Physical parameters of close binary systems: VIII

Abstract

This paper presents the results of a combined spectroscopic and photometric study of 20 contact binary systems: HV Aqr, OO Aql, FI Boo, TX Cnc, OT Cnc, EE Cet, RW Com, KR Com, V401 Cyg, V345 Gem, AK Her, V502 Oph, V566 Oph, V2612 Oph, V1363 Ori, V351 Peg, V357 Peg, Y Sex, V1123 Tau, and W UMa, which was conducted in the frame of the W UMa Project. Together with 51 already covered by the project and an additional 67 in the existing literature, these systems bring the total number of contact binaries with known combined spectroscopic and photometric solutions to 138. It was found that mass, radius, and luminosity of the components follow certain relations along the MS and new empirical power relations are extracted. We found that 30 per cent of the systems in the current sample show extreme values in their parameters, expressed in their mass ratio or fill-out factor. This study shows that, among the contact binary systems studied, some have an extremely low mass ratio (q < 0.1) or an ultrashort orbital period (Porb < 0.25 d), which are expected to show evidence of mass transfer progress. The evolutionary status of these components is discussed with the aid of correlation diagrams and their physical and orbital parameters compared to those in the entire sample of known contact binaries. The existence of very short orbital periods confirms the very slow nature of the merging process, which seems to explain why their components still exist as MS stars in contact configurations even after several Gyr of evolution.

New low mass ratio contact binaries in the Catalina Sky Survey

“…Although these systems have different fill-out factors (99%, 24%, 51 − 70% and 53% respectively) and primary masses, all of them show indications of the presence of a third body. ASAS J102556+2049.3 has a large period decrease over 11 years (𝑑𝑃/𝑑𝑡 = −3.4 × 10 −6 d yr −1 ) (Kjurkchieva et al 2019b), ASAS J083241+2332.4 shows a sinusoidal period variation (Sriram et al 2016), the spectroscopically studied KR Com has a third light contribution at the level of 60% (Gazeas et al 2021a) and V1222 Tau has one of the largest period variations 𝑑𝑃/𝑑𝑡 = +8.19 × 10 −6 d yr −1 and an extreme O'Connell effect. Like in many LMRs, the long term period variations are associated with the presence of an additional component (Pribulla & Rucinski 2006) that plays a particular role in angular momentum evolution (Eggleton & Kisseleva-Eggleton 2006).…”

CoBiToM Project -- II: Evolution of contact binary systems close to the orbital period cut-off

“…Moreover, six of these systems also have an orbital period shorter than 0.22 d. Although these systems were considered to have unstable orbits and are heading towards merg-ing, we found that they are very stable, and in an quite early contact phase. Gazeas et al (2021a) showed an interesting trend in the fill-out factor parameter, as compared with the orbital period and mass ratio. It appears that systems with shorter orbital periods tend to have shallow contact configurations.…”

“…We used the Wilson-Devinney (W-D) code (Wilson 1979(Wilson , 1990 appended with the Monte Carlo (MC) algorithm as the search procedure, as described in detail in Zola et al ( 2004); Gazeas et al (2021a). We took advantage of the fact that the applied method does not require initial values for the free parameters.…”

“…In Fig. 9 these theoretical boundaries are depicted for the uniform sample of contact binary systems from Gazeas et al (2021a) and our sample. A similar investigation was made by Li & Zhang (2006), but without accounting for ultra-short contact binaries.…”

“…The solid lines indicate the inner and outer theoretical limits for the systems filling the inner and outer Roche lobe, respectively. The filled black points represent the sample of 138 W UMa-type binaries fromGazeas et al (2021a), while the red star markers represent the ultra-short period binary systems of the present study. The uncertainty on the red star markers is smaller than the marker size.…”