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R.R. Thompson (Jet Propulsion Laboratory / U. Wyoming), M.J. Creech-Eakman (Caltech / Jet Propulsion Laboratory), PTI Collaboration
We report evidence of departures from spherical symmetry in a sub-sample of the mira dataset taken with the Palomar Testbed Interferometer (PTI). The criteria for testing such departures is two-fold: first, that the visibility data using the N-S and N-W baselines be taken within 0.1 of a mira's pulsation phase (to rule out dramatic size changes); and second, that extensive hour coverage be taken on a single baseline.
Of the 10 stars which meet this criteria, 8 show evidence of a departure from spherical symmetry when fit using a uniform elliptical disk model. It must be stressed that this "ellipticity" may only be apparent in nature, as atmospheric structures such as starspots, limb-darkening, binarity and non-radial pulsation induced outflows can influence apparent geometries of these stars. Axial ratios (2b/2a) for the model ellipses range between 0.60 and 0.90 for the eight stars.
We also report wideband (2.2 um) models of R Tri. These models - which rely upon Fast Fourier Transforms and Monte Carlo techniques - support a geometry of a slightly elliptical star with a circumstellar region of gas/dust in emission.
The work performed here was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
The author(s) of this abstract have provided an email address for comments about the abstract: thompson@huey.jpl.nasa.gov