A study of Trans-Neptunian object 55636 (2002 TX300)

We report on physical properties of the bright Trans-Neptunian Object 2003 TX300 based on a large set of observations taken in different wavelength ranges. Broad hand CCD observations aimed at studying the short-term rotational variability show a low amplitude periodic signal of 7.89 +/- 0.03 h. We cannot yet determine whether the lightcurve is single-peaked (i.e. the rotation period Would be 7.89 h) or double-peaked (i.e. the actual spin period would be 15.78 h). From a sinusoidal fit, the peak to peak amplitude of the brightness changes is 0.09 +/- 0.08 mag. If the brightness changes are due to irregular shape, this amplitude implies a minimum axial ratio of 1.09. BVRI photometry indicates similar colors as other large Kuiper Belt members. with B-V = 0.64 +/- 0.04, V - R = 0.40 +/- 0.07, and R - I = 0.22 +/- 0.05. Thermal observations at 250 GHz (1.2 mm) result in no confident detection of the body, with a measured flux of 0.22 +/- 0.51 mJy. Combining all the data and using the same thermophysical model as in Lellouch et al. (2002) we find (at a 3-sigma confidence level) a lower limit for the geometric albedo (p(upsilon) > 0.06) and an Upper limit for the size of this object (D < 1110 km). A more relaxed 2-&sigma; confidence level implies a diameter D < 907 km and an albedo p(upsilon) > 0.08. which is significantly higher than the typical 0.04 cometary value and also higher than that of Varuna.