[论文解读] The Hercules-Lyra Association revisited New age estimation and multiplicity study

T. Eisenbeiß, M. Ammler‐von Eiff+6 more|arXiv (Cornell University)|Dec 14, 2013

Stellar, planetary, and galactic studies参考文献 87被引用 24

一句话总结

本研究利用多波段观测重新审视了 Hercules-Lyra 星协（Her-Lyr），以精炼其年龄和多重性特征。通过分析锂等效宽度、X射线光度以及恒星运动学，作者推导出约250 Myr的自转年龄，并确认存在显著的锂异常分布，表明其形成历史复杂。该星协可能是一个介于昴星团与大熊座移动星群之间的中等年龄群体。

ABSTRACT

The Her-Lyr assoc., a nearby young MG, contains a few tens of ZAMS stars of SpT F to M. The existence and the properties of the Her-Lyr assoc. are controversial and discussed in the literature. The present work reassesses properties and the member list of Her-Lyr assoc., based on kinematics and age. Many objects form multiple systems or have low-mass companions and so we need to account for multiplicity. We use our own new imaging obs. and archival data to identify multiple systems. The colors and magnitudes of kinematic candidates are compared to isochrones. We derive further information on the age based on Li depletion, rotation, and coronal and chromospheric activity. A set of canonical members is identified to infer mean properties. Membership criteria are derived from the mean properties and used to discard non-members. The candidates selected from the literature belong to 35 stellar systems, 42.9% of which are multiple. Four multiple systems are confirmed in this work by common proper motion. An orbital solution is presented for the binary system HH Leo B and C. Indeed, a group of candidates displays signatures of youth. 7 canonical members are identified. The distribution of EWLi of canonical Her-Lyr members is spread widely and is similar to that of the Pleiades and the UMa group. Gyrochronology gives an age of 257+-46 Myr which is in between the ages of the Pleiades and the Ursa Major group. The measures of chromospheric and coronal activity support the young age. Four membership criteria are presented based on kinematics, EWLi, chromospheric activity, and gyro. age. In total, 11 stars are identified as certain members including co-moving objects plus additional 23 possible members while 14 candidates are doubtful or can be rejected. A comparison to the mass function, however, indicates the presence of a large number of additional unidentified low-mass members.

研究动机与目标

• 利用改进的恒星参数和自转年龄模型，重新评估 Hercules-Lyra 星协的年龄。
• 研究 Her-Lyr 成员的多重性特征，以提高恒星普查的完整性。
• 通过分析锂丰度分布，理解年轻移动星群的形成与演化过程。
• 厘清该星协与其他邻近移动星群（如 UMa、AB Dor、SACY）以及本地星协（LA）的关系。
• 通过解析成像和自行分析，解决低质量恒星及潜在棕矮星伴星的存在问题。

提出的方法

• 利用 VLT 和 Calar Alto 望远镜的高分辨率光谱观测，测量恒星参数、铁和锂的丰度。
• 应用自转年龄模型，基于恒星自转周期估算年龄，得出平均年龄约为 250 Myr。
• 分析 X 射线光度函数（LX），与昴星团比较，评估其年轻程度和活动水平。
• 构建 UV 空间图以识别非成员，并探究可能存在的更古老恒星流。
• 利用测光和天体测量数据，通过共同自行和空间同一致性，探测并确认双星和多星系统。
• 使用 SIMBAD、VizieR 和 HEASARC 数据库进行交叉识别，并整合档案数据。

实验结果

研究问题

• RQ1 基于自转年龄和锂丰度，Hercules-Lyra 星协的精炼年龄是多少？
• RQ2 Her-Lyr 中锂等效宽度的分布与昴星团及其他年轻星协相比如何？
• RQ3 Her-Lyr 星协的多重性频率及其伴星性质如何，特别是低质量恒星和棕矮星候选者？
• RQ4 Her-Lyr 星协是否在运动学和动力学上与 UMa、AB Dor 或 SACY 等其他本地移动星群相关联？
• RQ5 UV 空间中观测到的非成员分布的成因是什么？是否可能代表一个约 1 Gyr 的古老恒星流？

主要发现

• Hercules-Lyra 星协的自转年龄平均值约为 250 Myr。
• 观测到显著的锂等效宽度分布范围，与昴星团相当，且大于大熊座星群，表明其演化过程复杂或存在多次形成事件。
• Her-Lyr 的 X 射线光度函数与昴星团非常相似，支持其年轻且具有活跃的磁活动。
• 质量函数可精确约束至约 0.7 M☉，表明太阳邻近区域存在大量尚未被探测到的低质量恒星。
• UV 空间中的非成员可能对应一个约 1 Gyr 的古老恒星流，提示可能存在污染或动力学演化效应。
• 许多候选成员缺乏光谱或自转周期数据，凸显了后续观测的必要性，以进一步完善成员资格判定和恒星普查。