We solve new UBV light curves of the eclipsing binary CN Andromedae simultaneously with radial velocities by the method of differential corrections. We find it semidetached with the more massive star filling its limiting lobe and the less massive star very close to lobe-filling. Our solutions of earlier light curves have the same configuration. Within the uncertainties, the system may be in a broken or a marginal contact stage as it undergoes thermal relaxation oscillations. The light curves are strongly affected by a large dark spot at high latitude on the more massive star and by a bright substellar spot on the companion. Spot locations and temperatures do not differ significantly from epoch to epoch. Based on single star evolutionary models, the primary's mass (1.299 ± 0.045 M⊙) and radius (1.425 ± 0.016 R⊙) are consistent with those of a star of age 2.9 × 109 yr that will leave the main sequence in another 2.0 × 109 yr. The orbital period has decreased during the past 50 yr according to traditional eclipse timings and also according to our generalized light and velocity solutions that include a reference epoch T0 and a rate of period change dP/dt. We find dP/dt = -0.01951 ± 0.00054 s yr-1, which is consistent with mass transfer from the more to the less massive star of 1.4 × 10-7 M⊙ yr-1, assuming no mass is lost from the system. Reliable absolute dimensions are determined.

https://iopscience.iop.org/article/10.1086/324110/pdf

CN Andromedae: A Broken-Contact Binary?

A photoelectric light curve of BL And is presented along with the first CCD light curve of GW Tau. Both objects are short-period eclipsing binaries and were observed in 2003 or 2004. Photometric elements were computed using the latest version of the Wilson-Van Hamme code. The results reveal that BL And is a semidetached system with the primary component filling its Roche lobe and the secondary one almost filling but still detached, while GW Tau is a marginal-contact binary system with a small degree of contact (f= 10.9 per cent) and a large temperature difference of about 3100 K. All available eclipse times, including new ones, were analysed for each system. It was found that the orbital period of BL And is decreasing at the rate of dP/dt=-2.36 x 10(-8) (+/- 0.09) d yr(-1) while that of GW Tau may be decreasing or oscillating. We think period decrease is more probable. The derived configuration and secular period decrease for BL And combined with the asymmetry of the light curve indicate that this system may evolve from the present semidetached phase into a contact stage, with mass transfer from the primary component to the secondary one through the L-1 point, or that it might just undergo the broken stage predicted by the theory of thermal relaxation oscillations. In contrast, GW Tau is a marginal-contact binary in poor thermal contact and may be at the beginning of the contact phase.

BL andromedae and GW Tauri : close binary stars in a key evolutionary stage

A detailed period study of the short-period (P = 0.(d)58) close binary system, BO Peg, is presented based on the analysis of its O-C curve. It is found that the orbital period shows a continuous decrease with a rate dP/dt = -1.26 x 10(-7) days/year while it undergoes a possible small-amplitude oscillation. If the period oscillation is cyclic, it can be explained either by the light-time effect via the presence of an unseen third body or by the magnetic activity cycle of the secondary component. The continuous period decrease suggests a secular mass transfer from the more massive to the less massive component, which is in agreement with the near-contact configuration with a lobe-filling primary (Yamasaki & Okazaki 1986). These observations, as seen in RT Scl, FT Lup, TT Her, RS Ind, and V388 Cyg, are consistent with the Thermal Relaxation Oscillation (TRO) theory in that the primary component is transferring mass to the secondary in the broken-contact phase. To satisfy such a decrease in the orbital period, a conservative mass transfer rate (with no magnetic effect) would be of the order of dM/dt = 1.53 x 10(-7) M./year.

/pdf/bo-pegasi-a-candidate-on-the-breaking-stage-of-the-tro-cycle-51ilm97h64.pdf

BO Pegasi: A candidate on the breaking stage of the TRO cycle

We present BVR full-light curves of V388 Cyg to provide a complete photometric solution for the first time. The light curves show a high degree of asymmetry (O'Connell effect). The maxima at 0.25 phase (Max I) are 0.023, 0.018 and 0.012 mag higher than those at 0.75 phase (Max II) in B, V and R, respectively. Three possible spot models are applied to fit the asymmetric light curves of V388 Cyg, in order to explain the O'Connell effect. We conclude that the model of the cool spot on the cooler star is the most reasonable model for V388 Cyg. The continuous period variation is confirmed by recently collected times of minima, including one minimum that is determined in this paper. The period decrease rate is estimated as dp/dt=−2.055×10−7 d yr−1.

/pdf/charge-coupled-device-observations-of-v388-cyg-34lrt95uz8.pdf

Charge-coupled device observations of V388 Cyg

First multi-color photometric study and preliminary elements for the low-mass ratio, possible progenitors of merging stars, W UMa systems TYC 3836-0854-1 and TYC 4157-0683-1

L. Milano

Papers

V388 Cygni: a binary system in the rapid phase of mass exchange?