A Maia-type candidate was misclassified: V424 Cep is an eclipsing β Cep-type pulsator in a triple system

Context. V424 Cephei is an eclipsing binary system that has been classified as a Maia variable candidate. These objects are pulsators that apparently lie outside the theoretical instability strips. Aims. We determine the properties of V424 Cep and identify the nature of the pulsating variable. Methods. We analyzed photometric data obtained over the past three decades from TESS, Gaia, Hipparcos, and ground-based observations. Times of minimum light were determined, and the light curves and spectral energy distribution were analyzed. We analyzed the radial velocity curves of the double-lined system obtained from spectroscopy at the Observatorio Astronómico Nacional on the Sierra San Pedro Mártir. Results. The two eclipses observed in the light curves yield a refined orbital period P = 4.93 d, an eccentricity e = 0.02, and an apsidal period U = 730 yr. 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 8.7 M_⊙ and 6.3 M_⊙, their radii are 6.0 R_⊙ and 3.5 R_⊙, and the luminosities are log(L/L_⊙) 3.80 and 3.11. The TESS light curve shows oscillations with a dominant period of 0.17 d. 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 21 000 K. 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. Conclusions. V424 Cep is not a Maia variable, but rather a β Cep star. This result highlights the importance of combining photometric light-curve solutions with absolute flux models and spectroscopic observations. ⋆ Based in part on observations carried out at the Observatorio Astronómico Nacional on the Sierra San Pedro Mártir (OAN-SPM), Baja California, México.