Size estimates of some optically bright KBOs

Seven recently detected optically bright Kuiper-Belt-Objects (KBOs) were observed at 250 GHz using the Max-Planck Millimeter Bolometer (MAMBO) array at the IRAM 30 m telescope. Only the optical binary KBO (47 171) 1999 TC36 was detected, whose components differ optically by Deltam approximate to 2 mag. Assuming that the derived mean geometric albedo of p = 0.05 is identical for both, the component diameters become 566 and 225 km. For the other six objects upper limits to their sizes and lower limits for their albedos were obtained. The geometric albedo, p, for (28978) Ixion is surprisingly large, greater than or equal to0.15. For a consistent comparison all published radio photometric data of KBOs and Centaurs were analyzed again: the average geometric albedo is found to be approximate to0.08.