High-contrast imaging of HD 163296 with the Keck/NIRC2 L'-band vortex coronograph

TL;DR

This study used Keck/NIRC2 L'-band vortex coronagraphy to image the HD 163296 disc, detecting a potential protoplanet and setting upper limits on planet masses at various gaps, advancing understanding of planet formation.

Contribution

First high-contrast L'-band imaging of HD 163296 revealing a candidate protoplanet and constraining planet masses at disc gaps.

Findings

Detected a point-like source near the second gap, possibly a 6-7 M_J protoplanet.

Set upper mass limits of 8-15 M_J, 4.5-6.5 M_J, and 2.5-4.0 M_J at the first, second, and third gaps.

Observed an arc-like scattered light feature associated with the first bright ring.

Abstract

We present observations of the nearby (D$\sim$100\,pc) Herbig star HD~163296 taken with the vortex coronograph at Keck/NIRC2 in the L' band (3.7~$\mu$m), to search for planetary mass companions in the ringed disc surrounding this pre-main sequence star. The images reveal an arc-like region of scattered light from the disc surface layers that is likely associated with the first bright ring detected with ALMA in the $\lambda$=1.3mm dust continuum at $\sim$65~au. We also detect a point-like source at $\sim$0\farcs5 projected separation in the North-East direction, close to the inner edge of the second gap in the millimetre images. Comparing the point source photometry with the atmospheric emission models of non-accreting giant planets, we obtain a mass of 6--7~M$_J$ for a putative protoplanet, assuming a system age of 5~Myr. Based on the contrast at a 95\% level of completeness calculated on the emission-free regions of our images, we set upper limits for the masses of giant planets of 8--15~M$_J$, 4.5--6.5~M$_J$ and 2.5-4.0~M$_J$ at the locations of the first, second and third gap in the millimetre dust continuum, respectively. Further deep, high resolution thermal IR imaging of the HD~163296 system are warranted, to confirm the presence and nature of the point source and to better understand the structure of the dust disc.