2026ApJ...997....6Z

AY Gem is a short-period Algol-type eclipsing binary with a period of 3.05 days that is neglected for spectroscopic and photometric investigations. The first radial-velocity curves have been obtained for AY Gem by using LAMOST medium- and low-resolution spectra together with the BFOSC spectral data observed with the 2.16 m telescope in Xinglong station. It is detected that AY Gem is a double-lined spectroscopic binary with an extremely low mass ratio of q = 0.10 ± 0.02. Photometric solutions derived by using the TESS data reveal that it is a semidetached binary, and the absolute parameters were determined to be: M₁ = 2.02 ± 0.05 M_⊙, M₂ = 0.19 ± 0.02 M_⊙; R₁ = 1.91 ± 0.03 R_⊙, R₂ = 2.37 ± 0.07 R_⊙. By analyzing the O-C diagram, it is found that the orbital period is decreasing continuously, which can be explained as nonconservative mass transfer with a mass-loss rate of $\dot{M}\sim -1{0}^{-9}\,{M}_{\odot }\cdot {\mathrm{yr}}^{-1}$. Meanwhile, it is discovered that AY Gem exhibits a distinct double-peaked H_α emission line, indicating the presence of a transient disk. This is further supported by the measurement of the equivalent width and the q-r diagram. Furthermore, the primary component is identified as a δ Scuti-type star that pulsates at f18 = 11.29511 days^–1 and f19 = 11.37374 days^–1. These results suggest that AY Gem is a good astrophysical laboratory for investigating mass transfer and loss, binary evolution, and the effect of tidal forces and mass accretion on stellar pulsations.