Photometry of the Kuiper-Belt object 1999 TD10 at different phase angles

We present photometric observations of the Kuiper-Belt object 1999 TD 10 at different phase angles and for three different broad band filters (B, V and R). This object was observed with the Danish 1.54-m telescope of ESO in Chile during six different observing nights corresponding to a phase angle of 0.30, 0.37, 0.92, 3.43, 3.48 and 3.66°. Extra observations were obtained in September 2002 with the VLT UT1/FORS1 combination to confirm that 1999 TD10 does not exhibit any cometary activity, and in October 2001 with the Sierra Nevada Observatory 1.50-m telescope in order to add relative magnitudes to improve the determination of the rotation period. The observations are compatible with a single-peaked rotational lightcurve with a 7h41.5min ± 0.1 min period or a double-peaked lightcurve with a 15h22.9min ± 0.1 min period. If a single-peaked rotational lightcurve is assumed the amplitude is 0.51 ± 0.03, 0.49 ± 0.05 and 0.60 ± 0.09 mag for the R, V and B bands, respectively. We present the phase curve obtained when assuming that the lightcurve is single-peaked. This phase curve reveals clearly an increase of about 0.3 mag and of similar importance for the three bands when phase angle decreases from 3.7° to 0.3°. The phase curve reveals a linear increase of the brightness with the decreasing phase angle and, consequently, does not permit a modeling of the opposition surge. Neverthless the poor repartition of the observational data does not permit a firm conclusion concerning the presence or absence of an opposition surge on the phase angle range covered by our data. Complementary observations are needed.