Abstract

Ap stars are chemically peculiar, main-sequence stars with atmospheres having an anomalous chemical composition (compared to the solar one). This abnormal chemical composition is thought to result from diffusion of chemical elements under the influence of radiation pressure and gravitational settling. Depending on the prevailing process, a chemical element either sinks and is accumulated in deeper layers or floats up to the upper layers of the stellar atmosphere. In addition to nonuniform depth distributions of elements, peculiar stars feature spots on their surface enriched or depleted with certain chemical elements. Ap stars have strong global magnetic fields with intensities ranging from several hundred millitesla to several tesla. These fields, as a rule, have a simple dipole configuration that remains stable over time intervals of several decades at the least. One of the unexplored effects observed in chemically peculiar stars is the significant difference in magnetic fields measured using different spectral lines. The present study is focused on measurements of the longitudinal magnetic field of the chemically peculiar Ap star 33 Lib in N = 180 spectral lines. High-resolution circularly polarized spectra collected over four nights in 2006 with the 3.6 m CFHT ESPaDOnS spectrograph were taken from the CADC open database. The magnetic field was calculated based on the Zeeman effect using the single-line method. It was found that the longitudinal magnetic field of 33 Lib averaged over all nights is 〈B_e〉 = 274.9 ± 2.7 mT. Statistically significant differences between the magnetic-field magnitudes determined for different spectral lines (including those of the same chemical element) were also found. The weakest magnetic field was measured in the cores of hydrogen lines H_α and H_β and in Y and Pr lines. The dependence of the magnetic-field magnitude on parameters of spectral lines revealed that weak lines with small Lande factors had the strongest magnetic field. This may be attributed to the nonuniformity of the magnetic field in the stellar atmosphere and the distribution of chemical elements over the surface (and/or with depth) or to both these factors.

中文翻译：

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Ap Star 33 Lib的磁场：不同谱线的研究

摘要

恒星是化学特有的主序恒星，大气中的化学成分异常（与日照恒星相比）。这种异常的化学组成被认为是由于化学元素在辐射压力和重力沉降的影响下的扩散所致。根据当前的过程，化学元素会下沉并积聚在更深的层中，或者会向上漂浮到恒星大气的上层。除了元素的深度分布不均匀以外，奇特的恒星在其表面还具有富集或贫乏某些化学元素的斑点。Ap星具有强大的全球磁场，强度范围从几百毫特斯拉到几特斯拉。这些字段通常是 具有简单的偶极子配置，至少在几十年的时间间隔内保持稳定。在化学特有恒星中观察到的未探索效应之一是使用不同谱线测得的磁场的显着差异。本研究集中在测量化学特有的Ap star 33 Lib的纵向磁场。N = 180条光谱线。2006年用3.6 m CFHT ESPaDOnS光谱仪采集的高分辨率圆偏振光谱是从CADC开放数据库中采集的，该光谱图是在2006年的四个晚上进行的。使用单线方法基于塞曼效应来计算磁场。发现整夜平均33 Lib的纵向磁场为< B _e＞ = 274.9±2.7 mT。还发现了针对不同光谱线（包括相同化学元素的光谱线）确定的磁场强度之间的统计显着差异。最弱的磁场在氢气线的芯测量ħ _α和ħ _β并在Y和Pr行中。磁场强度对谱线参数的依赖性表明，具有较小兰德因子的弱线具有最强的磁场。这可能归因于恒星大气中磁场的不均匀性以及化学元素在表面（和/或深度）上的分布，或者归因于这两个因素。