  This work is devoted to study the asymptotic behavior of critical points
$\{(u_\varepsilon,v_\varepsilon)\}_{\varepsilon>0}$ of the Ambrosio-Tortorelli
functional. Under a uniform energy bound assumption, the usual
$\Gamma$-convergence theory ensures that $(u_\varepsilon,v_\varepsilon)$
converges in the $L^2$-sense to some $(u_*,1)$ as $\varepsilon\to 0$, where
$u_*$ is a special function of bounded variation. Assuming further the
Ambrosio-Tortorelli energy of $(u_\varepsilon,v_\varepsilon)$ to converge to
the Mumford-Shah energy of $u_*$, the later is shown to be a critical point
with respect to inner variations of the Mumford-Shah functional. As a
byproduct, the second inner variation is also shown to pass to the limit. To
establish these convergence results, interior ($\mathscr{C}^\infty$) regularity
and boundary regularity for Dirichlet boundary conditions are first obtained
for a fixed parameter $\varepsilon>0$. The asymptotic analysis is then
performed by means of varifold theory in the spirit of scalar phase transition
problems.
