The Double-lined Eclipsing γ Doradus System AX Draconis in a 0.568 day Orbit

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Abstract For the near-contact binary AX Dra, we present the first time-series spectroscopy collected with the echelle spectrograph BOES. From spectral analysis, we measured the projected rotation of v 1 sin i = 120 ± 21 km s −1 and effective temperature of T eff,1 = 7220 ± 150 K for the brighter primary component, together with radial velocities (RVs) for both stars. To obtain a consistent binary model, the RV curves were analyzed by combining the 2 minute cadence photometric data observed in the TESS sectors 15, 21, 22, and 41. The modeling indicates that AX Dra is a semi-detached system exhibiting a total secondary eclipse, with the detached primary component having a large filling factor of 92%. The system has masses of 1.717 ± 0.026 M ⊙ and 0.804 ± 0.014 M ⊙ , radii of 1.541 ± 0.020 R ⊙ and 1.237 ± 0.014 R ⊙ , luminosities of 5.78 ± 0.50 L ⊙ and 0.83 ± 0.05 L ⊙ , and a temperature difference of Δ( T eff,1 – T eff,2 ) = 2263 ± 163 K. Multifrequency analyses of the TESS residual lights yielded 35 significant signals in the frequency range below 5 day −1 . Among them, four frequencies of f 1 , f 2 , f 3 , and f 5 are independent γ Dor pulsations of the primary star, for which two acceptable mode-identification solutions were obtained using the frequency ratio method. These results suggest that AX Dra is the shortest-period double-lined eclipsing binary containing a γ Dor-type pulsator and that the pulsating primary is likely an accretor affected by mass transfer.

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