Physical Nature of the Eclipsing δ Scuti Star AO Serpentis

Abstract

We present the absolute properties of the eclipsing binary AO Ser with a pulsating component from our $BV$ photometric and high-resolution spectroscopic observations, which were performed between April and May 2017. The radial velocities (RVs) for both components were measured, and the effective temperature and projected rotational velocity of the primary star were determined to be $T_{\mathrm{eff},1}$ = 8,820 $\pm$ 62 K and $v_1\sin i_1$ = 90 $\pm$ 18 km s${}^{-1}$, respectively, by comparing the observed spectrum with the Kurucz models. The accurate fundamental parameters of AO Ser were determined by a simultaneous analysis of the light and RV curves. The masses and radii of the primary and secondary components are $M_1$ = 2.55 $\pm$ 0.09 M${}_{\odot }$ and $R_1$ = 1.64 $\pm$ 0.02 R${}_{\odot }$ and $M_2$ = 0.49 $\pm$ 0.02 M${}_{\odot }$ and $R_2$ = 1.38 $\pm$ 0.02 R${}_{\odot }$, respectively. Multiple frequency analyses for the eclipse-subtracted light residuals were conducted. As a result, we detected two frequencies of $f_1$ = 21.852 days${}^{-1}$ and $f_2$ = 23.484 days${}^{-1}$. The evolutionary position on the HR diagram and the pulsational characteristics indicate that the primary star is a $\hat{I}´$ Sct pulsator with a radial fundamental mode. On the other hand, the relatively evolved secondary is oversized for its own mass.

19 pages, including 7 figures and 3 tables, accepted for publication in AJ