V746 Cas is known to be a triple system composed of a close binary with an alternatively reported period of either 25 \aas@@fstack { d } 4 or 27 \aas@@fstack { d } 8 and a distant third component in a 170 yr ( 62000 d ) orbit .
The object was also reported to exhibit multiperiodic light variations with periods from 0 \aas@@fstack { d } 83 to 2 \aas@@fstack { d } 50 , 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 } \sim 16500 ( 100 ) { K } ) , contributing 70 % of the light in the optical region , and a slightly cooler B tertiary ( T _ { eff 3 } \sim 13620 ( 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 } ~ { } 2443838.78 ( 81 ) +25 \aas@@fstack { d } 41569 ( 42 ) \times E .
( 3 ) The intensity of the magnetic field undergoes a sinusoidal variation in phase with one of the known photometric periods , namely 2 \aas@@fstack { d } 503867 ( 19 ) , which we identify with the rotational period of the tertiary .
( 4 ) The second dominant photometric 1 \aas@@fstack { d } 0649524 ( 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 \sim 60 ^ { \circ } < i _ { 1 } < 85 ^ { \circ } even in the absence of binary eclipses , and we estimate the probable properties of the triple system and its components .