AAS 205th Meeting, 9-13 January 2005
Session 12 Stellar Atmospheres
Poster, Monday, January 10, 2005, 9:20am-6:30pm, Exhibit Hall

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[12.05] "Diameters of Mira Variables at PTI (1999-2004) - Evidence for asymmetries in both geometric and temporal pulsation"

R.R. Thompson (Michelson Science Center-Caltech), M.J. Creech-Eakman (New Mexico Tech, Dept. of Physics)

Since 1999, the Mira variable program at the Palomar Testbed Interferometer has been obtaining visibility data on over 100 Miras, resulting in over 26,000 wideband diameter measurements in the K-band alone. (The narrowband companion dataset, in 5 channels across the K-band, has over 130,000 diameter measurements.) Roughly 25% of the stars have been tracked through multiple periods; as such, regularities in pulsation are detected in the dataset. One such regular Mira is R Boo (M4e), with diameter changes showing geometric and temporal regularity over 7 cycles, regardless of baseline orientation (Thompson et al, 2004).

In contrast, many of the multi-epoch datasets show evidence of departures in regularity, either geometrically or temporally, or both. The geometry of Y Del (M8e) has axisymmetry, and shows clear evidence of amplitude size changes (Creech-Eakman & Thompson, 2004). R Del (M5e) shows temporal asymmetries, with a slow angular expansion followed by a shallow contraction. Still others, like T And (M3e), show seemingly stochastic angular size changes which can't be modeled in any simple way. The stellar photospheric properties of these stars and others will be discussed, as well as the chemistry of the extended molecular atmospheres which surround these enigmatic stars.

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© 2004. The American Astronomical Society.