Periodic modulations during a long outburst in V363 Lyr

Abstract

I analyzed the Kepler long and short cadence data of V363 Lyr. A period of 0.185723(8) d was persistently detected and this is identified as the orbital period. V363 Lyr showed one long outburst accompanied by an "(embedded) precursor" during Kepler observations and modulations with a period of 0.1956(2) d, longer than the orbital one, were detected during this outburst. There are two possible interpretations of this period. The first one is superhumps despite that V363 Lyr is far above the period gap. This interpretation requires an evolved, undermassive secondary enabling a low mass ratio of q=0.15. The evolution of this long-period variations, however, does not follow the standard evolution of superhumps. The second one is that the precursor occurred when the disk reached the tidal truncation radius, as inferred from observations of IW And stars. In this case, the long-period variations could be interpreted as a variable stream impact on a precessing eccentric disk, which may have been formed by disturbances at the tidal truncation radius. This might lead to effective removal of the angular momentum which resulted in 0.3-0.4 mag brightening following the precursor. The fractional period excess suggests that q is just above the stability limit of the 3:1 resonance. In either cases, the nature of the secondary and the mass ratio need to be verified by spectroscopic observations.