Transient emission of selected CRTS Cataclysmic Variables

We present optical photometric and spectroscopic observations of three SU UMa-type dwarf novae, i.e. AR Pic, QW Ser and V521 Peg, conducted in 2016 and 2017. These sources were selected from the Catalina Real-Time Transient Survey and observed during quiescence, outburst (AR Pic and QW Ser) and superoutburst (V521 Peg). For AR Pic, strong flickering in the light curves and an asymmetric double-peaked H$\beta$ emission line in the spectra, confirmed the presence of a very active hot spot. During outburst, detected on 18 February 2017, it exhibited a $\sim 3.3$ magnitude brightening. The projected velocity of the inner edge of the accretion disc is $\sim 2000 \rm~km~s^{-1}$. An outburst of QW Ser was detected on 8 August 2016. Absorption lines, characteristic of an optically thick disc during outburst, were detected and an outflow velocity of $\sim 1000 \rm ~km~s^{-1}$ was determined. Optical spectra during the superoutburst of V521 Peg were obtained for the first time, confirming the superoutburst nature of the outburst, as also observed in other SU UMa-type dwarf novae. The superoutburst was detected on 1 September 2017. Well-defined superhumps were observed, with an average superhump period of $P_{\rm sh} \sim 1.48$ hr. A mass ratio of $q \sim 0.14$ was determined from the period excess of $\varepsilon \sim 3 \%$.