On the age of the β Pictoris moving group
On the age of the β Pictoris moving group
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DOI：
10.1093/mnras/stu1894
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发表时间：
2014-09
影响因子：
4.8
通讯作者：
E. Mamajek;C. Bell
中科院分区：
文献类型：
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作者：
E. Mamajek;C. Bell
Jeffries & Binks（2014）和Malo et al.（2014）最近报道了风景如画的移动群（BPMG）的Li耗尽边界（LDB）年龄，它是经常引用的运动学年龄1200万年的两倍。在这项研究中，我们提出了（1）一个新的内部运动学的依巴谷天体测量和最好的公开发表的径向速度的评估，并评估是否可以推导出一个有用的运动学年龄，（2）推导等时线年龄的基础上的位置的A-，F-和G-型恒星的颜色星等图（CMD）。我们探讨的运动学的BPMG看速度的趋势沿着银河系轴，并进行回溯分析假设线性轨迹，周转轨道近似，并使用一个现实的引力势的轨道整合。使用现代速度数据，没有一种方法产生具有小不确定性的运动学年龄。银河系X和Y方向的膨胀仅在1.7 σ和2.7 σ水平上才有意义，它们共同产生了一个范围很广的整体运动学年龄（1300万~ 5800万年; 95% CL）。A型成员都位于零年龄主序上，表明年龄为2000万年，晚期F型和G型前主序BPMG成员的CMD位置的基因座的等时年龄中位数为2200万年（300万年统计，$\pm $100万系统）当考虑四套现代理论等时线时。最近LDB和等时年龄分析的结果与BPMG年龄中位数23 $\pm $3 Myr（总体1{\sigma}不确定性，包括$\pm $2 Myr统计和$\pm $2 Myr系统不确定性）一致。
Jeffries & Binks (2014) and Malo et al. (2014) have recently reported Li depletion boundary (LDB) ages for the {\beta} Pictoris moving group (BPMG) which are twice as old as the oft-cited kinematic age of $\sim$12 Myr. In this study we present (1) a new evaluation of the internal kinematics of the BPMG using the revised Hipparcos astrometry and best available published radial velocities, and assess whether a useful kinematic age can be derived, and (2) derive an isochronal age based on the placement of the A-, F- and G-type stars in the colour-magnitude diagram (CMD). We explore the kinematics of the BPMG looking at velocity trends along Galactic axes, and conducting traceback analyses assuming linear trajectories, epicyclic orbit approximation, and orbit integration using a realistic gravitational potential. None of the methodologies yield a kinematic age with small uncertainties using modern velocity data. Expansion in the Galactic X and Y directions is significant only at the 1.7{\sigma} and 2.7{\sigma} levels, and together yields an overall kinematic age with a wide range (13-58 Myr; 95 per cent CL). The A-type members are all on the zero age-main-sequence, suggestive of an age of $>$20Myr, and the loci of the CMD positions for the late-F- and G-type pre-main-sequence BPMG members have a median isochronal age of 22 Myr ($\pm$ 3 Myr stat., $\pm$ 1 Myr sys.) when considering four sets of modern theoretical isochrones. The results from recent LDB and isochronal age analyses are now in agreement with a median BPMG age of 23 $\pm$ 3 Myr (overall 1{\sigma} uncertainty, including $\pm$2 Myr statistical and $\pm$2 Myr systematic uncertainties).