First photometric study of the W UMa system GSC 1042-2191

•The first analysis of the light curve of the W UMa system GSC 1042–2191 were made.•The orbital and physical parameters of the system were obtained.•The system was found a low mass ratio, A-type over-contact binary with a fill out parameter of f 65.01%.

We present new photometric observations covering eight minima times for the eclipsing binary GSC 1042-2191. The light curves in BVRIBVRI colors were analyzed by using WD-code for the system parameters. Eight minima times were obtained from the new observations. The system is found a low mass ratio (q = 0.148), A-type over-contact binary with a fill out parameter of f = 65.01 ± 12.18%. The preliminary absolute dimensions (M1= 1.26 ± 0.06 M⊙, M2 = 0.18 ± 0.06 M⊙, R1 = 1.54 ± 0.20 R⊙, R2 = 0.69 ± 0.01 R⊙, L1L1 =3.30 ± 0.30 L⊙ and L2L2 = 0.59 ± 0.20 L⊙) indicate the very much oversized and over-luminous secondary component, by assuming the present luminosity of the secondary is its main sequence luminosity, we predict the original mass is about 0.8 M⊙, this means the present secondary could be transferred and/or lost 77% of its original mass and only its core is left.