The Early ALMA View of the FU Ori Outburst System

TL;DR

This study uses ALMA observations to analyze the FU Ori outburst system, revealing details about its binary components, disk masses, and molecular environment, which are crucial for understanding star formation during outburst events.

Contribution

First high-resolution ALMA observations of FU Ori system that resolve binary disks and molecular gas, providing new insights into their structure and environment.

Findings

Detected two unresolved binary components with well-modeled continuum emission.

Derived disk dust masses of 2e-4 and 8e-5 solar masses for the two components.

Found molecular emission indicating denser gas around the southern component.

Abstract

We have obtained ALMA Band 7 observations of the FU Ori outburst system at 0.6"x0.5" resolution to measure the link between the inner disk instability and the outer disk through sub-mm continuum and molecular line observations. Our observations detect continuum emission which can be well modeled by two unresolved sources located at the position of each binary component. The interferometric observations recover the entire flux reported in previous single-dish studies, ruling out the presence of a large envelope. Assuming that the dust is optically thin, we derive disk dust masses of $2\times 10^{-4}$M$_{\odot}$ and $8\times 10^{-5}$M$_{\odot}$, for the north and south components respectively. We place limits on the disks' radii of $r<$45 AU. We report the detection of molecular emission from $^{12}$CO(3-2), HCO$^{+}$(4-3) and from HCN(4-3). The $^{12}$CO appears widespread across the two binary components, and is slightly more extended than the continuum emission. The denser gas tracer HCO$^{+}$ peaks close to the position of the southern binary component, while HCN appears peaked at the position of the northern component. This suggests that the southern binary component is embedded in denser molecular material, consistent with previous studies that indicate a heavily reddened object. At this angular resolution any interaction between the two unresolved disk components cannot be disentangled. Higher resolution images are vital to understanding the process of star formation via rapid accretion FU Ori-type episodes.