Dwarf Nova EZ Lyncis Second Visit to Instability Strip

Abstract: The analysis of 14 periodograms of EZ Lyn for the data spaced over 565 d in 2012--2014 (2-3.5 yr after 2010 outburst) yielded the existence of the stable signals around 100 c/d and three signals around 310 c/d, 338 c/d and 368 c/d (the corresponding periods are 864 s, 279 s, 256 s and 235 s). We interpret them as independent non-radial pulsations of the white dwarf in EZ Lyn, but a possibility that a linear combination of frequency at 100 c/d and harmonic of orbital period could produce the frequency at 368 c/d also cannot be excluded. The signal at 100 c/d was detected during the first stay in the instability strip as a transient one. The period at 338 c/d, is a known non-radial pulsation EZ Lyn entered the instability strip after the 2010 outburst. We detected the signals around 310 c/d and 368 c/d for the first time. We applied the two-dimensional least absolute shrinkage and selection operator (Lasso) analysis for the first time to explore the behavior of these signals on the scale of hours for nightly runs of observations having duration of 6-12 hr. The Lasso analysis revealed the simultaneous existence of all three frequencies (310 c/d, 338 c/d and 368 c/d) for majority of nights of observations, but with variable amplitudes and variable drifts of frequencies by 2-6 percents on a time scale of ~5-7 hr. The largest drift we detected corresponded to 17.5 s in period in ~5 hours.