Improved model of the triple system V746 Cassiopeiae that has a bipolar magnetic field associated with the tertiary.

V746 Cas is known to be a triple system composed of a close binary with an alternatively reported period of either 25.^d4 or 27.^d8 and a distant third component in a 170 yr (62 000 d) orbit. The object was also reported to exhibit multiperiodic light variations with periods from 0.^d83 to 2.^d50, on the basis of which it was classified as a slowly pulsating B star. Interest in further investigation of this system was raised by the recent detection of a variable magnetic field. Analysing spectra from four instruments, earlier published radial velocities, and several sets of photometric observations, we arrived at the following conclusions: (1) The optical spectrum is dominated by the lines of the B-type primary (T_{eff 1} 16 500(100) K), contributing 70% of the light in the optical region, and a slightly cooler B tertiary (T_{eff 3} 13 620(150) K). The lines of the low-mass secondary are below our detection threshold; we estimate that it could be a normal A or F star. (2) We resolved the ambiguity in the value of the inner binary period and arrived at a linear ephemeris of T_{super. conj.}=HJD 2 443 838.78(81)+25.^d41569(42)× E. (3) The intensity of the magnetic field undergoes a sinusoidal variation in phase with one of the known photometric periods, namely 2.^d503867(19), which we identify with the rotational period of the tertiary. (4) The second dominant photometric 1.^d0649524(40) period is tentatively identified with the rotational period of the broad-lined B-type primary, but this interpretation is much less certain and needs further verification. (5) If our interpretation of photometric periods is confirmed, the classification of the object as a slowly pulsating B star should be revised. (6) Applying an N-body model to different types of available observational data, we can constrain the orbital inclination of the inner orbit to 60°<i1< 85° even in the absence of binary eclipses, and we estimate the probable properties of the triple system and its components. [ABSTRACT FROM AUTHOR]