Angular diameters of dzeta Aurigae-type supergiants by by Michelson interferometry.

Interferometric observations are reported for the cool supergiants Zeta Aur, 31 Cyg, and 32 Cyg, first resolved by the 12T interferometer (CERGA) operating at NIR wavelengths. Limb-darkened angular diameters of 5.5 + or - 0.3, 5.7 + or - 0.6 and 5.5 + or - 0.5 marcsec, respectively, are derived for the three stars. Since those supergiants are members of well-known eclipsing binaries, their linear sizes may be obtained, by combining interferometric results with occultation data from eclipse timing and orbital velocity. The resulting stellar radii are: 154 + or - 13, 169 + or - 20 and 215 + or - 33 solar radii, respectively.