分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Up to date, only 13 firmly established triple microlensing events have been discovered, so the occurrence rates of microlensing two-planet systems and planets in binary systems are still uncertain. With the upcoming space-based microlensing surveys, hundreds of triple microlensing events will be detected. To provide clues for future observations and statistical analyses, we initiate a project to investigate the detectability of triple-lens systems with different configurations and observational setups. As the first step, in this work we develop the simulation software and investigate the detectability of a scaled Sun-Jupiter-Saturn system with the recently proposed telescope for microlensing observation on the ``Earth 2.0 (ET)'' satellite. With the same $\Delta\chi^2$ thresholds of detecting a single planet and two planets, we find that the detectability of the scaled Sun-Jupiter-Saturn analog is about 1% and the presence of the Jovian planet suppresses the detectability of the Saturn-like planet by $\sim $13% regardless of the adopted detection $\Delta\chi^2$ threshold. This suppression probability could be at the same level as the Poisson noise of future space-based statistical samples of triple-lenses, so it is inappropriate to treat each planet separately during detection efficiency calculations.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Recent ALMA observations have revealed that a large fraction of protoplanetary discs contain bright rings at (sub)millimeter wavelengths. Dust trapping induced by pressure maxima in the gas disc is a popular explanation for these rings. However, it is unclear whether such pressure bumps can survive for evolutionary time-scales of the disc. In this work, we investigate an alternative scenario, which involves only dust-gas interactions in a smooth gas disc. We postulate that ALMA rings are a manifestation of a dense, clumpy mid-plane that is actively forming planetesimals. The clumpy medium itself hardly experiences radial drift, but clumps lose mass by disintegration and vertical transport and planetesimal formation. Starting from a seed ring, we numerically solve the transport equations to investigate the ring's survival. In general, rings move outward, due to diffusion of the clump component. Without pressure support, rings leak material at rates $\sim$40 $M_\oplus\,\mathrm{Myr}^{-1}$ and in order for rings to survive, they must feed from an external mass reservoir of pebbles. In the case where the pebble size is constant in the disk, a cycle between ring formation and dispersion emerges. Rings produce large quantities of planetesimals, which could be material for planet formation and explain the massive budget inferred debris disc. Mock images of ALMA observations compare well to the rings of Elias 24 and AS 209 from DSHARP's sample.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the past decade, ALMA observations have revealed that a large fraction of protoplanetary discs contains rings in the dust continuum. These rings are the locations where pebbles accumulate, which is beneficial for planetesimal formation and subsequent planet assembly. We investigate the viability of planet formation inside ALMA rings in which pebbles are trapped by either a Gaussian-shape pressure bump or by the strong dust backreaction. Planetesimals form at the midplane of the ring via streaming instability. By conducting N-body simulations, we study the growth of these planetesimals by collisional mergers and pebble accretion. Thanks to the high concentration of pebbles in the ring, the growth of planetesimals by pebble accretion becomes efficient as soon as they are born. We find that planet migration plays a decisive role in the evolution of rings and planets. For discs where planets can migrate inward from the ring, a steady state is reached where the ring spawns ${\sim}20 M_\oplus$ planetary cores as long as rings are fed with materials from the outer disc. The ring acts as a long-lived planet factory and it can explain the 'fine-tuned' optical depths of the observed dust rings in the DSHARP large program. In contrast, in the absence of a planet removal mechanism (migration), a single massive planet will form and destroy the ring. A wide and massive planetesimals belt will be left at the location of the planet-forming ring. Planet formation in rings may explain the mature planetary systems observed inside debris discs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： In the past decade, ALMA observations have revealed that a large fraction of protoplanetary discs contains rings in the dust continuum. These rings are the locations where pebbles accumulate, which is beneficial for planetesimal formation and subsequent planet assembly. We investigate the viability of planet formation inside ALMA rings in which pebbles are trapped by either a Gaussian-shape pressure bump or by the strong dust backreaction. Planetesimals form at the midplane of the ring via streaming instability. By conducting N-body simulations, we study the growth of these planetesimals by collisional mergers and pebble accretion. Thanks to the high concentration of pebbles in the ring, the growth of planetesimals by pebble accretion becomes efficient as soon as they are born. We find that planet migration plays a decisive role in the evolution of rings and planets. For discs where planets can migrate inward from the ring, a steady state is reached where the ring spawns ${\sim}20 M_\oplus$ planetary cores as long as rings are fed with materials from the outer disc. The ring acts as a long-lived planet factory and it can explain the 'fine-tuned' optical depths of the observed dust rings in the DSHARP large program. In contrast, in the absence of a planet removal mechanism (migration), a single massive planet will form and destroy the ring. A wide and massive planetesimals belt will be left at the location of the planet-forming ring. Planet formation in rings may explain the mature planetary systems observed inside debris discs.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Recently, the Molecules with ALMA at Planet-forming Scales (MAPS) ALMA Large Program reported a high number of line emission substructures coincident with dust rings and gaps in the continuum emission, suggesting a causal link between these axisymmetric line emission and dust continuum substructures. To test the robustness of the claimed correlation, we compare the observed spatial overlap fraction in substructures with that from the null hypothesis, in which the overlap is assumed to arise from the random placement of line emission substructures. Our results reveal that there is no statistically significant evidence for a universal correlation between line emission and continuum substructures, questioning the frequently-made link between continuum rings and pressure bumps. The analysis also clearly identifies outliers. The chemical rings and the dust gaps in MWC 480 appear to be strongly correlated (${>}4\sigma$), and the gaps in the CO isotopologues tend to moderately (${\sim}3\sigma$) correlate with dust rings.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
摘要： Up to date, only 13 firmly established triple microlensing events have been discovered, so the occurrence rates of microlensing two-planet systems and planets in binary systems are still uncertain. With the upcoming space-based microlensing surveys, hundreds of triple microlensing events will be detected. To provide clues for future observations and statistical analyses, we initiate a project to investigate the detectability of triple-lens systems with different configurations and observational setups. As the first step, in this work we develop the simulation software and investigate the detectability of a scaled Sun-Jupiter-Saturn system with the recently proposed telescope for microlensing observation on the ``Earth 2.0 (ET)'' satellite. With the same $\Delta\chi^2$ thresholds of detecting a single planet and two planets, we find that the detectability of the scaled Sun-Jupiter-Saturn analog is about 1% and the presence of the Jovian planet suppresses the detectability of the Saturn-like planet by $\sim $13% regardless of the adopted detection $\Delta\chi^2$ threshold. This suppression probability could be at the same level as the Poisson noise of future space-based statistical samples of triple-lenses, so it is inappropriate to treat each planet separately during detection efficiency calculations.
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