A high-mass-ratio red-dwarf contact binary with an extremely cool close-in red dwarf

1SWASP J161335.80-284722.2 (hereafter J161335) is an eclipsing red -dwarf binary with an orbital period of 0.229778 d, which is around the short-period limit for contact binaries. Three sets of multi -color light curves of J161335 were obtained from different telescopes in 2015 and 2016 and are analyzed using the Wilson-Devinney method. We discovered that the system is a W-type contact system with a contact degree of 19% and a high mass ratio of 0.91. By using all available eclipse times, we found that the observed - calculated (0 - C) diagram displays a cyclic oscillation with an amplitude of 0.00196(+/- 0.00006) d and a period of 4.79(+/- 0.14) yr while it undergoes a downward parabolic change. This downward variation corresponds to a continuous decrease in the orbital period at a rate of dP/dt= -4.26( 0.01) x 10(-7) d yr(-1). The small -amplitude oscillation is explained as the light travel -time effect from the gravitational influence of a third body with a lowest mass of M-3 = 0.15(+/- 0.01)M-circle dot. In solving the light curves, we found that the third light is increasing, with the wavelength suggesting that the third body may be a cool red dwarf. This is in agreement with the results obtained by analyzing the O - C diagram. The tertiary red dwarf is orbiting the central red -dwarf binary at an orbital separation of 2.8(+/- 0.2) au. These results suggest that the J161335 system may be formed through early dynamical interaction where the original low-mass component was replaced by a higher-mass third body and the lower-mass component was kicked out to a wider orbit.