Does the Wolf-Rayet binary CQ Cephei undergo sporadic mass transfer events?

Abstract

Context. Stellar wind mass-loss in binary systems carries away angular momentum causing a monotonic increase in the orbital period, P > 0. Despite possessing a significant stellar wind, the eclipsing Wolf-Rayet (WR) binary system CQ Cep does not show the expected monotonic period increase, in fact, it is sometimes reported to display the opposite behavior. Aims. The objective of this paper is to perform a new analysis of the rate of period changeṖ and determine the conditions under which Roche-lobe overflow (RLO) mass-transfer combined with wind mass loss can explain the discrepant behavior. Methods. The historic records of times of light curve minima were reviewed and compared with the theoretical values ofṖ for cases in which both wind mass-loss and RLO occur simultaneously. Results. The observational data indicate thatṖ alternates between positive and negative values on a timescale of years. The negative values (Ṗ ∼ −0.6 to −8.5 s yr −1 ) are significantly larger in absolute value than the positive ones (Ṗ ∼ +0.2 to +1.2 s yr −1 ). We find that a plausible scenario for CQ Cep is one in which the O star undergoes intense but sporadic RLO events that lead to accretion onto the WR star, at which timesṖ < 0. At other times,Ṗ > 0 when the WR wind, and possibly material swept up from the O star, carries angular momentum away from the system. A scenario in which the WR star is the mass donor cannot be excluded, but requires that either the WR wind mass-loss rate undergoes large sporadic enhancements or that an additional process that removes angular momentum from the system be present.

A Multiwavelength Search for Intrinsic Linear Polarization in Wolf–Rayet Winds

“…WR 155 is an extremely short-period WN6o + O9II-Ib system, which undergoes sporadic periods of Roche lobe overflow, transferring mass between the O and WR stars Koenigsberger et al (2017). It is likely that the intrinsic polarization is caused by asymmetric wind structures produced due to these interactions between the stars.…”

High energy processes in Wolf‐Rayet stars

“…The times of minimum ACA optical brightness at ϕ = 0 in 2013 and 2017 give an accurate orbital period P = 1.641239 (±8.0e−07) days. Analysis of historical data suggests that the period may be variable (Koenigsberger et al ).…”