The limiting spectrum of a non-self-conjugate second-order differential operator with slowly varying coefficients

We describe the limiting spectrum $C(L)$ of the non-self-conjugate second-order differential operator $L$ with slowly varying coefficients, defined in $L^2(-\infty,\infty)$. The limiting spectrum is constructed from the spectra of operators with constant coefficients which are obtained from $L$ by “freezingrd”; the argument in the variable coefficients.