Amplitude and frequency variations of oscillation modes in the pulsating DB white dwarf star KIC 08626021 - The likely signature of nonlinear resonant mode couplingW. Zong, S. Charpinet, G. Vauclair, N. Giammichele and V. Van GrootelA&A, 585 (2016) A22DOI: https://doi.org/10.1051/0004-6361/201526300