Mass Transfer and Loss in an Extremely Low-mass-ratio Semidetached Binary with a Pulsating A-type Star

Abstract 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: M 1 = 2.02 ± 0.05 M ⊙ , M 2 = 0.19 ± 0.02 M ⊙ ; R 1 = 1.91 ± 0.03 R ⊙ , R 2 = 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 <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mi>M</mml:mi> <mml:mo>̇</mml:mo> </mml:mover> <mml:mo>∼</mml:mo> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> <mml:msup> <mml:mn>0</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>9</mml:mn> </mml:mrow> </mml:msup> <mml:mspace width="1em"/> <mml:msub> <mml:mi>M</mml:mi> <mml:mo>⊙</mml:mo> </mml:msub> <mml:mo>·</mml:mo> <mml:msup> <mml:mi>yr</mml:mi> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msup> </mml:math> . 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 f 18 = 11.29511 days −1 and f 19 = 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.