V424 Cep Halpna and HeI6678 spectra

The two eclipses observed in the light curves yield a refined orbital period P=4.93d, an eccentricity e=0.02, and an apsidal period U=730yr. The eclipse O-C curve is not linear. Combined with the apsidal period, this indicates the presence of a third component in the system.

This conclusion was confirmed by a comparison of predicted and observed absolute fluxes. The masses of the binary pair are 8.7M_{sun}_ and 6.3M_{sun}_, their radii are 6.0R_{sun}_ and 3.5R_{sun}_, and the luminosities are log(L/L_{sun}_) 3.80 and 3.11. The TESS light curve shows oscillations with a dominant period of 0.17d.

They are coherent throughout the orbital cycles with a stable amplitude, except during the (partial) eclipse of the primary star. This indicates that this is the pulsator. Its temperature is 21000K.

The third-light component contributes no more than 15% to the total light of the system in the TESS wavelength band and 20% in the K band. V424 Cep is not a Maia variable, but rather a beta Cep star. This result highlights the importance of combining photometric light-curve solutions with absolute flux models and spectroscopic observations.