Absolute parameters of three southern eclipsing binaries: DQ Car, BK Ind, and V4396 Sgr

We present combined photometric and spectroscopic analyses of the three southern eclipsing binary stars: DQ Car, BK Ind, and V4396 Sgr. Radial velocity curves of these three systems were obtained at the South African Astronomical Observatory, and their light curves from the available data bases and surveys were used for the analysis. 75 new times of minima for these three eclipsing binaries were derived, and their ephemerides were updated. Only the O-C diagram of DQ Car indicates a cyclical variation, which was interpreted in terms of the light-time effect due to a third body in the system. Our final models describe these three systems as Algol-like binary stars with detached configurations. The masses and radii were found to be M₁ = 1.86(±0.17) M_⊙, R₁ = 1.63(±0.06) R_⊙ and M₂ = 1.74(±0.17) M_⊙, R₂ = 1.52(±0.07) R_⊙ for the primary and secondary components of DQ Car; M₁ = 1.16(±0.05) M_⊙, R₁ = 1.33(±0.03) R_⊙ and M₂ = 0.98(±0.04) M_⊙, R₂ = 1.00(±0.03) R_⊙ for BK Ind; and M₁ = 3.14(±0.22) M_⊙, R₁ = 3.00(±0.09) R_⊙ and M₂ = 3.13(±0.24) M_⊙, R₂ = 2.40(±0.08) R_⊙ for V4396 Sgr, respectively. The distances to DQ Car, BK Ind, and V4396 Sgr were derived to be 701(±50), 285(±20), and 414(±30) pc from the distance modulus formula, taking into account interstellar extinction. The evolutionary status of these three systems was also studied. It has been found that the components of DQ Car are very young stars at the age of ∼25 Myr and those of BK Ind and V4396 Sgr are evolved main-sequence stars at the ages of ∼2.69 Gyr and ∼204 Myr, respectively.