直接探测单个M巨星EK光球层中的磁场布：M巨星中的磁场活动有多普遍？
Direct detection of a magnetic field in the photosphere of the single M giant EK Boo: How common is magnetic activity among M giants?
摘要：
我们研究了快速旋转的M5巨星EKBoo，通过分光偏振法获得直接和同时测量的磁场和活动指标，以推断在这个相当进化的巨人活动的起源。我们使用了新的分光偏振计NARVAL在伯纳德Lyot望远镜（天文台杜Pic杜Midi，法国）获得了一系列的斯托克斯我和斯托克斯V配置文件的EK布。使用最小二乘反卷积技术，我们能够检测到塞曼签名的磁场。我们通过平均的Stokes V和Stokes I剖面测量了它的纵向分量。光谱还允许我们监测CaII K&H色球发射线，这是众所周知的恒星磁活动的指标。从2008年4月至2009年3月间获得的10次观测结果中，我们推断EK Boo具有磁场，其变化范围为-0.1至-8 G。根据最新的恒星演化轨迹，我们还确定了EKBoo的初始质量和演化阶段。初始质量在2.0-3.6 M太阳的范围内，EKBoo要么在渐近巨星分支（AGB）上，要么在热脉冲阶段的开始，要么在第一个（或红）巨星分支（RGB）的尖端。EKBoo的快速旋转和活动可能是由从内部挖掘的角动量或合并的双星解释的。此外，我们还观察到了另外八颗M巨星，它们被称为X射线发射体，或者在它们的类别中旋转得很快。对于其中的一颗，β-And，大概也是一颗AGB星，我们有一个边缘检测的磁场，和一个纵向分量B1约1G的测量。更多这样的观测将回答这样一个问题，即EK Boo是否是一个特例，或者磁性活动在M巨星中是否比预期的更普遍。
英文摘要：
We study the fast rotating M5 giant EK Boo by means of spectropolarimetry to obtain direct and simultaneous measurements of both the magnetic field and activity indicators, in order to infer the origin of the activity in this fairly evolved giant. We used the new spectropolarimeter NARVAL at the Bernard Lyot Telescope (Observatoire du Pic du Midi, France) to obtain a series of Stokes I and Stokes V profiles for EK Boo. Using the Least Square Deconvolution technique we were able to detect the Zeeman signature of the magnetic field. We measured its longitudinal component by means of the averaged Stokes V and Stokes I profiles. The spectra also permitted us to monitor the CaII K&H chromospheric emission lines, which are well known as indicators of stellar magnetic activity. From ten observations obtained between April 2008 and March 2009, we deduce that EK Boo has a magnetic field, which varied in the range of -0.1 to -8 G. We also determined the initial mass and evolutionary stage of EK Boo, based on up-to-date stellar evolution tracks. The initial mass is in the range of 2.0-3.6 M_sun, and EK Boo is either on the asymptotic giant branch (AGB), at the onset of the thermal pulse phase, or at the tip of the first (or red) giant branch (RGB). The fast rotation and activity of EK Boo might be explained by angular momentum dredge-up from the interior, or by the merging of a binary. In addition, we observed eight other M giants, which are known as X-ray emitters, or to be rotating fast for their class. For one of these, beta And, presumably also an AGB star, we have a marginal detection of magnetic field, and a longitudinal component Bl of about 1G was measured. More observations like this will answer the question whether EK Boo is a special case, or whether magnetic activity is, rather, more common among M giants than expected.
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。
