Abstract

From 1999-2002 photometric observations of the old nova RW UMi (1956), we systematically detect a dominant modulation with a period P0 peaking in the range 1.7-2.4 hr. This period, on average, is about 45% longer than the previously suggested orbital period of ?1.42 hr. This could be due to the occasional presence of low-frequency quasi-periodic oscillations (QPOs) that can eventually dominate the light curve. Rather irregular QPOs, on the order of the orbital period, can be produced by vertical oscillations of the inner-disk region excited by the rotating magnetosphere of the white dwarf. Thus, RW UMi could be an intermediate polar system. Since we find that the luminosity of the postnova is decaying at a rate of ?0.02 mag yr-1, we should observe some important changes in its photometric behavior in the future.