No 0.1-d period in V2491 Cyg https://ui.adsabs.harvard.edu/abs/2011A%26A...530A..70D/abstract "On the progenitor system of Nova V2491 Cygni" No such period was detected in the ZTF data. Two time-resolved runs in the ZTF data did not show any sign of such a period. The detection by this paper was probably spurious. There was no sign of the reported possible spin period (see Zemko et al. 2015).