调制RV金牛星的振幅变化支持RVb现象的尘埃遮蔽模型
Amplitude variations of modulated RV Tauri stars support the dust obscuration model of the RVb phenomenon
摘要：
上下文金牛座RV型变星是AGB后的脉动恒星，在离开渐近巨星分支后迅速演化通过不稳定带。它们的光变率主要由径向脉动控制。RVb亚类的成员表现出一种额外的变化，表现为平均亮度的长期调制，对此，最流行的理论都假设双星和某种星周尘埃。在这里，我们地址，如果振幅调制与尘埃遮蔽模型是一致的。目的。我们测量和解释的脉动沿RVb变异的平均振幅的总体变化。方法.我们汇编了RVb型恒星的长期测光数据，包括美国变星观测者协会的目视观测、OGLE和ASAS项目的地基CCD测光以及开普勒空间望远镜对天鹅座DF星的超精密空间测光。在将所有观测值转换为通量单位后，我们测量了脉动振幅的周间变化，并将它们与实际平均通量相关联。结果我们发现了一个令人惊讶的一致的脉动幅度和平均通量之间的相关性：他们的规模与彼此的线性范围很宽的通量和幅度。这意味着当相对于系统通量水平测量时，脉动幅度实际上保持恒定。在微弱状态下的明显振幅下降在文献中早已注意到，但它总是声称是难以解释的RVb现象的实际模型。在这里，我们表明，当使用通量，而不是幅度，振幅衰减是自然的解释周期性的遮蔽从一个大的不透明的屏幕，一个最有可能对应于一个环绕尘埃盘，围绕整个系统。
英文摘要：
Context. RV Tauri-type variables are pulsating post-AGB stars that evolve rapidly through the instability strip after leaving the Asymptotic Giant Branch. Their light variability is dominated by radial pulsations. Members of the RVb subclass show an additional variability in form of a long-term modulation of the mean brightness, for which the most popular theories all assume binarity and some kind of circumstellar dust. Here we address if the amplitude modulations are consistent with the dust obscuration model. Aims. We measure and interpret the overall changes of the mean amplitude of the pulsations along the RVb variability. Methods. We compiled long-term photometric data for RVb-type stars, including visual observations of the American Association of Variable Star Observers, ground-based CCD photometry from the OGLE and ASAS projects and ultra-precise space photometry of one star, DF Cygni, from the Kepler space telescope. After converting all the observations to flux units, we measure the cycle-to-cycle variations of the pulsation amplitude and correlate them to the actual mean fluxes. Results. We find a surprisingly uniform correlation between the pulsation amplitude and the mean flux: they scale linearly with each other for a wide range of fluxes and amplitudes. It means that the pulsation amplitude actually remains constant when measured relative to the system flux level. The apparent amplitude decrease in the faint states has long been noted in the literature but it was always claimed to be difficult to explain with the actual models of the RVb phenomenon. Here we show that when fluxes are used instead of magnitudes, the amplitude attenuation is naturally explained by periodic obscuration from a large opaque screen, one most likely corresponding to a circumbinary dusty disk that surrounds the whole system.
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