Circumbinary Ring, Circumstellar disks and accretion in the binary system UY Aurigae

TL;DR

This study confirms the presence of a circumbinary disk in UY Aurigae, resolves circumstellar disks, and reveals complex gas dynamics indicating active accretion and possible multiplicity within the system.

Contribution

It provides detailed observational evidence of the UY Aurigae system's disk structures and gas kinematics, suggesting active accretion and potential multiplicity, which advances understanding of binary star evolution.

Findings

Confirmed existence of a circumbinary disk in UY Aurigae.

Resolved circumstellar disks at 1.4 mm with low spectral indices.

Detected complex gas motions including infall, outflow, and streaming accretion.

Abstract

Recent exo-planetary surveys reveal that planets can orbit and survive around binary stars. This suggests that some fraction of young binary systems which possess massive circumbinary disks (CB) may be in the midst of planet formation. However, there are very few CB disks detected. We revisit one of the known CB disks, the UY Aurigae system, and probe 13CO 2-1, C18O 2-1, SO 5(6)-4(5) and 12CO 3-2 line emission and the thermal dust continuum. Our new results confirm the existence of the CB disk. In addition, the circumstellar (CS) disks are clearly resolved in dust continuum at 1.4 mm. The spectral indices between the wavelengths of 0.85 mm and 6 cm are found to be surprisingly low, being 1.6 for both CS disks. The deprojected separation of the binary is 1.26" based on our 1.4 mm continuum data. This is 0.07" (10 AU) larger than in earlier studies. Combining the fact of the variation of UY Aur B in $R$ band, we propose that the CS disk of an undetected companion UY Aur Bb obscures UY Aur Ba. A very complex kinematical pattern inside the CB disk is observed due to a mixing of Keplerian rotation of the CB disk, the infall and outflow gas. The streaming gas accreting from the CB ring toward the CS disks and possible outflows are also identified and resolved. The SO emission is found to be at the bases of the streaming shocks. Our results suggest that the UY Aur system is undergoing an active accretion phase from the CB disk to the CS disks. The UY Aur B might also be a binary system, making the UY Aur a triple system.