A precontact binary and a shallow contact binary are in the same field

The period changes of two close binaries, V1107 Cas and AX Cas, which are in the same field, were investigated. Their periods both show a long-term decrease. After further analysis, we found that the periods have their respective cyclic oscillations (T3 = 6.74 ± 0.24 yr for V1107 Cas and T3 = 13.8 ± 0.3 yr for AX Cas), which are possibly caused by a third body due to the light-time effect. We also obtained the complete VRcIc light curves for V1107 Cas and analyzed them with the 2010 version of the Wilson–Devinney code. The photometric results reveal that V1107 Cas is a W-type shallow contact (15.2%±1.8%) binary, with a mass-ratio of 1.797 ± 0.006. The period variation and photometric solution suggest that V1107 Cas is a newly formed contact binary system. Moreover, we estimated the fundamental parameters for V1107 Cas. They are: M1 = 0.39 ± 0.01 M , M2 = 0.70 ± 0.03 M , R1 = 0.52 ± 0.10 R , R2 = 0.68 ± 0.12 R , L1 = 0.178 ± 0.108 L , and L2 = 0.196 ± 0.116 L . Then, based on the coplane assumption, we deduced the masses of possible third bodies to be M3 = 0.091 ± 0.019 M for V1107 Cas and M3 = 0.325 ± 0.029 M for AX Cas. Finally, we inferred the evolutional stage of AX Cas, and believe that it is a precontact binary. Thus, the precontact binary AX Cas and the shallow contact binary V1107 Cas have adjoining evolutional stages.