Diameters of Mira Stars Measured Simultaneously in the J, H, and K' Near-Infrared Bands

We present the first spatially resolved observations of a sample of 23 Mira stars simultaneously measured in the near-infrared J, H, and K' bands. The technique used was optical long-baseline interferometry, and we present for each star visibility amplitude measurements as a function of wavelength. We also present characteristic sizes at each spectral band, obtained by fitting the measured visibilities to a simple uniform disk model. This approach reveals the general relation J diameter <H diameter <K' diameter.