Massive young stellar object (MYSOs) form during the collapse of high-mass pre-stellar cores, where infalling molecular material is accreted through a centrifugally-balanced accretion disc that is subject to efficient gravitational instabilities. In the resulting fragmented accretion disc of the MYSO, gaseous clumps and low-mass stellar companions can form, which will influence the future evolution of massive protostars in the Hertzsprung-Russell diagram. We perform dust continuum radiative transfer calculations and compute synthetic images of disc structures modelled by the gravito-radiation-hydrodynamics simulation of a forming MYSO, in order to investigate the Atacama Large Millimeter/submillimeter Array (ALMA) observability of circumstellar gaseous clumps and forming multiple systems. Both spiral arms and gaseous clumps located at ~a few 100 au from the protostar can be resolved by interferometric ALMA Cycle 7 C43-8 and C43-10 observations at band 6 (1.2 mm), using a maximal 0.015" beam angular resolution and at least 10-30 min exposure time for sources at distances of 1-2 kpc. Our study shows that substructures are observable regardless of their viewing geometry or can be inferred in the case of an edge-viewed disc. The observation probability of the clumps increases with the gradually increasing efficiency of gravitational instability at work as the disc evolves. As a consequence, large discs around MYSOs close to the zero-age-main-sequence line exhibit more substructures than at the end of the gravitational collapse. Our results motivate further observational campaigns devoted to the close surroundings of the massive protostars S255IR-NIRS3 and NGC 6334I-MM1, whose recent outbursts are a probable signature of disc fragmentation and accretion variability.
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Perseus Protostars. VI. Characterizing the Formation Mechanism for Close Multiple Systems
The VLA/ALMA Nascent Disk and Multiplicity (VANDAM) Survey of Orion Protostars I. Identifying and Characterizing the Protostellar Content of the OMC2-FIR4 and OMC2-FIR3 Regions
Nascent Embedded-protostar Survey in Taurus (NEST) I: Protostellar Multiplicity
National Radio Astronomy Observatory（国家射电天文台）；University of Virginia（弗吉尼亚大学）；Space Science Institute（太空科学研究所）；University of Wisconsin-Madison（威斯康星大学麦迪逊分校）；SKA Observatory（平方公里阵列望远镜观测站）；University of Arizona（亚利桑那大学）
ALMA images of discs: are all gaps carved by planets?
原行星盘现在经常被观察到，而系外行星在无数次间接发现之后，开始直接成像。为了更好地理解行星形成的过程，下一步是探测正在形成的行星或仍在其盘中的年轻行星的路标，例如间隙。一个壮观的例子是HL Tau的ALMA科学验证图像，显示其圆盘中有许多缺口和环。为了研究行星间隙的可观测性，我们对含有5兆焦耳间隙开放行星的气体和尘埃盘进行了3D流体动力学模拟，并描述了迁移，生长和破碎尘埃颗粒的空间分布。然后，我们为ALMA计算相应的合成图像。对于15 m s-1的碰撞速度的尘埃碎片化阈值的值，我们确定的第一次自我诱导的尘埃堆在模拟考虑到碎片。这个特征，除了容易检测到的行星间隙之外，还导致了第二个明显的间隙，可能被误认为是第二颗行星的特征。因此，在解释间隙检测时必须谨慎。
