The Atacama Large Millimeter/submillimeter Array (ALMA) has detected substructures in numerous protoplanetary disks at radii from a few to over 100 au. These substructures are commonly thought to be associated with planet formation, either by serving as sites fostering planetesimal formation or by arising as a consequence of planet–disk interactions. Our current understanding of substructures, though, is primarily based on observations of nearby star-forming regions with mild UV environments, whereas stars are typically born in much harsher UV environments, which may inhibit planet formation in the outer disk through external photoevaporation. We present high-resolution (∼8 au) ALMA 1.3 mm continuum images of eight disks in σ Orionis, a cluster irradiated by an O9.5 star. Gaps and rings are resolved in the images of five disks. The most striking of these is SO 1274, which features five gaps that appear to be arranged nearly in a resonant chain. In addition, we infer the presence of gap or shoulder-like structures in the other three disks through visibility modeling. These observations indicate that substructures robustly form and survive at semimajor axes of several tens of au or less in disks exposed to intermediate levels of external UV radiation as well as in compact disks. However, our observations also suggest that disks in σ Orionis are mostly small, and thus millimeter continuum gaps beyond a disk radius of 50 au are rare in this region, possibly due to either external photoevaporation or age effects.

中文翻译：

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猎户座 σ 中结构丰富的原行星盘的高分辨率 ALMA 观测


阿塔卡马大型毫米/亚毫米阵列 （ALMA） 已经在半径从几到超过 100 天文单位的众多原行星盘中检测到了子结构。这些子结构通常被认为与行星形成有关，要么是作为促进行星形成的场所，要么是行星与盘相互作用的结果。不过，我们目前对子结构的理解主要基于对附近恒星形成区域的观察和温和的紫外线环境，而恒星通常诞生于更恶劣的紫外线环境中，这可能会通过外部光蒸发抑制行星在外盘中的形成。我们展示了猎户座σ座（一个由 O9.5 星照射的星团）中八个圆盘的高分辨率 （∼8 au） ALMA 1.3 毫米连续图像。间隙和环在 5 个磁盘的映像中解析。其中最引人注目的是 SO 1274，它有五个间隙，似乎几乎排列成一个共振链。此外，我们通过可见性建模推断其他三个圆盘中存在间隙或肩状结构。这些观察结果表明，在暴露于中等水平外部紫外线辐射的圆盘以及紧凑型圆盘中，子结构在几十 au 或更小的半长轴上稳健地形成和存活。然而，我们的观察还表明，猎户座σ盘大多很小，因此超过 50 au 的盘半径的毫米连续间隙在该区域很少见，这可能是由于外部光蒸发或年龄效应。