  Protoplanetary disks drive some of the formation process (e.g., accretion,
gas dissipation, formation of structures, etc.) of stars and planets.
Understanding such physical processes is one of the main astrophysical
questions. HD 163296 is an interesting young stellar object for which infrared
and sub-millimeter observations have shown a prominent circumstellar disk with
gaps plausibly created by forming planets. This study aims at characterizing
the morphology of the inner disk in HD 163296 with multi-epoch near-infrared
interferometric observations performed with GRAVITY at the Very Large Telescope
Interferometer (VLTI). Our goal is to depict the K-band (lambda_0 ~ 2.2 um)
structure of the inner rim with milliarcsecond (sub-au) angular resolution. Our
data is complemented with archival PIONIER (H-band; lambda_0 ~ 1.65 um) data of
the source. We performed a Gradient Descent parametric model fitting to recover
the sub-au morphology of our source. Our analysis shows the existence of an
asymmetry in the disk surrounding the central star of HD 163296. We confirm
variability of the disk structure in the inner ~2 mas (0.2 au). While
variability of the inner disk structure in this source has been suggested by
previous interferometric studies, this is the first time that it is confirmed
in the H- and K-bands by using a complete analysis of the closure phases and
squared visibilities over several epochs. Because of the separation from the
star, position changes, and persistence of this asymmetric structure on
timescales of several years, we argue that it is a dusty feature (e.g., a
vortex or dust clouds), probably, made by a mixing of sillicate and carbon dust
and/or refractory grains, inhomogeneously distributed above the mid-plane of
the disk.
