BSN-V: The First Detailed Light Curve Modeling of Eight Totally Eclipsing Contact Binary Stars Using Ground-Based and TESS Observations

TL;DR

This study presents the first detailed light-curve modeling of eight totally eclipsing W UMa-type contact binaries using simultaneous ground-based multiband photometry and TESS time-series. It derives updated ephemerides, classifies orbital-period variations, and yields absolute stellar parameters by combining Gaia DR3 parallaxes with photometric modeling, revealing a break in the orbital-period–hotter-component-temperature relation around $P=0.27$ days and confirming A- and W-type classifications. The results advance understanding of contact-binary structure and evolution, including mass-transfer rates for systems with parabolic period changes, and place components on $M$–$R$ and $M$–$L$ diagrams relative to ZAMS and TAMS. The work demonstrates the efficacy of integrating PHOEBE with BSN MCMC for robust light-curve solutions and Gaia-based parameter estimation in populations of short-period binaries.

Abstract

This study broadens our comprehensive investigation of total-eclipse W Ursae Majoris-type contact binaries by analyzing eight additional systems, continuing our previous research. Multiband $BVR_cI_c$ photometric data were obtained at an observatory in Mexico, from which new times of minima were determined. All target systems also had available space-based TESS time-series data. Orbital period variations were studied for eight target systems, showing either linear or parabolic trends. The target systems exhibiting parabolic trends demonstrated a sustained decrease in their orbital periods over time. We modeled the light curves utilizing the PHOEBE Python code in combination with the BSN application. We revisited the relationship between orbital period and the temperature of the hotter component in contact binary systems using an empirical approach. Our analysis identified a clear break at P=0.27 days, separating the systems into two distinct groups for orbital periods shorter than 0.6 days. Following the determination of stellar extinction, absolute parameters for seven systems were estimated employing parallax measurements from Gaia DR3. Based on the components' effective temperatures and masses, the systems were classified into A- and W-subtypes. Their evolutionary states were illustrated using mass-radius and mass-luminosity diagrams.

Figures (6)

• Figure 1: O-C diagrams for the eight target systems, with corresponding residuals shown in the bottom panel.
• Figure 2: The sum of squared residuals as a function of mass ratio.
• Figure 3: The colored dots represent the observed light curves of the systems in different filters, and the synthetic light curves, generated using the light curve solutions, are also shown. Residuals are shown at the bottom of each panel.
• Figure 4: Three-dimensional representations of the target binary stars shown at orbital phases 0, 0.25, 0.5, and 0.75, respectively.
• Figure 5: The updated empirical relationship between orbital period and hotter component temperature in contact binary systems.