Abstract We utilize the PAdova and TRieste Stellar Evolution Code (PARSEC) combined with photometric observations to determine a guaranteed mass of AL Cas and re-examine its related physical parameters. Multicolor-photometric observations of AL Cas have been performed in 2016 and 2017. We use the Wilson-Devinney (W-D) code to analyze the light curves and find that AL Cas is probably an A-subtype contact binary (f = 35.7±0.9%) with a mass ratio q = 0.6399±0.0230 and an effective temperature difference ∆T = 78 K. The mass-radius relation of a higher luminosity component for AL Cas is obtained by two methods: depending on calculation of the Roche lobe (DCRL method) and depending on calculation of the W-D code (DCWD method). Using this relationship with the PARSEC model, we investigate the component masses of AL Cas as M1 = 1.19±0.23 M⊙ with M2 = 0.76±0.18 M⊙ by the DCRL method and M1 = 1.22±0.26 M⊙ with M2 = 0.78±0.20 M⊙ by the DCWD method. By means of the photometric studies, we examine the related physical properties of AL Cas with the latest findings. We update the orbital period (Porb = 0.50055593 d) of AL Cas according to six new times of light minimum together with those collected from the literature. Meanwhile, the (O − C)2 curve analysis suggests that the orbital period of AL Cas has a cyclic variation with a period of 81.25 yr and an amplitude of 0.01415 d. This cyclic change would be caused by the light-travel time effect from a third body. A similar mass of the third body (M3 sin i′ = 0.279 M⊙) is derived from our two methods.
Keywords stars: binaries: close — stars: binaries: eclipsing — stars: individual: AL Cassiopeiae
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