Planet formation in intermediate-separation binary systems

TL;DR

This study characterizes millimetre-wavelength discs in intermediate-separation binary systems, revealing asymmetries, dust mass differences, and low gas content, suggesting binarity influences disc evolution and planet formation potential.

Contribution

First detailed millimetre observations of individual discs in intermediate-separation binaries, highlighting asymmetries and low gas masses, and proposing binarity impacts disc evolution.

Findings

Discs detected in continuum but not in CO lines.

Primary discs have about three times more dust than secondaries.

Gas masses are below 0.1 Jupiter masses, limiting giant planet formation.

Abstract

We report the first characterisation of the individual discs in the intermediate separation binary systems KK Oph and HD 144668 at millimetre wavelengths. In both systems the circum-primary and the circum-secondary discs are detected in the millimetre continuum emission, but not in $^{13}$CO nor C$^{18}$O lines. Even though the disc structure is only marginally resolved, we find indications of large-scale asymmetries in the outer regions of the primary discs, most likely due to perturbation by the companion. The derived dust masses are firmly above debris disc level for all stars. The primaries have about three times more dust in their discs than the secondaries. In the case of HD 144668 the opacity spectral index of the primary and secondary differ by the large margin of 0.69 which may be a consequence of the secondary disc being more compact. Upper limits on the gas masses imply less than 0.1 M$_{\textrm{jup}}$ in any of these discs, meaning that giant planets can no longer form in them. Considering that there have been no massive gas discs identified to date in intermediate separation binaries (i.e., binaries at a few hundred au separation), this opens space for speculation whether their binarity causes the removal of gas, with tidal interaction truncating the discs and hence shortening the accretion timescale. More systematic studies in this respect are sorely needed.