  In this paper we investigate via an asymptotic method the opening of gaps in
the spectrum of a stiff problem for the Laplace operator $-\Delta$ in
$\mathbb{R}^2$ perforated by contiguous circular holes. The density and the
stiffness constants are of order $\varepsilon^{-2m}$ and $\varepsilon^{-1}$ in
the holes with $m\in (0,1/2)$. We provide an explicit expression of the leading
terms of the eigenvalues and the corresponding eigenfunctions which are related
to the Bessel functions of the first kind.
