A CRUCIAL TEST OF THE DIFFUSION-MODEL - 53-CAMELOPARDALIS

Observations of 53 Cam determine the magnetic and atmospheric parameters of this star. Using these observed parameters, radiative accelerations were calculated for Ca, Sc, Ti, Mn, Cr, and Sr in the atmosphere. Taking the magnetic field into account, expected abundance anomalies were then calculated and compared with the recent observations of Landstreet for this star. In the absence of mass loss, meridional circulation, and turbulence, diffusion dominates particle transport and leads to what we call the simple diffusion model. It is nearly uniquely determined by observations. The only uncertainty is the state of the hydrogen convection zone. It is suppressed totally or partially by the magnetic field? Assuming that the convection zone is only partially suppressed, we show that the simple diffusion model can account for the averaged observed abundance anomalies. Whatever the assumption made on the effect of the magnetic field on convection, it is shown, however, that the simple diffusion model cannot explain the observed time dependence and thus the observed geographic distribution of the abundance anomalies. There are well-established abundance anomalies whose time dependence is impossible to explain within the simple model based on diffusion. It is described how a mass-loss rate between 10(-4) and 10(-12) M. yr-1 could lead to the observed time dependence. It is suggested that observations of other elements, in particular of rare earths, would be important in further constraining the model.