论文标题

主要的Corot目标HD43587是否在最低阶段?

Is the primary CoRoT target HD43587 under a Maunder minimum phase?

论文作者

Ferreira, Rafael Ramon, Barbosa, Rafaella, Castro, Matthieu, Guerrero, Gustavo, de Almeida, Leandro, Boumier, Patrick, Nascimento Jr, José Dias do

论文摘要

与太阳能活动相关的最神秘的现象之一是所谓的Maunder最低阶段。它由有史以来最低的太阳生物注册为太阳的人数组成,到目前为止,其他恒星还没有证实。由于对威尔逊山天文台的恒星活性的光谱观察结果,太阳能模拟HD43587显示出非常低且显然是不变的活性水平,这使其成为最低限度的候选者。我们分析了HD43587及其进化状态的色球活性演化,旨在揭示这种低和平坦活性的原因。我们使用文献中可用的活动测量数据集,并计算竖琴和纳瓦尔光谱的活动S指数,以推断一个周期。此外,我们分析了HD43587的Corot灯曲线,并应用陀螺仪和活性校准以确定其旋转周期。最后,基于进化模型和推断的旋转期,我们使用Eulag-MHD代码执行HD43587的全局MHD模拟,以便获得有关其发电机过程的一些见解。我们确认了几乎平坦的活动轮廓,其中一个周期期$ p _ {\ mathrm {cyc}} = 10.44 \ pm3.03 $ yrs从S-索引时间序列中得出,并且长期趋势可能大于50年。不可能从光曲线定义一个旋转周期,但是陀螺仪和活动校准允许推断$ \ overline {p} _ {\ mathrm {rot}} = 22.6 \ pm 1.9 $ d的间接估计。此外,MHD模拟证实了一个振动性发电机,其周期周期与观测值和低表面磁性活性水平非常吻合。我们得出的结论是,由于其年龄,该对象可能正在磁性活动的“自然”减少。然而,不能排除HD43587处于最低阶段的可能性。

One of the most enigmatic phenomena related to solar activity is the so-called Maunder minimum phase. It consists of the lowest sunspot's counting ever registered for the Sun, and never so far confirmed for other stars. Since the spectroscopic observations of stellar activity at the Mount Wilson Observatory, the solar analog HD43587 has shown a very low and apparently invariant activity level, which makes it a Maunder minimum candidate. We analyze the chromospheric activity evolution of HD43587 and its evolutive status, intending to unravel the reasons for this low and flat activity. We use an activity measurements dataset available in the literature, and compute the activity S-index from HARPS and NARVAL spectra, to infer a cycle period. Besides, we analyze the CoRoT light-curve of HD43587, and apply gyrochronology and activity calibrations, to determine its rotation period. Finally, based on an evolutionary model and the inferred rotation period, we use the EULAG-MHD code to perform global MHD simulations of HD43587 with the aim of getting some insights about its dynamo process. We confirm the almost flat activity profile, with a cycle period $P_{\mathrm{cyc}} = 10.44\pm3.03$ yrs deduced from the S-index time series, and a long-term trend that might be a period larger than 50 yrs. It was impossible to define a rotation period from the light-curve, however gyrochronology and activity calibrations allow to infer an indirect estimate of $\overline{P}_{\mathrm{rot}} = 22.6 \pm 1.9$ d. Furthermore, the MHD simulations confirm an oscillatory dynamo with a cycle period in good agreement with the observations and a low level of surface magnetic activity. We conclude that this object might be experiencing a "natural" decrease in magnetic activity as a consequence of its age. Nevertheless, the possibility that HD43587 is in a Maunder minimum phase cannot be ruled out.

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