Optical aperture synthetic images of the photosphere and molecular atmosphere of Mira

Abstract

We have used aperture synthetic imaging methods to obtain diffraction-limited images of the photosphere and molecular atmosphere of the long period variable star Mira (o Ceti). These maps, obtained close to the peak of Mira's variability cycle, clearly indicate substantial distortions from circular symmetry. Our image of the emission due to resonant scattering of TiO shows a significant contribution due to a cool atmosphere with a radius one and a half times as great as that of the photosphere. We suggest that the photospheric asymmetry is most likely associated with the intrinsic pulsation mode of the star and that stable nonradial pulsation modes can coexist with the radial modes that are responsible for the photometric variability. Further aperture synthetic mapping, which should be possible for a major fraction of the photometric cycle, is capable of verifying this hypothesis.