Continuous O ’Connell effect and period variations of solar-like totally eclipsing contact binary BO Ari

We obtained newly BV$R_c{I}_c$ light curves for the contact binary BO Ari in 2023. The multi-color light curves were analyzed using the Wilson–Devinney (2013) program, which solutions reveal that BO Ari is a middle contact binary with q = 0.1778, f = 48% and a small temperature difference of 92 K. All minimum times were collected to re-calculated O-C. The O-C curves show a cyclic oscillation ($A_3$ = 0.00337 d, $T_3$ = 16.35 yr) superimposed on a long-term decreasing (dP/dt = $-1.63\times 10^{-7}$ d ${\mathrm{yr}}^{-1}$). This secular period decrease may be due to mass transfer from the more massive component to the less massive one. The cyclic trend was explained by the light-travel time effect due to the presence of a third body or magnetic activity. With this long-term mass transferring, the fill-out degree will increase. Furtherly, BO Ari will evolve into a deeply contact binary. In addition, during the monitoring of the space telescope Transiting Exoplanet Survey Satellite (TESS), it is the first time to discover continuous variation of the O’Connell effect in each cycle, obviously the positive O’Connell effect changes to a negative one over a short time. These phenomena imply the presence of possible magnetic activity on the surface of the component. Based on these fitting parameters, the hot spot and dark spot were found on the components.