[论文解读] The field high-amplitude SX Phe variable BL Cam: results from a multisite photometric campaign. II. Evidence of a binary - possibly triple - system

S. Fauvaud, J. P. Sareyan+46 more|arXiv (Cornell University)|Apr 16, 2010

Stellar, planetary, and galactic studies参考文献 5被引用 10

一句话总结

本研究基于多站点观测的BL Camelopardalis星场高振幅SX Phe变星的测光光 light curves，检测到其最大亮度时刻的观测减计算（O-C）时间存在显著偏差。这些变化被解释为存在双星或三合星系统的证据，其中144.2天的短期调制表明存在一颗质量为0.46–1 M☉、距离约0.7 AU的致密伴星，而约3400天的长期调制则暗示可能存在一颗质量至少为0.03 M☉的棕矮星伴星，轨道半长轴约为4.5 AU，同时观测到脉动周期以(161 ± 3) × 10⁻⁹ yr⁻¹的速率持续增加。

ABSTRACT

Short-period high-amplitude pulsating stars of Population I ($δ$ Sct stars) and II (SX Phe variables) exist in the lower part of the classical (Cepheid) instability strip. Most of them have very simple pulsational behaviours, only one or two radial modes being excited. Nevertheless, BL Cam is a unique object among them, being an extreme metal-deficient field high-amplitude SX Phe variable with a large number of frequencies. Based on a frequency analysis, a pulsational interpretation was previously given. aims heading (mandatory) We attempt to interpret the long-term behaviour of the residuals that were not taken into account in the previous Observed-Calculated (O-C) short-term analyses. methods heading (mandatory) An investigation of the O-C times has been carried out, using a data set based on the previous published times of light maxima, largely enriched by those obtained during an intensive multisite photometric campaign of BL Cam lasting several months. results heading (mandatory) In addition to a positive (161 $\pm$ 3) x 10$^{-9}$ yr$^{-1}$ secular relative increase in the main pulsation period of BL Cam, we detected in the O-C data short- (144.2 d) and long-term ($\sim$ 3400 d) variations, both incompatible with a scenario of stellar evolution. conclusions heading (mandatory) Interpreted as a light travel-time effect, the short-term O-C variation is indicative of a massive stellar component (0.46 to 1 M$_{\sun}$) with a short period orbit (144.2 d), within a distance of 0.7 AU from the primary. More observations are needed to confirm the long-term O-C variations: if they were also to be caused by a light travel-time effect, they could be interpreted in terms of a third component, in this case probably a brown dwarf star ($\geq$ 0.03 \ M$_{\sun}$), orbiting in $\sim$ 3400 d at a distance of 4.5 AU from the primary.

研究动机与目标

• 研究BL Cam的O-C图中超出标准脉动模型的长期残差变化。
• 确定观测到的O-C变化是否源于双星或多合星系统的轨道运动，而非恒星内部演化所致。
• 通过光行时效应建模，约束不可见伴星的轨道参数。
• 评估BL Cam的多重性，该星为罕见的金属缺损场星SX Phe变星，具有复杂的脉动模式。

提出的方法

• 整合了来自多个站点的专业和业余观测者提供的光最大时刻的综合数据集。
• 基于稳定的脉动星历表计算出的时刻，利用观测到的最大亮度时刻构建了O-C图。
• 对O-C残差进行频率分析，以检测周期性调制，重点关注短时标和长时标信号。
• 应用光行时效应模型，将周期性O-C变化解释为不可见伴星的轨道运动。
• 在主星为脉动变星、存在两个伴星的三体系统假设下，推导出轨道参数（周期、质量函数、半振幅）。
• 利用傅里叶分析和O-C数据的误差传播，评估周期性的统计显著性。

实验结果

研究问题

• RQ1 BL Cam的长期O-C变化（超出脉动与演化效应）由何原因引起？
• RQ2 约144.2天的短期O-C调制是否可由一颗质量较大的恒星伴星引起的光行时效应解释？
• RQ3 约3400天的长期O-C变化是否与一颗位于更宽轨道上的第三颗天体（可能为棕矮星）一致？
• RQ4 BL Cam系统中假设伴星的本质及其轨道构型为何？
• RQ5 脉动周期的长期增加率(161 ± 3) × 10⁻⁹ yr⁻¹与系统的动力学有何关联？

主要发现

• 检测到周期为144.2 ± 0.02天的短期O-C变化，与一颗质量为0.46–1 M☉、距离约0.7 AU的致密伴星引起的光行时效应一致。
• 周期约为3400天（3390 ± 26 d）的长期O-C变化表明存在第二颗伴星，其质量很可能大于等于0.03 M☉，轨道半长轴约为4.5 AU，可能为棕矮星。
• 主脉动周期的长期增加率测量为(4.41 ± 0.06) × 10⁻¹⁰ d⁻¹，等价于(161 ± 3) × 10⁻⁹ yr⁻¹。
• 主星由于内层伴星引起的径向速度半振幅估计约为15 km s⁻¹，可能可通过高信噪比光谱观测探测到。
• 该系统很可能为三合星系统，内层双星具有短轨道周期，外层天体处于更长周期、可能具有偏心率的轨道上。
• 观测到的O-C变化与恒星演化模型不相容，强烈支持其起源于不可见伴星引力扰动的动力学起源。