标题： xi^1 CMa的超慢自转确认：磁极性反转和磁层紫外发射线的显著变化 显示英文标题

标题： Confirmation of xi^1 CMa's ultra-slow rotation: magnetic polarity reversal and a dramatic change in magnetospheric UV emission lines

摘要： 磁性贝塔刻赤座脉动星xi^1 CMa具有任何已知磁性B型恒星中最长的自转周期。它也是唯一已知的、其磁层发射同时受自转和脉动调制的磁性B型恒星。我们在此报告在xi^1 CMa中首次明确检测到负的纵向磁场（2019年的<Bz>= -87 +/- 2 G，2020年的<Bz>= -207 +/- 3 G），以及对该恒星Halpha变化的持续监测结果。我们研究了偏离纯偶极拓扑结构的证据。我们还报告了一次在磁性零点附近获得的xi^1 CMa新的HST紫外光谱，该光谱与在最大发射附近获得的贝塔刻赤座的紫外光谱相似，表明其提供了磁层的赤道视图。xi^1 CMa的新紫外光谱通过与档案数据的比较，进一步提供了该恒星极其长的自转周期的证据。 显示英文摘要

摘要： The magnetic beta Cep pulsator xi^1 CMa has the longest rotational period of any known magnetic B-type star. It is also the only magnetic B-type star with magnetospheric emission that is known to be modulated by both rotation and pulsation. We report here the first unambiguous detection of a negative longitudinal magnetic field in xi^1 CMa (<Bz>=-87 +/- 2 G in 2019 and <Bz>=-207 +/- 3 G in 2020), as well as the results of ongoing monitoring of the star's Halpha variability. We examine evidence for deviation from a purely dipolar topology. We also report a new HST UV spectrum of xi^1 CMa obtained near magnetic null that is consistent with an equatorial view of the magnetosphere, as evidenced by its similarity to the UV spectrum of beta Cep obtained near maximum emission. The new UV spectrum of xi^1 CMa provides additional evidence for the extremely long rotation period of this star via comparison to archival data.