2001A&A...380..526R

In the framework of an ongoing series of high angular resolution observations by lunar occultations in the near infrared, we present accurate angular measurements for ten late-type giant stars, seven of which were measured for the first time. The sample includes one K and seven M stars. It also includes two S stars, representing to our knowledge the first direct determination of the angular diameter for this class of stars. The measured angular diameters range from 2.50 to 4.82 milliarcsec, with an average accuracy <5%. An exception is represented by the case of a star with a faint companion, where we have been able to investigate in detail the bias on the diameter determination, and hence on the effective temperature, which would be caused if the companion had not been included in the analysis. We suggest that faint undetected companions could explain at least some of the hitherto known cases of stars with effective temperatures remarkably lower than the standard calibration. For seven of the stars in the sample, we have used our own photometry in conjunction with values from the literature, to compute the bolometric fluxes and the effective temperatures, which we discuss in the context of existing calibrations. With the achieved accuracy level in the angular diameter, such measurements are also valuable as calibrators or science verification targets for modern large ground-based interferometers.