tokens: WD resulting from the merger of two equal-mass WDs by assuming the extreme situation of complete mixing between the two WDs and a CO core for the merged remnant. To this end, we adopted the internal distribution of carbon, oxygen, and He of the 0.58 M ⊙ WD model computed in Miller Bertolami (2016) from the evolutionary history of its progenitor star. Assuming complete mixing between both WDs, the mass fraction of He, carbon and oxygen throughout the interior of our UMCO WD model results X He = 0.017, X C = 0.363 and X O = 0.62. We mention that in this study we are interested in the advanced evolutionary stages of the WD and not the evolutionary stages shortly after the merger event, which cannot be adequately followed by our stellar evolution code. Finally, in this work we did not consider the possibility that WD mergers lead to ultra-massive ONe-core WDs, as predicted in Schwab (2021) . The reason is that we do not expect such ONe WDs to present marked differences in their pulsational properties as compared with the ONe-core models resulting from the single evolution that is explored in the present paper. 4. Evolutionary properties In this section, we compare the evolutionary properties of our UMCO WD models resulting from the two single-evolution scenarios and from the binary merger we described previously, with those predicted by the ONe-core WD models resulting from off-centre carbon burning during the single evolution of the progenitor star ( Siess 2010 ). To isolate the impact of the internal composition predicted by the possible scenarios, we adopted the same stellar mass of 1.159 M ⊙ for all of our WD sequences 4 . In addition, we assumed the same H content for all of our sequences except the merger case. In particular, it was taken as nearly the maximum allowed by evolutionary considerations for such stellar mass, log( M H / M ⋆ )≈ − 6. This limit is imposed by the occurrence of unstable nuclear burning on the cooling track for the WD mass considered. Finally, the ONe-core WD-evolutionary and -pulsational models were taken from Camisassa et al. (2019) and De Gerónimo et al. (2019) . Such models were computed with the same codes we used to compute the evolution and pulsations of our UMCO WD models (see Sect. 2 for details). The evolutions of all of our WD sequences were followed from very high luminosities, through the domain of the pulsating ZZ Ceti stars, down to very low surface luminosities. In Fig. 5 , we display the internal chemical profile of our UMCO WD models (see Sect. 3 for details), together with the chemical profile of the ONe-core WD model studied in Camisassa et al. (2019) , top panel. Specifically, the second and third panels illustrate, respectively, the chemical profiles resulting from reducing the mass-loss rates of an initially 7.8 M ⊙ progenitor star, and those from considering core rotation ( f = 0.1) in the AGB phase of an initially 7.6 M ⊙ progenitor star. The bottom panel shows the chemical profile we
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