Probing the dynamical structure of δ Cephei atmosphere
Probing the dynamical structure of δ Cephei atmosphere
复制标题
探索仙王δ大气的动力结构
DOI：
--
复制
发表时间：
2006
期刊：
影响因子：
--
通讯作者：
P. Mathias
中科院分区：
文献类型：
--
作者：
N. Nardetto;A. Fokin;D. Mourard;P. Mathias
上下文临边暗化和投影因子是目前干涉Baade-Wesselink造父变星测距方法的两个限制因素。目标。我们首先量化的相位依赖的临边暗化的派生距离的影响。然后，我们研究了一种新的方法来探测造父变星的大气动力学结构，通过光谱干涉观测。方法.本文用δ Cep流体动力学模型导出了连续谱和不同谱线上的星盘强度分布，以及相应的波长和相位相关的可见度曲线。结果我们发现，考虑到一个恒定的肢体变暗在可见光导致系统的相移约0.02的角直径曲线。但是，导出的距离不受此效应的影响。否则，对于可见光中R = 12000的光谱分辨率，我们发现在最有利的情况下（最大收缩速度），可见度曲线上的签名约为7%，这是清楚地检测到当前的光谱干涉仪。然而，投影因子对可见度曲线的影响仅为1%（或更少）。结论.光谱干涉法提供了造父变星大气层的新几何视图。然而，现在需要结合不同的技术（高分辨率光谱，光谱和差分干涉）来有效地限制造父变星大气的物理参数，特别是投影因子。
Context. Limb darkening and the projection factor are currently two limiting aspects of the interferometric Baade-Wesselink method of Cepheid distance determination. Aims. We first quantify the impact of the phase dependence of limb darkening on the derived distance. We then study a new way to probe the dynamical structure of Cepheid’s atmosphere through spectro-interferometric observations. Methods. A hydrodynamical model of δ Cep is used to derive stellar disk intensity distribution in the continuum and in different spectral lines, together with the corresponding wavelength- and phase-dependent visibility curves. Results. We find that considering a constant limb darkening in the visible leads to a systematic shift of about 0.02 in phase on the angular diameter curve. The derived distance is, however, not affected by this effect. Otherwise, for a spectroscopic resolution of R = 12 000 in the visible, we find in the most favourable case (maximum contraction velocity) a signature on the visibility curve of about 7% that is clearly detectable by current spectro-interferometers. Nevertheless, the projection factor has only a 1% (or less) effect on the visibility curve. Conclusions. The spectro-interferometry provides a new geometric view of Cepheid’s atmosphere. However, the combination of different techniques (high resolution spectroscopy, spectro- and differential-interferometry) are now needed to efficiently constrain the physical parameters of Cepheids’ atmosphere and, in particular the projection factor.