DY Pegasi：双星系统中的一颗SX凤凰星
DY Pegasi: An SX Phoenicis Star in a Binary System with an Evolved Companion
摘要：
在这项工作中，光度数据从美国变星观测协会收集和分析的SX凤凰星DY飞马座（DY Peg）。从频率分析中，我们得到三个独立的频率：$f_0 = 13.71249\ \rm{c\ days^{-1}}$，$f_1 = 17.7000\ \rm{c\ days^{-1}}$和$f_2 =18.138\ \rm{c\ days^{-1}}$，其中$f_0$和$f_1$分别是径向基频和第一泛音模式，而$f_2$是第一次检测到的，应该属于非径向模式。最大光时的$O-C$图表明DY Peg的基本脉动模式有一个周期变化率$(1/P_0)(\mathrm{d} P_0/\mathrm{d} t) = -(5.87 \pm 0.03) \times 10^{-8} \ \mathrm{yr^{-1}}$，应该属于一个轨道周期为$P_{\mathrm{orb}} = 15425.0 \pm 205.7 \ \mathrm{days}$的双星系统。基于光谱信息，建立了单星演化模型来拟合观测到的频率。然而，拟合模型的一些重要参数与观测值不一致。结合观测和理论计算的信息，我们认为DY Peg应该是双星系统中的一颗SX型凤凰星，其质量来自于其演化的伴星（现阶段很可能是一颗热白矮星）在渐近巨星分支阶段产生的尘埃盘的残留物。这一推论还需要进一步的观测来证实，它可能是一个具有普遍意义的凤凰SX星形成机制和演化历史。
英文摘要：
In this work, the photometric data from the American Association of Variable Star Observers are collected and analyzed on the SX Phoenicis star DY Pegasi (DY Peg). From the frequency analysis, we get three independent frequencies: $f_0 = 13.71249\ \rm{c\ days^{-1}}$, $f_1 = 17.7000\ \rm{c\ days^{-1}}$, and $f_2 =18.138\ \rm{c\ days^{-1}}$, in which $f_0$ and $f_1$ are the radial fundamental and first overtone mode, respectively, while $f_2$ is detected for the first time and should belong to a nonradial mode. The $O-C$ diagram of the times of maximum light shows that DY Peg has a period change rate $(1/P_0)(\mathrm{d} P_0/\mathrm{d} t) = -(5.87 \pm 0.03) \times 10^{-8} \ \mathrm{yr^{-1}}$ for its fundamental pulsation mode, and should belong to a binary system that has an orbital period $P_{\mathrm{orb}} = 15425.0 \pm 205.7 \ \mathrm{days}$. Based on the spectroscopic information, single star evolutionary models are constructed to fit the observed frequencies. However, some important parameters of the fitted models are not consistent with that from observations. Combing with the information from observation and theoretical calculation, we conclude that DY Peg should be an SX Phoenicis star in a binary system and accreting mass from a dust disk, which was the residue of its evolved companion (most probably a hot white dwarf at the present stage) produced in the asymptotic giant branch phase. Further observations are needed to confirm this inference, and it might be potentially a universal formation mechanism and evolutionary history for SX Phoenicis stars.
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