Detailed TESS-Based Light Curve Modeling and Fundamental Parameter Estimation of 27 W UMa-Type Contact Binaries

TL;DR

This paper addresses the need for detailed absolute parameter determinations of W UMa-type contact binaries by exploiting the all-sky, high-cadence photometry from TESS for 27 previously uncharacterized systems. The authors apply BSN light curve modeling, enhanced with MCMC refinement, and derive absolute parameters using an updated period–semi-major axis relation, complemented by cross-validation with ASAS-SN data and additional TESS sectors. They classify each system as A- or W-subtype, identify starspot activity in seven targets, and analyze the parameter space of 484 similar binaries to quantify subtype discriminants, revealing that primary-star properties and orbital period are the main separators. The results provide robust absolute parameters, support evolutionary interpretations, and demonstrate the utility of TESS-era photometric modeling for contact binaries, with implications for mass-transfer histories and stability assessments. The study also confirms consistency with empirical L–R and T_h–M_m relations and places several systems near critical evolutionary boundaries, highlighting the ongoing need for precise, multi-band, space-based photometry in large-scale binary star studies.

Abstract

We performed a comprehensive analysis of 27 short period contact binary systems for which no light curve analysis had previously been reported. Photometric time-series data from the TESS mission were used in this analysis. The observational results were validated using additional TESS sectors, along with complementary photometric observations from the ASAS-SN survey. The photometric light curves of the 27 contact binary systems were analyzed with the BSN application. Model solutions were obtained through iterative fitting followed by MCMC-based refinement to derive reliable system parameters, and starspot configurations were incorporated for seven targets exhibiting O'Connell effect asymmetries. The absolute parameters of the target systems were derived using the empirical parameter relationship between orbital period and semi-major axis. Based on the results of the light curve solutions and the estimated absolute parameters, five of the analyzed systems are identified as A-subtype, while the remaining targets belong to the W-subtype. We analyzed a sample of 484 W UMa contact binaries to identify the physical and orbital parameters that most effectively distinguish A-subtype from W-subtype systems using t-statistics. Three targets exhibited extremely low mass ratios, and their orbital analysis confirmed that they are dynamically stable. The evolutionary states of the systems were examined, showing that lower-mass companions are generally more evolved, while more massive components remain less evolved. The positions of the systems and their stellar components were compared across four diagrams derived from empirical parameter relationship studies, showing good agreement with the linear fits.

Figures (8)

• Figure 1: The photometric light curve of TIC 184565222, together with its first through third derivatives (displayed from the top to the bottom panels), is presented as a sample of estimating the initial mass ratio for the targets. TIC 184565222 exhibits a mass ratio of $q = 0.7714(102)$ using the Kouzuma method. It should be noted that in this method, the more massive component is introduced as $M_1$ and the less massive component as $M_2$. The vertical-axis units for these panels are W m$^{-2}$, 10 W m$^{-2}$ day$^{-1}$, $10^{2}$ W m$^{-2}$ day$^{-2}$, and $10^{4}$ W m$^{-2}$ day$^{-3}$, respectively.
• Figure 2: Corner plot for the TIC 293775345 binary system, shown as a representative example among the target systems. The plot illustrates the posterior probability distributions and correlations among the five main parameters obtained from the MCMC analysis.
• Figure 3: Photometric light curve solutions for the target binary systems.
• Figure 4: Observed and synthetic light curves for the 27 contact binary systems. The residuals are shown in the bottom panel.
• Figure 5: Three-dimensional view of the TIC 468265910 binary system at four orbital phases (0, 0.25, 0.50, and 0.75, respectively). This system is shown as a representative example among the targets, illustrating the relative positions of the component stars throughout the orbit.