2003 UB_313

J.-M. Petit, Observatoire de Besancon; M. Holman, Harvard- Smithsonian Center for Astrophysics; and B. Gladman, University of British Columbia, report photometric observations of 2003 UB_313 (cf. IAUC 8577). Holman obtained 120-240-s exposures during July 30.285-30.437 and 31.322-31.420 UT with the 6.5-m Baade telescope (+ Inamori Magellan Areal f/4.3 Camera and Spectrograph + Bessell R filter) at Las Campanas. Gladman obtained 30-120-s exposures during Aug. 2.278-2.435 and 3.330-3.382 with the 8.2-m UT-1 Very Large Telescope (+ FORS2 camera + specialized Bessell R filter) at Cerro Paranal. Aperture photometry performed by Petit shows evidence of variability at the 0.015-mag level within two individual nights of observation. The night-to-night variations from July 30 to 31 and from Aug. 2 to 3 are of the same order. Data do not cover an arc long enough to determine a period, but if the variations are due to rotation, then the period exceeds 8 hr. However, the observed variation might be due to other effects, such as unknown color terms.