2003A&A...399..275R

We present the results of near-IR lunar occultation measurements of three well-known, large angular diameter, cool giant stars, namely X Cnc (CII), U Ori (M8III) and eta Gem (M3III). Their 2.2µm angular diameters, derived under the assumption of a uniform circular disk, are 8.26±0.04, 15.14±0.05 and 12.57±0.04 milliarcsec, respectively. In the case of U Ori, we find a significant deviation of the brightness profile from circular symmetry, as well as a faint signature of extended emission. The asymmetry of the brightness profile cannot be explained by scintillation effects in the lunar occultation lightcurve, and could have contributed to the important differences in previous determinations of the angular diameter of U Ori in the near-IR. Also in the case of eta Gem, significant differences exist among the available angular diameter determinations.