NGC 6240: A triple nucleus system in the advanced or final state of mergingW. Kollatschny, P. M. Weilbacher, M. W. Ochmann, D. Chelouche, A. Monreal-Ibero, R. Bacon and T. ContiniA&A, 633 (2020) A79DOI: https://doi.org/10.1051/0004-6361/201936540