Solar-type cycles of the secondary stars in cataclysmic variables

Abstract

We found cyclical variations in the quiescent magnitudes and outburst intervals of 21 dwarf novae, 1 nova and 1 nova-like star produced by the solar-type cycles of the late-type secondary components. More than 70% of individual systems in this work are first studied by Fourier periodogram analysis. It seems that the mean cycle amplitudes of the quiescent magnitudes are considerably larger for SU UMa stars. Cyclical modulations of quiescent magnitudes found for the stars, which have orbital periods below the period gap, support the hypothesis that even almost fully convective secondaries may possess activity cycles. The estimated probability density functions show peaks at 9.7, 7.9 and 8.6 yrs for cataclysmic variables (CVs), single main-sequence stars (MS) and all stars (CVs+MS), respectively. Using a larger set of data, we confirm that there is no correlation of the cycle period with the rotational regime of the secondary star. It is also confirmed that cycle periods of CVs are in the range of those of single main-sequence stars. We note that the observational cycle parameters (i.e. cycle period, Pcyc, and cycle amplitude of quiescent magnitudes, ∆m) do not seem in relation with any other parameter such as masses of primary and secondary stars, mean outburst interval, mean outburst duration, mean decline and rise rate of outbursts, absolute magnitudes in quiescent and outburst states etc.

DQ Herculis in Profile: Whole Earth Telescope Observations and Smoothed Particle Hydrodynamics Simulations of an Edge‐on Cataclysmic Variable System

“…The period of these variations and similar variations in the orbital periods of other cataclysmic variables might have its origin in magnetic activity cycles on the secondary star analogous to the 11 yr solar cycle (Applegate & Patterson 1987;Warner 1988;Ak et al 2001;Baptista et al 2003). When the Zhang et al, WET, and SARA data are included, a sine fit is still formally significant, but not compelling Starting with the fractional amplitude light curves described above, we clipped out data from orbital phases 0.91 to 0.09 to remove the eclipse-related phase shifts.…”

Do spherical $\mathsf{\alpha}^2$-dynamos oscillate?

“…The fully convective donating stars in short-period cataclysmic variables are suspected to act as α 2 -dynamos with magnetic poles slowly migrating along the equator (Hessman 2003). Ak et al (2001) report solar-type cycles for the same class of stars. Together with the highly nonaxisymmetric field configurations for very young cool dwarf stars reported by Jardine et al (2002, see Fig.…”

Roche tomography of cataclysmic variables - V. A high-latitude starspot on RU Pegasi

“…Magnetic activity cycles have also been cited as possible causes for a number of other observed CV phenomena, such as variations in orbital periods, luminosity, mean outburst durations and outburst shapes (e.g. Applegate 1992; Richman, Applegate & Patterson 1994; Ak, Ozkan & Mattei 2001). Given the importance of understanding the underlying magnetic properties of these stars, it is therefore highly desirable to try to obtain observational evidence for such fields, in the form of the sizes, distributions and lifetimes of starspots.…”