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.
Highlights
Planetary systems form inside discs of gas and dust around pre-main sequence stars, within typical disc lifetimes of a few million years (e.g. Hernandez et al 2007; Fedele et al 2010)
We projected each frame onto 18 principal components (PCs) to build a model of the stellar speckle pattern over an annular region 0. 24-1.5
As an additional test to confirm the physical nature of the ‘b’ point-like source, we show in Appendix A its detection in a set of post-processed frames obtained running Principal Component Analysis (PCA)-angular differential imaging (ADI) with different parameters
Summary
Planetary systems form inside discs of gas and dust around pre-main sequence stars, within typical disc lifetimes of a few million years (e.g. Hernandez et al 2007; Fedele et al 2010). Direct imaging of exoplanets is a powerful technique that allows full spectroscopic, photometric and astrometric characterization of the planetary companions, and provides access to a wider range of planet-star separations (≥ 5 au) compared to other methods (see the review by Fischer et al 2014). The number of imaged exoplanets has been growing in the last few years, with several companions found in young systems (e.g. Lagrange et al 2010; Marois et al 2010; Rameau et al 2013; Macintosh et al 2015; Chauvin et al 2017)
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