Indirect evidence for short period magnetic cycles in W UMa stars

Abstract

Complex period variations of five W UMa type binaries (AB And, OO Aql, DK Cyg, V566 Oph, U Peg) were investigated by analyzing their O−C diagrams, and several common features were found. Four of the five systems show secular period variations at a constant rate on the order of |Ṗ sec /P| ∼ 10 −7 yr −1 . In the case of AB And, OO Aql, and U Peg a high-amplitude, nearly one-century long quasi-sinusoidal pattern was also found. It might be explained as light-time effect, or by some magnetic phenomena, although the mathematical, and consequently the physical, parameters of these fits are very problematic, as the obtained periods are very close to the length of the total data range. The most interesting feature of the studied O−C diagrams is a low amplitude (∼2−4 × 10 −3 d) modulation with a period around 18-20 yr in four of the five cases. This phenomenon might be indirect evidence of some magnetic cycle in late-type overcontact binaries as an analog to the observed activity cycles in RS CVn systems.

Physical parameters and multiplicity of five southern close eclipsing binaries

“…The Fourier spectrum of the residuals shows that the highest peak has an S/N ratio (Breger et al 1993) of 3, thus its significance is marginal. Nevertheless, the corresponding modulation period (∼5100 d or 14 yr) and amplitude (0.0016 d) are very similar to those found by Borkovits et al (2005) for AB And, OO Aql, V566 Oph and U Peg. We therefore conclude that XY Leo is likely to bear signatures of short-period magnetic cycles in W UMa-type variables, but several years of further continuous eclipse timings are needed to improve the significance of the detection.…”

“…An analysis of the long-term period change of the triple W UMa VW Cep revealed secondary cycles in the O−C diagram that were interpreted as possible evidence of magnetic activity (Kaszás et al 1998). More recently, Borkovits et al (2005) investigated complex period variations of five W UMa-type binaries, finding some common features. These include secular period variation at a constant rate and a low-amplitude modulation with periods around 18-20 yr in four of the five cases.…”

Characterization of 9380 contact binaries from the CRTS Variable Sources Catalogue

“…If the Applegate mechanism is indeed responsible for the luminosity variation, this study would add to the evidence for short period magnetic activity cycles on W UMa stars (Kaszás et al 1998;Shengbang & Qingyao 2000;Lee et al 2004;Zhang & Zhang 2004;Borkovits et al 2005;Qian et al 2007;Yang, Qian & Soonthornthum 2012).…”

THE BERLIN EXOPLANET SEARCH TELESCOPE II CATALOG OF VARIABLE STARS. II. CHARACTERIZATION OF THE CoRoT SRc02 FIELD

“…In case of contact binaries, long-timescale magnetic cycles (10-20 years, e.g., Borkaovits et al 2005), spot-induced eclipse timing variations (Tran et al 2013), effect of mass transfer, third bodies, and irregular variations occur (Qian 2001a(Qian , 2001b(Qian , 2003Borkovits et al 2005;Tran et al 2013;Nelson et al 2014). Since this target is bright even for small telescopes, it is a good target for such period variation studies.…”