The Double-lined Eclipsing $\gamma$ Doradus System AX Draconis in a 0.568-day Orbit

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 $v_1\sin i$ = $120\pm 21$ km s${}^{-1}$ and effective temperature of $T_{\mathrm{eff},1}$ = $7220\pm 150$ 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-min 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 $1.717\pm 0.026$ $M_{\odot }$ and $0.804\pm 0.014$ $M_{\odot }$, radii of $1.541\pm 0.020$ $R_{\odot }$ and $1.237\pm 0.014$ $R_{\odot }$, luminosities of $5.78\pm 0.50$ $L_{\odot }$ and $0.83\pm 0.05$ $L_{\odot }$, and a temperature difference of $\Delta$($T_{\mathrm{eff},1}$--$T_{\mathrm{eff},2}$) = $2263\pm 163$ K. Multi-frequency 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 $\gamma$ 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 $\gamma$ Dor-type pulsator and that the pulsating primary is likely an accretor affected by mass transfer.

21 pages, including 6 figures and 7 tables, accepted for publication in AJ