V745 Cassiopean interacting young massive binary in a multiple-star system

We present spectroscopic observations of the massive early-type system V745 Cas, embedded in a multiple-star system. The brightest star of the system is the eclipsing binary V745 Cas with an orbital period of 1.41 d. The radial velocities of both components and light curves obtained by INTEGRAL and Hipparcos missions were analysed. The components of V745 Cas are shown to be a B0 V primary with a mass M_p = 18.31±0.51 M_⊙ and radius R_p = 6.94±0.07 R_⊙ and a B(1-2) V secondary with a mass M_s = 10.47±0.28 M_⊙ and radius R_s = 5.35 ± 0.05 R_⊙. Our analysis shows that both components fill their corresponding Roche lobes, indicating double contact configuration. Using the UBVJHK magnitudes and interstellar absorption, we estimated the mean distance to the system as 1700 ± 50 pc. The locations of the component stars in the mass-luminosity, mass-radius, effective temperature-mass and surface gravity-mass are in agreement with those of the main-sequence massive stars. We also obtained UBV photometry of the three visual companions and we estimate that all are B-type stars based upon their de-reddened colours. We suspect that this multiple system is probably a member of the Cas OB4 association in the Perseus arm of the Galaxy.