  In this paper we revisit the arguments for the basis of the time evolution of
the flares expected to arise when a star is disrupted by a supermassive black
hole. We present a simple analytic model relating the lightcurve to the
internal density structure of the star. We thus show that the standard
lightcurve proportional to $t^{-5/3}$ only holds at late times. Close to the
peak luminosity the lightcurve is shallower, deviating more strongly from
$t^{-5/3}$ for more centrally concentrated (e.g. solar--type) stars. We test
our model numerically by simulating the tidal disruption of several stellar
models, described by simple polytropic spheres with index $\gamma$. The
simulations agree with the analytical model given two considerations. First,
the stars are somewhat inflated on reaching pericentre because of the effective
reduction of gravity in the tidal field of the black hole. This is well
described by a homologous expansion by a factor which becomes smaller as the
polytropic index becomes larger. Second, for large polytropic indices wings
appear in the tails of the energy distribution, indicating that some material
is pushed further away from parabolic orbits by shocks in the tidal tails. In
all our simulations, the $t^{-5/3}$ lightcurve is achieved only at late stages.
In particular we predict that for solar type stars, this happens only after the
luminosity has dropped by at least two magnitudes from the peak. We discuss our
results in the light of recent observations of flares in otherwise quiescent
galaxies and note the dependence of these results on further parameters, such
as the star/hole mass ratio and the stellar orbit.
