Circular orbit solution for V742 Cas (Table 1). Left: RV curve of the narrow-lined component (dashed line) with the RVs measured in the He I λ6678 line (black circles). The bottom panel shows the residuals in units of σ. Right: Relative astrometric orbit derived from interferometry. The orbital motion is clockwise. The black plus symbol corresponds to the location of the primary Be star, while the best-fit companion orbit is plotted as a black dashed line. Error ellipses correspond to the interferometric measurements with 5σ uncertainties (MIRC-X in blue and MYSTIC in red). The associated calculated positions are plotted as black crosses. Finally, the line of nodes is plotted as a gray solid line, the green cross shows the ascending node, and the smaller yellow cross shows the superior conjunction of the Be star that is used as T₀ for the phased plots. The two MYSTIC points with larger error ellipses correspond to angular separations below the nominal resolution of CHARA in the K-band.