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    BSN. IV. The First Multiband Light Curve Study of Five W UMa-type Contact Binary Systems
    (Iop Publishing Ltd, 2025) Poro, Atila; Michel, Raul; Coliac, Jean-Francois; Nastaran, Maryam; Fernandez Lajus, Eduardo; Javier Tamayo, Francisco; Aceves, Hector
    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-semimajor 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.
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    BSN. V. The First Detailed Light Curve Modeling of Eight Totally Eclipsing Contact Binary Stars Using Ground-based and TESS Observations
    (Iop Publishing Ltd, 2025) Poro, Atila; Michel, Raul; Javier Tamayo, Francisco; Hedayatjoo, Mahya; Aceves, Hector; Alicavus, Fahri
    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 BV RcIc 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 Transiting Exoplanet Survey Satellite 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 day, separating the systems into two distinct groups for orbital periods shorter than 0.6 day. 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.
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    THE FIRST MULTICOLOUR PHOTOMETRY OF THE V840 LYR CONTACT BINARY STAR
    (Univ Nacional Autonoma Mexico, Inst De Astronomia, 2024) Tanrıver, Mehmet; Michel, Ral; Bulut, Ahmet; Aceves, Hector; Keskin, Ahmet
    Light curves for the total-eclipsing binary system V840 Lyr in the V, R degrees, and I degrees bands are presented; these display the O'Connell effect. Analysis was performed with the Phoebe031a software revealing that V840 Lyr is a W-type contact binary with a degree of contact factor of f = 15.1 +/- 5.6%, a mass ratio of q = 0.4509 +/- 0.0705, an inclination of i = 86.7 degrees, and a temperature difference of triangle T = 45 K. An asymmetry in the light curves was modeled assuming a cool spot located on the secondary star. The period changes of the system are examined by combining our recently found times of light minima together with those in the literature. Absolute parameters were obtained as M1 = 0.74M((R)), M2 = 0.34M((R)), R1 = 0.74R((R)), and R2 = 0.51R((R)) from our photometric solutions, using some empirical relations. The long-term period increase and the contact configuration indicate that V840 Lyr will evolve into a fill-out overcontact binary.