Conjugacy separability of certain HNN extensions with normal associated subgroups

In this paper‎, ‎we will give necessary and sufficient conditions for certain HNN extensions of‎ ‎subgroup separable groups with normal associated subgroup to be conjugacy separable‎. ‎In fact‎, ‎we will show that these HNN extensions are conjugacy separable if and only if the normalizer of one of its associated subgroup is conjugacy separable‎..