Signatures of Convection in the Spectrum of Procyon: Fundamental Parameters and Iron Abundance

We have observed the spectrum of Procyon A (F5IV) from 4559 to 5780 A with aS/N of ~ 1e3 and a resolving power of 2e5. We have measured the line bisectorsand relative line shifts of a large number of Fe I and Fe II lines, comparingthem to those found in the Sun. A three-dimensional(3D) hydrodynamical modelatmosphere has been computed and is tested against observations. The modelreproduces in detail most of the features observed, although we identify someroom for improvement. At all levels, the comparison of the 3D time-dependentcalculations with the observed spectral lines shows a much better agreementthan for classical homogeneous models, making it possible to refine previousestimates of the iron abundance, the projected rotational velocity, thelimb-darkening, and the systemic velocity of the Procyon binary system. The difference between the iron abundance determined with the 3D model andits 1D counterpart is <~ 0.05 dex. We find consistency between the iron abundancederived from Fe I and Fe II lines, suggesting that departures from LTE in theformation of the studied lines are relatively small. The scatter in the ironabundance determined from different lines still exceeds the expectations fromthe uncertainties in the atomic data, pointing out that one or more componentsin the modeling can be refined further.Comment: 30 pages, 19 figures; uses emulateapj.sty (included); to appear in ApJ (Feb 2002