arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2303.01033astro-ph.SRastro-ph.HE
收藏

一头扎进了地球的磁层?p星形HD108

Diving into the magnetosphere of the Of?p star HD108

Gregor Rauw, Yaël Nazé, Asif ud-Doula, Coralie Neiner

摘要:

我们分析光学和X射线光谱的?p星HD 108,以其强偶极磁场和光学线轮廓变化而闻名,时间尺度为$54 \pm 3$ yrs,解释为恒星自转周期。光发射谱线现在已经从2007 - 2008年达到的最低发射状态恢复。H $α$发射的等效宽度的变化提供了对旋转轴的倾斜度($i$)和磁轴的倾斜度($β$)的约束。模型和观测之间的最佳协议被发现为($i$,$β$)与$i + β\simeq 85^{\circ}$和$i \in [30^{\circ},55^{\circ}]$对。巴耳末发射谱线在几天的时间尺度上在$\sim 5$ %水平上显示随机变化。TESS测光揭示了除了突出的红噪声变化之外,在类似时间尺度上的瞬态调制。2021年12月的钱德拉X射线观测表明,与2002年8月的XMM-牛顿观测相比,该恒星处于更高的发射水平,通量略有增加,光谱硬化,接近最小发射状态。磁流体动力学模拟用于计算合成X射线光谱。利用我们目前对$\dot{M}_{B=0}$质量损失率的最佳估计,模拟的X射线光度和光谱能量分布与观测结果非常吻合。最后,径向速度的变化周期为8.5年,峰-峰幅度为10 - 11公里/秒$^{-1}$,表明轨道运动至少有一个看不见的伴星$_{\odot}$。

英文摘要:

We analyse optical and X-ray spectroscopy of the Of?p star HD108, known for its strong dipolar magnetic field and its optical line profile variability with a timescale of $54 \pm 3$ yrs, interpreted as the stellar rotation period. Optical emission lines have now recovered from their minimum emission state reached in 2007 - 2008. The variations of the equivalent width of the H$α$ emission provide constraints on the inclination of the rotation axis ($i$) and the obliquity of the magnetic axis ($β$). The best agreement between model and observations is found for ($i$, $β$) pairs with $i + β\simeq 85^{\circ}$ and $i \in [30^{\circ},55^{\circ}]$. The Balmer emission lines display stochastic variability at the $\sim 5$ % level on timescales of a few days. TESS photometry unveils transient modulations on similar timescales in addition to prominent red noise variations. A Chandra X-ray observation of December 2021, when the star was at a higher emission level, indicates a slight increase of the flux and a spectral hardening compared to the August 2002 XMM-Newton observation, taken near minimum emission state. Magnetohydrodynamic simulations are used to compute synthetic X-ray spectra. With our current best estimate of the $\dot{M}_{B=0}$ mass-loss rate, the simulated X-ray luminosity and spectral energy distribution agree very well with the observations. Finally, the radial velocities vary on a period of 8.5 years with a peak-to-peak amplitude of 10 - 11 km s$^{-1}$, suggesting orbital motion with an unseen companion of at least 4 M$_{\odot}$.

机构、总结、中文摘要均由AI分析而来,可能存在错误,请以论文正文为准。

↑