Predicting the Future of Superhumps in Classical Nova Systems

Oscillations observed in the light curve of Nova V1974 Cygni 1992 since summer 1994 have been interpreted as permanent superhumps. From simple calculations based on the Tidal-Disk Instability model of Osaki, and assuming that the accretion disc is the dominant optical source in the binary system, we predict that the nova will evolve to become an SU UMa system as its brightness declines from its present luminosity by another 2-3 magnitudes. Linear extrapolation of its current rate of fading (in magnitude units) puts the time of this phase transition within the next 2-4 years. Alternatively, the brightness decline will stop before the nova reaches that level, and the system will continue to show permanent superhumps in its light curve. It will then be similar to two other old novae, V603 Aql and CP Pup, that still display the permanent superhumps phenomenon 79 and 55 years, respectively, after their eruptions. We suggest that non-magnetic novae with short orbital periods could be progenitors of permanent superhump systems.Comment: 5 pages, 2 eps. figures, Latex, accepted for publication in MNRA

Nova V1425 Aquilae 1995 - The Early Appearance of Accretion Processes in An Intermediate Polar Candidate

Continuous CCD photometry of Nova Aquilae 1995 was performed through the standard B,V,R and I filters during three nights in 1995 and with the I filter during 18 nights in 1996. The power spectrum of the 1996 data reveals three periodicities in the light curve: 0.2558 d, 0.06005 d and 0.079 d, with peak-to-peak amplitudes of about 0.012, 0.014 and 0.007 mag. respectively. The two shorter periods are absent from the power spectrum of the 1995 light curve, while the long one is probably already present in the light curve of that year. We propose that V1425 Aql should be classified as an Intermediate - Polar CV. Accordingly the three periods are interpreted as the orbital period of the underlying binary system, the spin period of the magnetic white dwarf and the beat period between them. Our results suggest that no later than 15 months after the outburst of the nova, accretion processes are taking place in this stellar system. Matter is being transferred from the cool component, most likely through an accretion disc and via accretion columns on to the magnetic poles of the hot component.Comment: 7 pages, 4 eps. figures, Latex, accepted for publication in MNRA

Discovery of the 1.80 hr Spin Period of the White Dwarf of the Symbiotic System BF Cyg

We report on the discovery of a coherent periodicity in the B light curve of the symbiotic star BF Cyg. The signal was detected in some sections of the light curve of the star recorded in the year 2003 as double hump periodic variations with an amplitude of ~7 mmag. In the year 2004 the signal was also present in only a subsection of the light curve. In that year, the system was about twice as bright and the amplitude of the oscillations was about half of what it was in 2003. In 2004 the cycle structure was of a single hump, the phase of which coincided with the phase of one of the humps in the 2003 cycle. No periodic signal was detected in a third, short series of observations performed in the year 2007, when the star was three magnitudes brighter than in 2003. We interpret the periodicity as the spin period of the white dwarf component of this interacting binary system. We suggest that the signal in 2003 originated in two hot spots on or near the surface of the white dwarf, most likely around the two antipodes of an oblique dipole magnetic field of this star. Magnetic field lines funneled accreted matter from the wind of the cool component to the pole areas, where the falling material created the hot spots. This process is apparently intermittent in its nature. In 2004, the activity near only one pole was enhanced enough to raise the signal above the threshold of our detection ability.Comment: 7 pages, 5 figures, accepted for publication in MNRA