# Gas Flows Within Cavities of Circumbinary Discs in Eccentric Binary Protostellar Systems

## TL;DR

This study uses hydrodynamical simulations to analyze gas flow patterns within circumbinary disks around eccentric binary stars, revealing distinct flow structures that depend on orbital eccentricity and can inform observational diagnostics.

## Contribution

It provides new insights into how gas flows differ in eccentric versus circular binary systems, highlighting the importance of flow structures as indicators of orbital eccentricity.

## Key findings

- Gas fills the cavity more in highly eccentric systems.
- Eccentric binaries show tightly wound streams and figure-eight structures.
- Flow patterns can serve as diagnostics for binary orbital eccentricity.

## Abstract

The structure and evolution of gas flows within the cavity of a circumbinary disk (CBD) surrounding the stellar components in eccentric binaries are examined via two-dimensional hydrodynamical simulations. The degree to which gas fills the cavity between the circumstellar disks (CSDs) and the CBD is found to be greater for highly eccentric systems, in comparison to low-eccentricity systems, reflecting the spatial extent over which mass enters into the cavity throughout the orbit. The pattern of the gas flow in the cavity differs for eccentric binaries from that of binaries in a circular orbit. In particular, the former reveals tightly wound gas streams and figure-eight-like structures for systems characterized by eccentricities, $e \ge 0.4$, whereas the latter only reveal relatively loosely bent streams from the CBD to the CSDs. Hence, the description of the stream structures can be a probe of sufficient non-circularity of the binary orbital motion. Given that the inner edge of the CBD is not very well defined for highly eccentric systems due to the complex gas structures, it is suggested that the area of the cavity for high-sensitivity imaging observations may prove to be a more useful diagnostic for probing the effectiveness of CBD clearing in the future.