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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[12.03] Procyon: Constraining Its Temperature Structure with High-Precision Interferometry and 3-D Model Atmospheres

J. P. Aufdenberg (NOAO), H.-G. Ludwig (Lund University), P. Kervella (Observatorie de Paris-Meudon)

We have fit synthetic visibilities from 3-D (CO5BOLD + PHOENIX) and 1-D (PHOENIX, ATLAS12) model stellar atmospheres for Procyon (F5 IV) to high-precision interferometric data from the VINCI instrument at the VLT Interferometer (K-band) and from the Mark III interferometer (500 nm, 800 nm). These data provide a test of theoretical wavelength-dependent limb-darkening predictions, and therefore Procyon's atmospheric temperature structure. Earlier work (Allende Prieto et al. 2002 ApJ 567, 544) has shown that the temperature structure from a spatially and temporally averaged 3-D hydrodynamical model produces significantly less limb darkening at 500 nm relative to the temperature structure from a 1-D MARCS model atmosphere which uses a mixing-length approximation for convective flux transport. Our direct fits to the interferometric data confirm this prediction, however we find that not all 1-D models fail to reproduce the observations. The key to matching the interferometric data is a shallower temperature gradient than provided by the standard 1-D mixing-length approximation. We find that in addition to our best fitting 3-D hydrodynamical model, a 1-D ATLAS12 model, with an additional free parameter for ``approximate overshooting'', provides the required temperature gradient. We estimate that an interferometric precision better than 0.1% will be required to distinguish between the 3-D model and the ATLAS12 model. This overshooting approximation has been shown to match Solar limb-darkening observations reasonably well (Castelli et al 1997 A&A 324, 432), however published work since using Strömgren photometry of solar-type stars has cast doubt on the importance of overshooting. We have also compared synthetic spectral energy distributions for Procyon to ultraviolet, optical and near-infrared spectrophotometry and find differences from comparisons to Strömgren photometry alone.

This work was performed in part contract with the Jet Propulsion Laboratory (JPL) funded by NASA through the Michelson Fellowship Program. JPL is managed for NASA by the California Institute of Technology.

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

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