Letter to the Editor

QPOs in cataclysmic variables and in X-ray binaries

¹ Nordita, Blegdamsvej 17, 2100 Copenhagen, Denmark e-mail: lasota@iap.fr
² Institute of Astronomy, Univ. of Zielona Góra, ul. Lubuska 2, 65-265 Zielona Góra, Poland
³ Copernicus Astronomical Center, ul. Bartycka 18, 00-716 Warszawa, Poland
⁴ Institut d'Astrophysique de Paris, UMR 7095 CNRS, Univ. P. & M. Curie, 98bis Bd. Arago, 75014 Paris, France
⁵ Department of Astrophysics, Göteborg University, Göteborg, Sweden
⁶ Department of Astronomy, University of Cape Town, Rondebosch 7700, South Africa

Received: 4 May 2005
Accepted: 29 July 2005

Abstract

Recent observations, reported by Warner and Woudt, of Dwarf Nova Oscillations (DNOs) exhibiting frequency drift, period doubling, and 1:2:3 harmonic structure, can be understood as disc oscillations that are excited by perturbations at the spin frequency of the white dwarf or of its equatorial layers. Similar quasi-periodic disc oscillations in black hole low-mass X-ray binary (LMXB) transients in a 2:3 frequency ratio show no evidence of frequency drift and correspond to two separate modes of disc oscillation excited by an internal resonance. Just as no effects of general relativity play a role in white dwarf DNOs, no stellar surface or magnetic field effects need be invoked to explain the black hole QPOs.