V723 Persei: A short-period Algol-like near-contact binary

Complete multi-color photometric observations in the BVRC/(C) bands and low-resolution spectra of the short-period binary V723 Per are presented for the first time. The stellar atmospheric parameters of effective temperature, gravitational acceleration, and metallicity are determined as T-eff = 7407 +/- 53 K, log g = 3.98 +/- 0.10 cms(-2), and [Fe/H] = -0.25 +/- 0.10 dex, respectively. Photometric solutions are obtained by analyzing the phased light curves with the Wilson-Devinney method. We found that V723 Per is an Algol-like semi-detached-type near-contact binary with a mass ratio of q = 0.3168 +/- 0.0011. The secondary component is filling the critical Roche lobe, while the primary is nearly filling its Roche lobe (the filling degree is about 80.93%). The primary component contributes about 96% of the luminosity of the total system, and the temperature difference between the two component stars is about 3000 K. All available times of light minimum, including three new observed eclipse times, were used to construct the O - C curve. The period shows a continuous increase at a rate of dP/dt = +7.63(+/- 0.75) x 10(-6) dyr(-1) superposed with a periodic oscillation of amplitude of 0.0392 d and period 17.4 yr. The period increase could be explained by mass transfer from the secondary component to the primary one on the thermal timescale, which is in agreement with the semi-detached configuration. The cyclic change may be caused by the light-time effect due to a massive (M-3 = 3.03 M-circle dot) but quite faint (L-3/L-total similar or equal to 3%) tertiary companion orbiting the central binary. Such a third body might be a black hole or a binary with two nearly identical stars. More observations are required in the future to confirm our conclusion about the cycle variation and tertiary companion.