NEW DIAMETER MEASUREMENTS FOR 10 MIRA VARIABLES - IMPLICATIONS FOR EFFECTIVE TEMPERATURES, ATMOSPHERIC STRUCTURE AND PULSATION MODES

We present new and precise multi-wavelength angular diameter measurements for 10 long-period variables. After correction for limb-darkening and photospheric extension, we use these to investigate the effective temperatures, physical diameters and pulsation modes of the stars. For all 10 stars in the sample, our measurements imply photospheric radii in excess of 350 R., thereby supporting the recent result of Tuthill et al. Unless the favoured mass scale for Miras is increased by at least a factor of two, or our current understanding of their period-luminosity relation is incorrect, our data provide strong evidence against fundamental-mode pulsation in Mira variables with periods in the range 280-430 d.