十个反中心疏散星团的丰度和运动学
Abundances and kinematics for ten anticentre open clusters
摘要：
疏散星团分布在整个磁盘上，是其属性的方便示踪剂。特别是，外盘星团承担的银河系盘的化学演化的调查的关键作用。本研究的目标是获得均匀的元素丰度的样本外盘OC十，并调查可能的联系与磁盘结构，如银河系的Anticenter恒星结构。我们分析了红巨星的高分辨率光谱，从HIRES@Keck和UVES@VLT档案中获得。用经典的等效宽度方法计算了元素丰度和恒星大气参数。我们还利用自行进行了轨道积分。我们得到的Fe丰度在盘的外部12 kpc处跟踪一个斜率为-0.027+/-0.007 dex.kpc-1的浅的负径向金属丰度梯度。[α/Fe]梯度显示为平坦，斜率为0.006+/-0.007 dex.kpc-1。最外层的两个星团（Be 29和Sau 1）似乎遵循椭圆轨道。Be 20也呈现出一个在平面上方有很大偏移的特殊轨道。三个最缺乏金属的星系团（其中两个位于银河系盘的边缘）的不规则轨道，如果得到更可靠的天体测量（如盖亚任务的测量）的证实，则与银河系由内而外形成的情况相一致，其中河外物质被吸积到外盘上。我们无法确定Be 20、Be 29和Sau 1是否来自河外星系，因为它们可能是古老的真正的银河系星团，其轨道在过去的5 Gyr中受到吸积事件或轻微合并的扰动，或者它们可能是厚盘人口的代表。这些物体的性质很有趣，值得在不久的将来进一步研究。
英文摘要：
Open clusters are distributed all across the disk and are convenient tracers of its properties. In particular, outer disk clusters bear a key role for the investigation of the chemical evolution of the Galactic disk. The goal of this study is to derive homogeneous elemental abundances for a sample of ten outer disk OCs, and investigate possible links with disk structures such as the Galactic Anticenter Stellar Structure. We analyse high-resolution spectra of red giants, obtained from the HIRES@Keck and UVES@VLT archives. We derive elemental abundances and stellar atmosphere parameters by means of the classical equivalent width method. We also performed orbit integrations using proper motions. The Fe abundances we derive trace a shallow negative radial metallicity gradient of slope -0.027+/-0.007 dex.kpc-1 in the outer 12 kpc of the disk. The [alpha/Fe] gradient appears flat, with a slope of 0.006+/-0.007 dex.kpc-1 . The two outermost clusters (Be 29 and Sau 1) appear to follow elliptical orbits. Be 20 also exhibits a peculiar orbit with a large excursion above the plane. The irregular orbits of the three most metal-poor clusters (of which two are located at the edge of the Galactic disk), if confirmed by more robust astrometric measurements such as those of the Gaia mission, are compatible with an inside-out formation scenario for the Milky Way, in which extragalactic material is accreted onto the outer disk. We cannot determine if Be 20, Be 29,and Sau 1 are of extragalactic origin, as they may be old genuine Galactic clusters whose orbits were perturbed by accretion events or minor mergers in the past 5 Gyr, or they may be representants of the thick disk population. The nature of these objects is intriguing and deserves further investigations in the near future.
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