We present the orbital period study and the photometric analys of the contact binary system V728 Her .
Our orbital period analysis shows that the period of the system increases ( dP / dt = 1.92 \times 10 ^ { -7 } dyr ^ { -1 } ) and the mass transfer rate from the less massive component to more massive one is 2.51 \times 10 ^ { -8 } M _ { \odot } y ^ { -1 } .
In addition , an advanced sinusoidal variation in period can be attributed to the light–time effect by a tertiary component or the Applegate mechanism triggered by the secondary component .
The simultaneous multicolor BVR light and radial velocity curves solution indicates that the physical parameters of the system are M _ { 1 } = 1.8 M _ { \odot } , M _ { 2 } = 0.28 M _ { \odot } , R _ { 1 } = 1.87 R _ { \odot } , R _ { 2 } = 0.82 R _ { \odot } , L _ { 1 } = 5.9 L _ { \odot } , and L _ { 2 } = 1.2 L _ { \odot } .
We discuss the evolutionary status and conclude that V728 Her is a deep ( f =81 % ) , low mass ratio ( q =0.16 ) contact binary system .