2026ApJ...997..289W

We present 22 sets of light curves and one radial velocity curve for the W UMa-type total eclipse contact binary system V2790 Ori, derived by combining all available public photometric data, the photometric data in previous studies, and our own spectroscopic and decade-long photometric observations. Our simultaneous analysis of the light curves and radial velocity curve shows that V2790 Ori is a W-subtype contact binary with a mass ratio of q = 0.322(±0.001) and a shallow contact degree of 14.8(±0.6)%. The orbital period analysis based on 445 eclipsing minima reveals a secular decrease at a rate of $\dot{P}=-3.18(\pm 0.75)\times 1{0}^{-8}\,\mathrm{days}\,{\mathrm{yr}}^{-1}$, superimposed with a cyclic variation with an amplitude of A = 8.98(±2.19) × 10^–4 days and a period of P₃ = 7.44(±0.52) yr. The secular decrease is caused by angular momentum loss via magnetic braking, while the cyclic period variation is explained by the light-travel time effect due to a third body, which is likely to be a brown dwarf. Furthermore, our analysis indicates a mass transfer from the more massive component to the less massive one at a rate of 1.22(±0.29) × 10^–8M_⊙ yr^–1. A model with a cool spot on each component was adopted to fit the O'Connell effect observed in the light curves. Since the O'Connell effect varies over time, we identified a solar-like magnetic activity cycle with a period of approximately 5.4 yr by analyzing the magnitude difference (Δm) at the two light maxima and the O'Connell effect ratio. In addition, evolutionary analysis suggests that V2790 Ori is a newly formed contact binary that evolved from a detached phase into the present contact configuration.