BIMODIAL DISTRIBUTION OF GALACTIC DISK STARS ON THE [α/Fe]–[Fe/H] PLANE AS POSSIBLE EVIDENCE OF DISCONTINUOUS RADIAL MIGRATION HISTORY
BIMODIAL DISTRIBUTION OF GALACTIC DISK STARS ON THE [α/Fe]–[Fe/H] PLANE AS POSSIBLE EVIDENCE OF DISCONTINUOUS RADIAL MIGRATION HISTORY
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银盘恒星在[α/Fe]-[Fe/H]平面上的双峰分布作为不连续径向迁移历史的可能证据
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发表时间：
2016
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通讯作者：
M. Chiba
中科院分区：
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作者：
Daisuke Toyouchi;M. Chiba
我们研究了恒星的径向迁移历史在盘状星系化学演化中的作用，特别是在了解它们在[α/Fe] - [Fe/H]平面上双峰分布的起源。为此，我们研究了三种不同的模型，包括无、连续和不连续径向迁移（DRM）。我们发现，在有径向迁移的模型中，外盘区域恒星的[α/Fe]比值随时间下降的速度比没有径向迁移的模型更快，这是因为与之相关的中间和年老盘星从内盘区域向外盘区域的净转移增加了Ia型恒星相对于SNe II型恒星在后盘区域的速率。此外，在假设快速和DRM的模型中，它对大半径恒星丰度的影响是显著的，足以提供内外盘区域之间[α/Fe] - [Fe/H]平面上恒星演化的巨大差异。因此，我们得到了在银河系恒星盘观测到的[α/Fe] - [Fe/H]平面上的盘状恒星的双峰分布，从而暗示DRM事件可能在再现这张丰度比图上观测到的恒星双峰分布中起了关键作用。我们讨论了在银河系盘的早期演化中引起这种DRM的可能机制，包括一个相对较大的卫星与恒星盘的轻微合并事件。
We investigate the role of radial migration history of stars in chemical evolution of a disk galaxy, in particular in understanding the origin of their bimodal distribution on the [α/Fe]–[Fe/H] plane. For this purpose, we examine three different models with no, continuous, and discontinuous radial migration (DRM). We find that for the model with radial migration, the [α/Fe] ratios of stars in outer disk regions decrease more rapidly with time than the model without radial migration, because the associated net transfer of intermediate and old disk stars from inner to outer disk regions increases the rate of Type Ia relative to that of SNe II in the latter regions. Moreover, in the model assuming rapid and DRM, its effect on the stellar abundances at larger radii is significant enough to provide the large difference in the evolution of stars on the [α/Fe]–[Fe/H] plane between inner and outer disk regions. As a result, we obtain the bimodal distribution of disk stars on the [α/Fe]–[Fe/H] plane as observed in the Galactic stellar disk, thereby implying that the event of DRM may play a key role in reproducing the observed bimodality of stars on this abundance-ratio diagram. We discuss possible mechanisms causing such DRM in the early evolution of the Galactic disk, including the event of minor merging of a relatively massive satellite onto the stellar disk.