First Detailed Photometric Investigation on the Nature of Contact Binary System AA Cet

The TESS light curve(LC)of the marginal contact binary A A Cet was analyzed simultaneously with the radial velocity and the orbital period(OP)change of the system was investigated.The physical parameters of the system were obtained by analyzing the LC of A A Cet with the Wilson-Devinney method,and the absolute parameters of the components were calculated using the results obtained.For the components of AA Cet,the masses and radii were calculated as M_(1)=1.39±0.04 M_⊙,M_(2)=0.48±0.02 M_⊙,and R_(1)=1.64±0.03 R_⊙,R_(2)=1.01±0.04 R_⊙,respectively.AA Cet is a marginal contact binary with a temperature difference of 1305 K between its components.A total of 14 eclipse times were obtained from the TESS data and used in the OP analysis together with those collected from the literature.It has been observed that the change in the OP of AA Cet is in the form of a decreasing parabola.Conservative mass transfer between the components has been interpreted as the reason for this change.The OP decrease amount of A A Cet was obtained as dP/dt=0.0062±0.0006 s yr^(-1).and the reason for this decrease was attributed to a 3.3(9)×10^(-8)M_⊙.mass transfer per year from the more massive component to the less massive one.The age of A A Cet has been estimated as 7 Gyr,as the age of contact systems helps us to understand their evolution.