Ryoko Ishioka — Page 2

arXiv2001

First detection of the growing humps at the rapidly rising stage of dwarf novae AL Com and WZ Sge

We report on time-series photometric observations in the earliest stages of superoutbursts of the extreme dwarf novae, AL Com and WZ Sge, which started on 2001 May after the 6 years quiescence and on 2001 July after the 23 years quiescence, respectively. We detected growth of ``early superhumps'' during the each rising stage. Our observations reject the mass transfer instability for the trigger of the superoutburst of WZ Sge stars, and show the existence of some relations between the ``early superhumps'' and the spiral structure, which give a hint of the origin of the ``early superhumps.''

astro-ph↗

arXiv2001

Large-Amplitude 2.65-d Oscillation in the VY Scl-Type star V425 Cas

From long-term photometry of a VY Scl-type star, V425 Cas, between 1998 and 2000, we discovered a short-term, large-amplitude (up to 1.5 mag) variations. The variation was well represented by a single period of 2.65 d. The large amplitude and the profile of the folded light curve suggest that the dwarf nova-type disk instability is responsible for this variation. The shortness of the period is unprecedented in hydrogen-rich cataclysmic variables. Given the recent emerging evidence that the irradiation from white dwarfs in VY Scl-type systems affect their light behavior, we propose a possibility that this unique variation in V425 Cas can be explained by the combination of the dwarf nova-type disk instability and irradiation. Similar short-period "outbursts" have been known in X-ray transients (V518 Per), and helium cataclysmic variables (CR Boo and V803 Cen). We discuss the possibility that these phenomena have a common origin to the unique variation in V425 Cas.

astro-ph↗