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R.R. Thompson (JPL / U. Wyoming), M.J. Creech-Eakman (Caltech / JPL), A.F. Boden (IPAC / JPL), G.T. van Belle (JPL), PTI Collaboration
As part of the long-term observational program of Mira variables at the Palomar Testbed Interferometer (PTI), we report angular size measurements (uniform disk) of 50 such stars in the near-infrared. These data represent direct measurements, both spatially-resolved (1.5-4.5 mas) and spectrally-resolved in 0.1 um bins spread over five channels in the K-band. Diameters taken in four spectral channels spread over the H-band are also presented.
Distinctions in the spectral angular diameter character with respect to visible phase are made between oxygen-rich (N=32), intermediate (N=9) and carbon-rich (N=10) classes. Utilizing the AFOEV and AASVO databases to determine the phase in visual light, periodic changes in the 2.2um diameter with respect to the band edges (2.0um and 2.4um) are seen for O-rich Miras. However, a more uniform angular size structure is seen in C-rich Miras; exceptions to this uniformity exist in the 2.4um channel. Comparisons are made to O-rich and C-rich non-Mira giants, which do not exhibit these characteristics so dramatically, or not at all. We also highlight examples of a few stars which depart from a spherical uniform disk model.
The data within represent nearly 500 individual observations over the 1999-2000 PTI observing seasons. This work is part of the Mira observational program at PTI to investigate the chemistry (C/O ratio, metal abundance), period length, and strength of the acoustic shock as evidence for the mode of pulsation.
The work performed here was conducted at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration.
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