Monitoring the late decline of the old nova RW Ursae Minoris

¹ Department of Astronomy, University of Padova, vicolo dell'Osservatorio 2, 35122 Padova, Italy e-mail: antonio.bianchini@unipd.it
² Department of Physics and Astronomy, University of Wyoming, Laramie, WY 82071, USA

Received: 7 November 2006
Accepted: 18 December 2006

Abstract

New 2003–2006 time-resolved photometric observations of the old nova RW UMi (1956) confirm the QPO nature of the light modulations observed. The analysis of all our historical runs show that QPOs tend to cluster around frequencies 4.96 d^-1 and 12.4 d^-1 while the historical superhump period remains undetected in our data. Although the two main frequencies observed might appear to be aliases of the superhump frequency 17 d^-1, they should be produced by two independent mechanisms. These rather irregular QPOs might be explained by vertical oscillations of the inner regions of the accretion disk and/or by the cyclical generation in the disk of travelling density waves at the co-rotation radius of an inclined magnetic rotator. We find that the post-nova luminosity is decaying at a rate of ~0.03 mag y^-1. If RW UMi is an intermediate polar system, during the decline the magnetospheric radius of the accreting white dwarf primary should increase and produce important changes in the periods of QPOs.