斯隆数字巡天探测到的富氢磁性白矮星的分析
Analysis of hydrogen-rich magnetic white dwarfs detected in the Sloan Digital Sky Survey
摘要：
我们在SDSS中模拟了富氢白矮星的表面磁场结构。我们计算了富氢磁白矮星的理论光谱网格，其磁场强度在1 MG和1200 MG之间，不同的角度，有效温度在7000 K和50000 K之间。我们使用了最小二乘最小化方案与进化算法，以找到最佳拟合观测数据的磁场几何形状。我们使用简单的中心偶极子或沿偶极子轴移动的偶极子来模拟每个对象的共同添加的SDSS光纤光谱。我们已经分析了所有已知的磁DA从SDSS（97个以前出版的加上44个新发现的）的光谱，并调查了该样品的磁场几何形状的统计特性。已知的磁性白矮星的总数已经比SDSS增加了三倍多，并且通过更系统的搜索预计会有更多的物体。磁场的范围介于~1和900 MG之间。我们的研究结果进一步支持了这样的说法，即Ap/Bp人口是不够的，在产生所观察到的MWD的数量和场强分布，或者另一个来源的祖类型或二进制的进化是必要的。此外，在约50%的天体中存在明显的非中心偶极子迹象，这与在Ap/Bp星中观察到的磁场分布一致。
英文摘要：
We model the structure of the surface magnetic fields of the hydrogen-rich white dwarfs in the SDSS. We have calculated a grid of state-of-the-art theoretical optical spectra of hydrogen-rich magnetic white dwarfs with magnetic field strengths between 1 MG and 1200 MG for different angles, and for effective temperatures between 7000 K and 50000 K. We used a least-squares minimization scheme with an evolutionary algorithm in order to find the magnetic field geometry best fitting the observed data. We used simple centered dipoles or dipoles which were shifted along the dipole axis to model the coadded SDSS fiber spectrum of each object. We have analysed the spectra of all known magnetic DAs from the SDSS (97 previously published plus 44 newly discovered) and also investigated the statistical properties of magnetic field geometries of this sample. The total number of known magnetic white dwarfs already more than tripled by the SDSS and more objects are expected from a more systematic search. The magnetic fields span a range between ~1 and 900 MG. Our results further support the claim that Ap/Bp population is insufficient in generating the numbers and field strength distributions of the observed MWDs, and either another source of progenitor types or binary evolution is needed. Moreover clear indications for non-centered dipoles exist in about ~50% of the objects which is consistent with the magnetic field distribution observed in Ap/Bp stars.
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