AAS 202nd Meeting, May 2003
Session 32 Stellar Atmospheres and Circumstellar Material
Poster, Tuesday, May 27, 2003, 10:00am-6:30pm, West Exhbit Hall

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[32.06] Angular Sizes for G7-M6 Giants in the Near-Infrared: Observations Compared to Model Atmospheres

G.T. van Belle, D.R. Ciardi (Michelson Science Center - Caltech), M.J. Creech-Eakman, R.R. Thompson (Jet Propulsion Laboratory), PTI Collaboration

We present angular size measurements obtained with the Palomar Testbed Interferometer (PTI). Our sample includes 103 giant stars, with spectral types between G7 and M6. These objects represent the `well studied' subset of giant stars observed at PTI (> 4 samples per star, with an average of 17 samples per star). These objects have been rigorously vetted for binarity against the Hipparcos and FK6 catalogs. The PTI observations present `narrowband' angular sizes in 0.1 \mum increments across the K band, from 1.95 to 2.45 \mum, with narrowband channel centers located at 2.0, 2.1, 2.2, 2.3, and 2.4 \mum. There is strong evidence with later spectral types for a systematic increase in their 2.4 \mum sizes relative to the 2.2 \mum near-continuum center pixel, with weaker evidence for a similar effect in the 2.3 \mum channel. There is little if any evidence for similar size differences between the 2.0 and 2.1 \mum channels, relative to the band center. By comparing this data to publicly available near-IR spectrophometric data for stars of similar spectral type, there is a clear correlation between the strength of spectral features, including the 12CO and 13CO bands that set in longwards of 2.29\mum, and the narrowband angular size differences. Giant star atmospheric models corresponding to the PTI `narrowband' visibility data were generated from the extended model photospheres found in Bessel et al. (1989, 1991). For both the models and the observations, size ratios between the outlying wavelength pixels relative to the 2.2 \mum center pixel may be generated, along with effective temperature (TEFF) estimates, and then compared. We find that for the stars with TEFF between 3000K and 4000K, the observed 2.4\mum / 2.2\mum size ratios are significantly higher than predicted by the models.

This work is funded by the NASA Origins Program through JPL and Caltech.

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The author(s) of this abstract have provided an email address for comments about the abstract: gerard@ipac.caltech.edu

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Bulletin of the American Astronomical Society, 35 #3
© 2003. The American Astronomical Soceity.