BSN-III: The First Multiband Photometric Study on the Eight Total Eclipse Contact Binary Stars

TL;DR

This paper presents a comprehensive multiband photometric analysis of eight total-eclipse contact binary stars, revealing period variations, potential tertiary companions, starspots, and evolutionary status, thereby advancing understanding of W UMa-type systems.

Contribution

It provides the first multiband photometric study of these eight contact binaries, including period analysis, light curve modeling, and evolutionary insights, with evidence of tertiary companions and starspots.

Findings

Four systems show secular period decrease.

Two systems exhibit secular period increase.

One system shows cyclic variation likely due to a tertiary companion.

Abstract

This study continues our in-depth investigation of total-eclipse W Ursae Majoris-type contact binaries by analyzing eight new systems, complementing our previous work. Multiband $BVR_cI_c$ photometric data were acquired through ground-based observations at an observatory in Mexico, from which new times of minima were determined. Our analysis of orbital period variations using the O-C method revealed that one system shows no long-term variation, four systems exhibit a secular decrease in their orbital periods, and two systems exhibit a secular increase, suggesting mass transfer between the components. Notably, one system displays a cyclic variation with an amplitude of 0.00865 days and a period of 10.49 years, which we attribute to the light travel time effect induced by a tertiary companion, possibly a brown dwarf. We modeled the light curves using the PHOEBE Python code. Six of the target systems required the inclusion of a cold starspot on one of the system's stars due to the asymmetry observed in the maxima of their light curves. Absolute parameters were estimated using the Gaia DR3 parallax method. Using the components' effective temperatures and masses, we classified five of the systems as W-subtype and three as A-subtype. The stellar evolution was illustrated through the mass-radius and mass-luminosity diagrams. Furthermore, we investigated the dynamical stability of two systems with extremely low mass ratios.