BSN-IV: The First Multiband Light Curve Study of Five W UMa-type Contact Binary Systems

TL;DR

The paper presents a multiband photometric study of five W UMa-type contact binaries, deriving orbital and absolute parameters through light-curve modeling with BSN and empirical period–semi-major axis ($P$–$a$) relations, complemented by O–C analyses of period variations. It finds two systems with linear and two with parabolic orbital-period trends, indicating mass transfer with quantified rates, and classifies three targets as A-subtype and two as W-subtype, while assessing their thermal equilibrium and evolutionary status. Absolute parameters are obtained using the $P$–$a$ calibration due to limitations in Gaia parallaxes, revealing near-threshold low-mass-ratio systems BF Dor and J004331, and placing the binaries within empirical $M$–$R$, $M$–$L$, and $T_h$–$M_m$ frameworks for evolutionary interpretation. The work highlights the value of combined ground- and space-based photometry, MCMC-based uncertainty quantification, and empirical parameter relations for characterizing short-period contact binaries and probing their stability and merger pathways.

Abstract

In this work, we present a detailed investigation of five contact binary systems of the W Ursae Majoris (W UMa) type. Multiband photometric observations were conducted using ground-based telescopes in both the northern and southern hemispheres, yielding new times of minima. O-C diagram analysis reveals that two systems exhibit parabolic trends, indicating a gradual long-term decrease in their orbital periods. The light curves were modeled using version 1.0 of the BSN application, with one system requiring the inclusion of a cool starspot to achieve a satisfactory fit. We examined empirical relationships between orbital period and fundamental parameters, identifying the period-semi-major axis (P-a) relation as the most robust correlation, which was used to estimate absolute parameters. To statistically assess thermal equilibrium, we analyzed temperature differences between components and found that 90% of systems exhibit less than 9.4% contrast. Two target systems with extremely low mass ratios were identified, and their orbital stability was evaluated. Based on the effective temperatures and component masses, two systems were classified as W-subtype and three as A-subtype. The evolutionary status of the binaries was assessed through their locations in mass-radius, mass-luminosity, and other empirical diagrams, and initial component masses as well as total mass loss were also estimated.

Figures (8)

• Figure 1: The O-C diagrams of the target systems, with residuals at the bottom
• Figure 2: The sum of squared residuals as a function of mass ratio.
• Figure 3: The corner plots of the target systems were determined by MCMC modeling.
• Figure 4: 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 5: Three-dimensional views of the stars in the target binary systems at orbital phases 0.0, 0.25, 0.5, and 0.75, respectively.