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arXiv 1608.05403astro-ph.SRastro-ph.IM
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长周期造父变星周-周调制谱线变率和速度变率的发现

Discovery of Cycle-to-cycle Modulated Spectral Line Variability and Velocity Gradients in Long-period Cepheids

Richard I. Anderson

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17 pages, 14 figures, 4 tables, MNRAS accepted
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摘要：

这项工作报告了周期到周期调制的谱线和大气速度梯度变化的发现，在长周期造父变星的基础上925高分辨率光谱的$\ell$船底座（P $\sim$ 35.5 d）在三个重型周期监测活动（2014年，2015年和2016年）记录。谱线的变异性研究通过交叉关联函数（CCF）计算使用三套谱线（弱，太阳，强）。金属线速度梯度δv $_r$（t）被计算为弱线RV和强线RV之间的差。CCF形状指示器BIS（不对称性）、FWHM和深度都表现出明显的相位相关变化模式，这些模式从一个脉动周期到下一个脉动周期都不同。弱线CCF比强线CCF更明显地表现出这些效应。BIS表现出最奇特的调制可变性，并可用于识别周期到周期调制线轮廓变化的存在。δv $_r$（t）清楚地显示出与调制BIS变率密切相关的周间差异，表明大气速度场的扰动是调制谱线变率的原因。这些扰动在收缩期间最显著，并且与脉动不同相，在连续的脉动周期之间传递信息。这项工作表明RV曲线调制是大气速度梯度扰动的结果。这些扰动的可能起源和它们对造父变星RV测量的影响，以及用于Baade-Wesselink型距离测定的投影因子进行了讨论。

英文摘要：

This work reports the discovery of cycle-to-cycle modulated spectral line and atmospheric velocity gradient variability in long-period Cepheids based on 925 high-resolution optical spectra of $\ell$ Carinae (P $\sim$ 35.5 d) recorded during three heavy duty-cycle monitoring campaigns (in 2014, 2015, and 2016). Spectral line variability is investigated via cross-correlation functions (CCFs) computed using three sets of spectral lines (weak, solar, strong). A metallic line velocity gradient, δv$_r$ (t), is computed as the difference between weak and strong-line RVs. CCF shape indicators BIS (asymmetry), FWHM, and depth all exhibit clear phase-dependent variability patterns that differ from one pulsation cycle to the next. Weak-line CCFs exhibit these effects more clearly than strong-line CCFs. BIS exhibits the most peculiar modulated variability and can be used to identify the presence of cycle-to-cycle modulated line profile variations. δv$_r$ (t) clearly exhibits cycle-to-cycle differences that correlate very closely with modulated BIS variability, suggesting perturbations of the atmospheric velocity field as the cause for modulated spectral line variability. These perturbations are most significant during contraction and are not in phase with the pulsation, transmitting information between consecutive pulsation cycles. This work shows RV curve modulation to be a consequence of atmospheric velocity gradient perturbations. Possible origins of these perturbations and their impact on Cepheid RV measurements as well as the projection factor used in Baade-Wesselink-type distance determinations are discussed.

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