Orbital period variation of W UMa binary star V2802 Orionis

Abstract

This study investigates the orbital period variation and physical parameters of the eclipsing binary system V2802 Orionis. Observations were conducted at the Regional Observatory for the Public, Nakhon Ratchasima (ROP-NMA), under the National Astronomical Research Institute of Thailand (NARIT), using Johnson-Cousins B, V, R_C, and I_C filters. Light curves obtained between 2021 and 2023 were analyzed with the Wilson–Devinney (W-D) code, revealing a mass ratio of q = 2.902(±0.006), an inclination of i = 88.6(±0.4) degree, and a secondary star temperature T₂ = 5030(±3) K. Our results indicate that V2802 Orionis is a W-type W UMa binary star with a shallow degree of contact (16.6 %) and variability due to a spot on the primary component. The orbital period shows a secular decrease at a rate of 1.12(±0.09)×10⁻⁷ day year⁻¹, attributed to mass transfer from the more massive to the less massive component. Additionally, a period variation with a cycle 5.1(±0.1) years suggests the presence of a third body, with a mass of 0.14(±0.01) M_☉ and a separation of 3.2(±0.1) AU from the binary system. The masses, radii, and luminosities of the primary and secondary stars are estimated as M₁ = 0.65(±0.001) M_☉, M₂ = 0.77 M_☉, R₁ = 0.56(±0.01) R_☉, R₂ = 0.91(±0.01) R_☉, L₁ = 0.21(±0.01) L_☉, and L₂ = 0.48(±0.01) L_☉. Evolutionary analysis on the Hertzsprung-Russell diagram shows that the primary star (less massive) has evolved away from the main-sequence, while the secondary (more massive) remains on the main sequence star.