Centaurs and TNOs.

This research is supported by the NASA Origins of Solar Systems Program.