Polarimetry of asteroid 2100 Ra-Shalom at large phase angle

Two-color polarimetric observations of C-type asteroid 2100 Ra-Shalom were conducted when its phase angle was 59.7 degrees. No other C-type asteroid h as so far been observed at such a large phase angle. We relate the new data point to the available data on C-type asteroids and on Phobos and Deimos a nd compare the phase curve of these objects with the phase curve of dusty c omets. The observed polarization of Ra-Shalom is slightly lower than expect ed from a common curve of the other C-type asteroids and the martian moons. We conclude that this may be caused by the immature regolith on the surfac e of this small asteroid. (C) 1999 Academic Press.