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

• We have fit synthetic visibilities from 3-D (CO5BOLD +PHOENIX) and 1-D (PHOENIX, ATLAS12) model stellar atmospheres forProcyon (F5 IV) to high-precision interferometric data from the VINCIinstrument at the VLT Interferometer (K-band) and from the Mark IIIinterferometer (500 nm, 800 nm). These data provide a test oftheoretical wavelength-dependent limb-darkening predictions, andtherefore Procyon's atmospheric temperature structure. Earlier work(Allende Prieto et al. 2002 ApJ 567, 544) has shown that the temperaturestructure from a spatially and temporally averaged 3-D hydrodynamicalmodel produces significantly less limb darkening at 500 nm relative tothe temperature structure from a 1-D MARCS model atmosphere which uses amixing-length approximation for convective flux transport. Our directfits to the interferometric data confirm this prediction, however wefind that not all 1-D models fail to reproduce the observations. The keyto matching the interferometric data is a shallower temperature gradientthan provided by the standard 1-D mixing-length approximation. We findthat in addition to our best fitting 3-D hydrodynamical model, a 1-DATLAS12 model, with an additional free parameter for ``approximateovershooting'', provides the required temperature gradient. We estimatethat an interferometric precision better than 0.1% will be required todistinguish between the 3-D model and the ATLAS12 model. Thisovershooting approximation has been shown to match Solar limb-darkeningobservations reasonably well (Castelli et al 1997 A&A 324, 432), howeverpublished work since using Strömgren photometry of solar-type starshas cast doubt on the importance of overshooting. We have also comparedsynthetic spectral energy distributions for Procyon to ultraviolet,optical and near-infrared spectrophotometry and find differences fromcomparisons to Strömgren photometry alone.This work was performed in part contract with the Jet PropulsionLaboratory (JPL) funded by NASA through the Michelson FellowshipProgram. JPL is managed for NASA by the California Institute ofTechnology.

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NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

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