Magnetic Doppler imaging of 53 Camelopardalis in all four Stokes parameters
Magnetic Doppler imaging of 53 Camelopardalis in all four Stokes parameters
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53 只羚羊的所有四个斯托克斯参数的磁多普勒成像
DOI：
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发表时间：
2004
期刊：
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通讯作者：
T. Sigut
中科院分区：
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作者：
O. Kochukhov;S. Bagnulo;G. Wade;L. Sangalli;N. Piskunov;J. Landstreet;P. Petit;T. Sigut
我们提出了第一次调查的恒星表面磁场的结构，使用线轮廓在所有四个斯托克斯参数。我们提取的信息的磁场几何形状和丰度分布的化学奇特的星星53凸轮建模的时间序列的高分辨率光谱偏振观测的帮助下，一个新的磁多普勒成像代码。这种独特的四个斯托克斯参数数据和国家的最先进的磁成像技术相结合，使人们有可能直接从斯托克斯光谱的旋转变化推断恒星磁场拓扑结构。在53 Cam的磁成像中，我们抛弃了传统的多极假设，在Ap星的磁场结构和探索恒星的磁拓扑结构，而不引入任何全球的先验约束的场结构。用我们的磁多普勒成像方法导出的53 Cam的复磁模型与观测到的强磁敏Fe_（13）~（13）谱线的强度、圆偏振和线偏振分布都有很好的拟合。观测和模型预测之间的这种一致性对于任何早期的多极磁性模型都是不可能的，该多极磁性模型基于模拟斯托克斯I谱和拟合表面平均磁性可观测量（例如，纵向场、磁场模量等）。此外，我们证明，即使是直接反演的四个斯托克斯参数的53凸轮假设一个低阶多极磁几何是无法实现一个适当的适合我们的光谱偏振观测。因此，作为我们的调查的主要结果，我们发现，53凸轮的磁场拓扑结构是相当复杂的比任何低阶多极扩展，提出了一个普遍的问题多极假设的有效性的研究磁场结构的Ap星。除了对53 Cam的磁场进行分析外，我们还重建了Si，Ca，Ti，Fe和Nd的表面丰度分布。这些丰度图证实了以前对53 Cam的研究结果，特别是Ca和Ti丰度的显著反相变化。
We present the first investigation of the structure of the stellar surface magnetic field using line profiles in all four Stokes parameters. We extract the information about the magnetic field geometry and abundance distributions of the chemically peculiar star 53 Cam by modelling time-series of high-resolution spectropolarimetric observations with the help of a new magnetic Doppler imaging code. This combination of the unique four Stokes parameter data and state-of-the-art magnetic imaging technique makes it possible to infer the stellar magnetic field topology directly from the rotational variability of the Stokes spectra. In the magnetic imaging of 53 Cam we discard the traditional multipolar assumptions about the structure of magnetic fields in Ap stars and explore the stellar magnetic topology without introducing any global a priori constraints on the field structure. The complex magnetic model of 53 Cam derived with our magnetic Doppler imaging method achieves a good fit to the observed intensity, circular and linear polarization profiles of strong magnetically sensitive Fe spectral lines. Such an agreement between observations and model predictions was not possible with any earlier multipolar magnetic models, based on modelling Stokes I spectra and fitting surface averaged magnetic observables (e.g., longitudinal field, magnetic field modulus, etc.). Furthermore, we demonstrate that even the direct inversion of the four Stokes parameters of 53 Cam assuming a low- order multipolar magnetic geometry is incapable of achieving an adequate fit to our spectropolarimetric observations. Thus, as a main result of our investigation, we discover that the magnetic field topology of 53 Cam is considerably more complex than any low-order multipolar expansion, raising a general question about the validity of the multipolar assumption in the studies of magnetic field structures of Ap stars. In addition to the analysis of the magnetic field of 53 Cam, we reconstruct surface abundance distributions of Si, Ca, Ti, Fe and Nd. These abundance maps confirm results of the previous studies of 53 Cam, in particular dramatic antiphase variation of Ca and Ti abundances.