  Context. Abundance anomalies observed in a fraction of A and B stars of both
Pop I and II are apparently related to internal particle transport. Aims. Using
available constraints from Sirius A, we wish to determine how well evolutionary
models including atomic diffusion can explain observed abundance anomalies when
either turbulence or mass loss is used as the main competitor to atomic
diffusion. Methods. Complete stellar evolution models, including the effects of
atomic diffusion and radiative accelerations, have been computed from the zero
age main-sequence of 2.1M\odot stars for metallicities of Z0 = 0.01 \pm 0.001
and shown to agree with the observed parameters of Sirius A. Surface abundances
were predicted for three values of the mass loss rate and for four values of
the mixed surface zone. Results. A mixed mass of ~ 10^-6 M\odot or a mass loss
rate of 10^-13 M\odot/yr were determined through comparison with observations.
Of the 17 abundances determined observationally which are included in our
calculations, up to 15 can be predicted within 2 sigmas and 3 of the 4
determined upper limits are compatible. Conclusions. While the abundance
anomalies can be reproduced slightly better using turbulence as the process
competing with atomic diffusion, mass loss probably ought to be preferred since
the mass loss rate required to fit abundance anomalies is compatible with the
observationally determined rate. A mass loss rate within a factor of 2 of
10^-13 M\odot/yr is preferred. This restricts the range of the directly
observed mass loss rate.
