A Close-up View of the Young Circumbinary Disk HD 142527 (1704.00787v1)

Abstract: We present ALMA observations of the 0.88 millimeter dust continuum, 13CO, and C18O J=3-2 line emission of the circumbinary disk HD142527 at a spatial resolution of about 0.25". This system is characterized by a large central cavity of roughly 120 AU in radius, and asymmetric dust and gas emission. By comparing the observations with theoretical models, we find that the azimuthal variations in gas and dust density reach a contrast of 54 for dust grains and 3.75 for CO molecules, with an extreme gas-to-dust ratio of 1.7 on the dust crescent. We point out that caution is required in interpreting continuum subtracted maps of the line emission as this process might result in removing a large fraction of the line emission. Radially, we find that both the gas and dust surface densities can be described by Gaussians, centered at the same disk radius, and with gas profiles wider than for the dust. These results strongly support a scenario in which millimeter dust grains are radially and azimuthally trapped toward the center of a gas pressure bump. Finally, our observations reveal a compact source of continuum and CO emission inside the dust depleted cavity at about 50 AU from the primary star. The kinematics of the CO emission from this region is different from that expected from material in Keplerian rotation around the binary system, and might instead trace a compact disk around a third companion. Higher angular resolution observations are required to investigate the nature of this source.

A Close-Up View of the Young Circumbinary Disk HD 142527

The paper presented in this paper offers a detailed analysis of the circumbinary disk surrounding the HD 142527 system, utilizing observations from the Atacama Large Millimeter/submillimeter Array (ALMA). The disk is notable for its substantial central cavity and asymmetric dust and gas distributions, properties that are important to understanding planet formation processes and disk dynamics around binary systems.

Observational Analysis

The observations focus on the 0.88 millimeter dust continuum alongside $^{13}$CO and C$^{18}$O J=3-2 line emissions, achieving a spatial resolution of approximately 0.25 arcseconds. This resolution enables the exploration of intricate disk structures in substantial detail. The central cavity of the disk measures around 120 AU in radius, which is significant given that typical circumstellar disks around solitary stars exhibit much smaller cavities. Such large cavities are often attributed to the gravitational influence of massive companions like stellar or planetary bodies.

Results Summary

The analysis reveals a pronounced contrast in azimuthal variations of gas and dust density, with a disparity of 54 to 1 for dust grains and 3.75 to 1 for CO molecules. The recorded gas-to-dust ratio is particularly low at 1.7 in the dust crescent, indicating a strong dust trapping efficiency possibly due to pressure bumps in the gaseous environment. These observations underscore that millimeter-sized dust grains are subject to radial and azimuthal trapping, a process integral to the formation of larger planetary bodies.

Additionally, a compact source within the dust-depleted cavity at roughly 50 AU from the primary star was identified, exhibiting kinematics inconsistent with expected Keplerian rotation. This suggests the potential presence of a second disk around an otherwise undetected third companion, though more precise observations are necessary to confirm this hypothesis.

Implications for Disk and Planet Formation Models

The findings strongly support the model where pressure variations in the gas create conditions conducive to dust trapping. These regions of trapped dust can serve as sites for the gradual coalescence into larger planetary bodies, a cornerstone concept in current planet formation theories. The large cavity and asymmetric structures align with expectations from circumstellar dynamics influenced by binary companions, though the precise origin of such large cavities and asymmetries remains a complex puzzle. Potential explanations include gravitational interactions with known or unknown companions or intrinsic disk instabilities such as the Rossby-wave instability.

Future Directions and Theoretical Context

The disk around HD 142527 presents a valuable case paper for refining theoretical models of disk dynamics, particularly those involving complex interactions within binary systems. The discovered structures motivate further high-resolution studies to probe the interactions of circumbinary disks with potential planetary bodies. Such systems can offer crucial insights into how planetary formation processes are altered in binary settings relative to standard circumstellar disk scenarios.

For future work, refining models that simulate dust dynamics in such disks with consideration for varied particle sizes and compositions can illuminate the comprehensive dust trapping mechanics. Additionally, integrating observational data from other systems with similar features may provide a broader understanding of disk evolution constraints and planet formation variability.

This paper contributes significantly to the ongoing discourse on circumstellar disk physics, emphasizing the complexity of interactions that govern disk morphology and evolution in binary star systems.