Hunting for planets in the HL Tau disk

TL;DR

This study used mid-infrared direct imaging to search for young planets in the HL Tau disk, setting upper mass limits and suggesting that observed gaps may be caused by less massive planets than detectable.

Contribution

First direct imaging constraints on young planets in HL Tau, providing upper mass limits and insights into gap formation mechanisms.

Findings

No planets detected at the gap locations.

Upper mass limits of 10-15 Jupiter masses for potential planets.

Gaps may be caused by less massive planets not detectable with current sensitivity.

Abstract

Recent ALMA images of HL Tau show gaps in the dusty disk that may be caused by planetary bodies. Given the young age of this system, if confirmed, this finding would imply very short timescales for planet formation, probably in a gravitationally unstable disk. To test this scenario, we searched for young planets by means of direct imaging in the L'-band using the Large Binocular Telescope Interferometer mid-infrared camera. At the location of two prominent dips in the dust distribution at ~70AU (~0.5") from the central star we reach a contrast level of ~7.5mag. We did not detect any point source at the location of the rings. Using evolutionary models we derive upper limits of ~10-15MJup at <=0.5-1Ma for the possible planets. With these sensitivity limits we should have been able to detect companions sufficiently massive to open full gaps in the disk. The structures detected at mm-wavelengths could be gaps in the distributions of large grains on the disk midplane, caused by planets not massive enough to fully open gaps. Future ALMA observations of the molecular gas density profile and kinematics as well as higher contrast infrared observations may be able to provide a definitive answer.