Marginally low mass ratio close binary system V1191 Cyg

Abstract In this study, we present photometric and spectroscopic variations of the extremely small mass ratio ( q  ≃ 0.1) late-type contact binary system V1191 Cyg. The parameters for the hot and cooler companions have been determined as M h  = 0.13 (1) M ⊙ , M c  = 1.29 (8) M ⊙ , R h  = 0.52 (15) R ⊙ , R c  = 1.31 (18) R ⊙ , L h  = 0.46 (25) L ⊙ , L c  = 2.71 (80) L ⊙ , the separation of the components is a  = 2.20 (8) R ⊙ and the distance of the system is estimated as 278 (31) pc. Analyses of the times of minima indicates a period increase of dP dt = 1.3 ( 1 ) × 10 - 6 days / yr that reveals a very high mass transfer rate of dM dt = 2.0 ( 4 ) × 10 - 7 M ⊙ / yr from the less massive component to the more massive one. New observations show that the depths of the minima of the light curve have been interchanged.