昴星团中超级耀斑的同时Kepler/K2和XMM-网络观测
Simultaneous Kepler/K2 and XMM-Netwon observations of superflares in the Pleiades
摘要：
耀斑是由磁能的突然释放所引发的强烈事件。为了研究同时在光学和X射线光下观察到的昴星团中1.25亿年前恒星的耀斑，我们在开普勒K2 Campaign 4的观测期间获得了该星团的新XMM-牛顿观测。我们的目标是描述在这两个波段观察到的最强大的耀斑，并限制在光学和X射线中释放的能量，环的几何形状，以及它们的时间演化。我们的目标是将我们的结果与现有的太阳和恒星在不同年龄发生的耀斑研究进行比较。我们选择了明亮的X射线/光学耀斑发生在12个已知的成员的昴星团从他们的K2和XMM牛顿光变曲线。样本包括10颗K-M星，一颗F9星和一颗G8星。通过对耀斑期间光变曲线的综合分析获得了耀斑的平均特性。时间分辨的X射线光谱分析的等离子体在磁回路中的时间演化的约束。在这项研究中，大多数耀斑都是以光学形式发射的能量多于X射线形式，就像大多数太阳耀斑一样，尽管昴星团耀斑以X射线形式发射的能量在其总能量中所占的比例比典型的太阳耀斑要大。此外，两个频带中的能量预算弱相关。我们还在光学和X射线中发现了可比的耀斑持续时间，并观察到快速旋转的恒星（例如，自转周期短于0.5天）优先承载短耀斑。我们估计了耀斑冷却路径在log（EM）-versus-log（T）平面上的斜率。我们得到的值是受很大的不确定性，但他们的名义值表明，耀斑在本文中分析的主要是由于单回路没有持续加热发生在冷却阶段。我们还观察和分析了一次耀斑期间周期为500 s的振荡。
英文摘要：
Flares are powerful events ignited by a sudden release of magnetic energy. With the aim of studying flares in the 125-Myr-old stars in the Pleiades observed simultaneously in optical and X-ray light, we obtained new XMM-Newton observations of this cluster during the observations of Kepler K2 Campaign 4. Our objective is to characterize the most powerful flares observed in both bands and to constrain the energy released in the optical and X-ray, the geometry of the loops, and their time evolution. We aim to compare our results to existing studies of flares occurring in the Sun and stars at different ages. We selected bright X-ray/optical flares occurred in 12 known members of the Pleiades from their K2 and XMM-Newton light curves. The sample includes ten K-M stars, one F9 star, and one G8 star. Flare average properties were obtained from integrated analysis of the light curves during the flares. The time evolution of the plasma in the magnetic loops is constrained with time-resolved X-ray spectral analysis. Most of the flares studied in this work emitted more energy in optical than in X-rays, as in most solar flares, even if the Pleiades flares output a larger fraction of their total energy in X-rays than typical solar flares do. Additionally, the energy budget in the two bands is weakly correlated. We also found comparable flare duration in optical and X-rays and observed that rapidly rotating stars (e.g., with rotation period shorter than 0.5 days) preferentially host short flares. We estimated the slope of the cooling path of the flares in the log(EM)-versus-log(T) plane. The values we obtained are affected by large uncertainties, but their nominal values suggest that the flares analyzed in this paper are mainly due to single loops with no sustained heating occurring during the cooling phase. We also observed and analyzed oscillations with a period of 500 s during one of the flares.
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