2025RAA....25e5006T

In this paper, new light curve fitting and orbital period change analysis of two contact binaries NSVS 9023048 and NSVS 2461789 are presented. We found that both of them are totally eclipsing contact binaries. Our photometric solutions suggest that NSVS 9023048 is a deep contact binary (q = 10.14, f = 69.2%), however, NSVS 2461789 is a shallow one (f = 24.4%, q = 3.08). The asymmetric light curves of NSVS 2461789 and NSVS 9023048 can be explained by the star-spot activity. At the same time, using the available eclipse times, we first studied the orbital period changes of these two targets. It is discovered that the period of NSVS 9023048 is decreasing at a rate of dP / dt = -1.17 × 10^–6 day yr^–1, which can be explained by mass transfer from the more massive star to the less massive one or angular momentum loss. In addition, the O - C diagrams of NSVS 9023048 and NSVS 2461789 show possible cyclic oscillations with a period of 7.29 yr and 9.91 yr, respectively. The cyclic oscillations may be caused by the light-travel time effect due to the presence of a third component. The mass of the tertiary companion is determined to be M₃sin(i₃) = 9.05 M_⊙ _for NSVS 9023048 and M₃sin(i₃) = 0.11 M_⊙ for NSVS 2461789. Based on our calculations, the third body of NSVS 9023048 may be a black hole candidate. Our study also reveals that NSVS 9023048 is stable now.