2007PASP..119..393Z

An empirical linear relation is found to exist between the high and low frequencies (ν_high, ν_low) of quasi-periodic oscillations (QPOs) for black hole candidates (BHCs), neutron stars (NSs), and white dwarfs (WDs) in binary systems, spanning 5 orders of magnitude in frequency. For the NS Z (atoll) sources, ν_high and ν_loware identified as the lower kHz QPO frequency and horizontal-branch oscillation (HBO) frequency ν_HBO (broad noise components); for the BHCs and low-luminosity NSs, they are the QPOs and broad noise components at frequencies between 1 and 10 Hz; for WDs, they are the ``dwarf nova oscillations'' (DNOs) and QPOs of cataclysmic variables (CVs). To interpret this relation, our model ascribes ν_high to the Alfvén wave oscillation frequency at a preferred radius, and ν_low to the same mechanism at another radius. We can then obtain ν_low=0.08ν_high and the relation between the upper kHz QPO frequency ν₂ and the HBO frequency, ν_HBO≃(56 Hz)(ν₂/kHz)², which are in accordance with the observed empirical relations. Furthermore, some implications of the model are discussed, including why QPO frequencies of WDs and NSs span 5 orders of magnitude.