Magnetic field and atmospheric chemical abundances of the magnetic Ap star HD 318107
Magnetic field and atmospheric chemical abundances of the magnetic Ap star HD 318107
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磁 Ap 星 HD 318107 的磁场和大气化学丰度
DOI：
10.1051/0004-6361/201117856
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发表时间：
2011
影响因子：
6.5
通讯作者：
Bailey J
中科院分区：
文献类型：
--
作者：
Bailey J
新一代强大而有效的分光偏振仪最近被用来提供第一个精确已知年龄的磁性Ap星样本。这些数据的建模提供了对这些非凡恒星的物理和主序列演化的重要新见解的可能性。目的用ESPaDOnS分光偏振仪获得了新的光谱，并补充了来自ESO UVES，UVES-FLAMES和HARPS摄谱仪的非偏振光谱，这是一颗非常奇特的大磁场Ap星星HD 318107，它是疏散星团NGC 6405的成员，因此是一颗年龄确定的星星。现有的数据提供了足够的材料，重新分析的一阶模型的磁场的几何形状，并获得化学丰度的Si，Ti，Fe，Nd，Pr，Mg，Cr，Mn，O，和Ca.MethodsThe模型得到使用ZEEMAN，一个程序，合成的光谱线轮廓的恒星，磁场。的磁场结构建模与低阶共线多极展开，使用来自所观察到的磁场强度与旋转相位的变化的系数。几种元素的丰度是用光谱合成法测定的。经过实验与一个非常简单的模型上的每个三个环的宽度相等的共同纬度和对称的假设磁轴的均匀丰度，我们决定建立模型的光谱假设均匀丰度的每个元素在恒星surface.ResultsThe新的磁场测量使我们能够完善的旋转周期HD 318107 toP= 9.7088 ± 0.0007天。适当的磁场模型参数被发现，非常粗略地描述（显然相当复杂）的场矩变化。光谱合成导致推导出元素Mg，Si，Ca，Ti，Cr，Fe，Nd和Pr的平均丰度。除了Mg和Ca之外，所有这些元素与太阳丰度比相比都非常丰富。有相当多的证据表明，非均匀性，例如在不同的价值观，发现使用线的不同elements.ConclusionsThe目前的数据集，而有限的，但足以提供一个有用的一阶评估的磁性和表面丰度属性的HD 318107，这使得它成为少数几颗已知年龄的磁性Ap星之一，这两种性质都被研究过。
ContextA new generation of powerful and efficient spectropolarimeters has recently been used to provide the first sample of magnetic Ap stars of accurately known ages. Modelling of these data offer the possibility of significant new insights into the physics and main sequence evolution of these remarkable stars.AimsNew spectra have been obtained with the ESPaDOnS spectropolarimeter, and are supplemented with unpolarised spectra from the ESO UVES, UVES-FLAMES, and HARPS spectrographs, of the very peculiar large-field magnetic Ap star HD 318107, a member of the open cluster NGC 6405 and thus a star with a well-determined age. The available data provide sufficient material with which to re-analyse the first-order model of the magnetic field geometry and to derive chemical abundances of Si, Ti, Fe, Nd, Pr, Mg, Cr, Mn, O, and Ca.MethodsThe models were obtained using ZEEMAN, a program which synthesises spectral line profiles for stars that have magnetic fields. The magnetic field structure was modelled with a low-order colinear multipole expansion, using coefficients derived from the observed variations of the field strength with rotation phase. The abundances of several elements were determined using spectral synthesis. After experiments with a very simple model of uniform abundance on each of three rings of equal width in co-latitude and symmetric about the assumed magnetic axis, we decided to model the spectra assuming uniform abundances of each element over the stellar surface.ResultsThe new magnetic field measurements allow us to refine the rotation period of HD 318107 toP= 9.7088 ± 0.0007 days. Appropriate magnetic field model parameters were found that very coarsely describe the (apparently rather complex) field moment variations. Spectrum synthesis leads to the derivation of mean abundances for the elements Mg, Si, Ca, Ti, Cr, Fe, Nd, and Pr. All of these elements except for Mg and Ca are strongly overabundant compared to the solar abundance ratios. There is considerable evidence of non-uniformity, for example in the different values of ⟨Bz⟩ found using lines of different elements.ConclusionsThe present data set, while limited, is nevertheless sufficient to provide a useful first-order assessment of both the magnetic and surface abundance properties of HD 318107, making it one of the very few magnetic Ap stars of well-known age for which both of these properties have been studied.
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