  We infer from different seismic observations the energy supplied per unit of
time by turbulent convection to the acoustic modes of Alpha Cen A (HD 128620),
a star which is similar but not identical to the Sun. The inferred rates of
energy supplied to the modes (i.e. mode excitation rates) are found to be
significantly larger than in the Sun. They are compared with those computed
with an excitation model that includes two sources of driving, the Reynolds
stress contribution and the advection of entropy fluctuations. The model also
uses a closure model, the Closure Model with Plumes (CMP hereafter), that takes
the asymmetry between the up- and down-flows (i.e. the granules and plumes,
respectively) into account. Different prescriptions for the eddy-time
correlation function are also confronted to observational data. Calculations
based on a Gaussian eddy-time correlation underestimate excitation rates
compared with the values derived from observations for Alpha Cen A. On the
other hand, calculations based on a Lorentzian eddy-time correlation lie within
the observational error bars. This confirms results obtained in the solar case.
With respect to the helioseismic data, those obtained for Alpha Cen A
constitute an additional support for our model of excitation. We show that mode
masses must be computed taking turbulent pressure into account. Finally, we
emphasize the need for more accurate seismic measurements in order to
discriminate, in the case of Alpha Cen A, between the CMP closure model and the
quasi-Normal Approximation as well as to confirm or not the need to include the
excitation by the entropy fluctuations.

Astrophysics