Infrared high angular resolution measurements of stellar sources ^*

VI. Accurate angular diameters of X Cnc, U Ori and Eta Gem

¹ European Southern Observatory, Karl-Schwarzschildstr. 2, 85748 Garching bei München, Germany
² Osservatorio Astrofisico di Arcetri, L.go Enrico Fermi 5, 50125 Firenze, Italy

Corresponding author: A. Richichi, arichich@eso.org

Received: 25 October 2002
Accepted: 27 November 2002

Abstract

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 η Gem (M3III). Their 2.2 μm angular diameters, derived under the assumption of a uniform circular disk, are , and 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 η Gem, significant differences exist among the available angular diameter determinations.