First period investigation of detached binary star AM Tau

• We obtained several new CCD times of light minimum.
• We first ever analyzed the periodic variations of AM Tau.
• The secular period decrease may result from enhanced stellar wind.
• Two cyclic oscillations may reveal AM Tau a quadruple system.

AM Tau is a detached eclipsing binary with the secondary component more evolved than the primary one. The period changes of this neglected eclipsing binary are analyzed based on four times of primary minimum obtained between 2007 and 2016 together with those collected from the literature. It is detected that the general trend of the O-C curve shows a downward parabolic variation, which reveals a continuous period decrease at a rate of dP/dt=−9.0×10−7(±0.2)dP/dt=−9.0×10−7(±0.2) d yr−1,−1, meanwhile, the system undergoes two cyclic oscillations with periods of 24.1 and 8.8 years. The continuous decrease in the orbital period may be caused by angular momentum loss (AML) via an enhanced stellar wind of the evolved secondary star. The two cyclic variations in the O-C diagram are interpreted by the light travel-time effect via the presence of two additional stellar companions with masses estimated as M3sin i3 ∼ 1.36 M⊙ and M4sin i4 ∼ 0.33 M⊙. Their orbital separations are about 14 and 8 AU, respectively, and the orbital periods are almost in 3 : 1 resonance orbits.