Context. A complex environment exists in the inner few astronomical units of planet-forming disks. High-angular-resolution observations play a key role in our understanding of the disk structure... Show moreContext. A complex environment exists in the inner few astronomical units of planet-forming disks. High-angular-resolution observations play a key role in our understanding of the disk structure and the dynamical processes at work.Aims: In this study we aim to characterize the mid-infrared brightness distribution of the inner disk of the young intermediate-mass star HD 163296 from early VLTI/MATISSE observations taken in the L- and N-bands. We put special emphasis on the detection of potential disk asymmetries.Methods: We use simple geometric models to fit the interferometric visibilities and closure phases. Our models include a smoothed ring, a flat disk with an inner cavity, and a 2D Gaussian. The models can account for disk inclination and for azimuthal asymmetries as well. We also perform numerical hydrodynamical simulations of the inner edge of the disk.Results: Our modeling reveals a significant brightness asymmetry in the L-band disk emission. The brightness maximum of the asymmetry is located at the NW part of the disk image, nearly at the position angle of the semimajor axis. The surface brightness ratio in the azimuthal variation is 3.5 ± 0.2. Comparing our result on the location of the asymmetry with other interferometric measurements, we confirm that the morphology of the r < 0.3 au disk region is time-variable. We propose that this asymmetric structure, located in or near the inner rim of the dusty disk, orbits the star. To find the physical origin of the asymmetry, we tested a hypothesis where a vortex is created by Rossby wave instability, and we find that a unique large-scale vortex may be compatible with our data. The half-light radius of the L-band-emitting region is 0.33 ±0.01 au, the inclination is 52°(-7°/+5°), and the position angle is 143° ± 3°. Our models predict that a non-negligible fraction of the L-band disk emission originates inside the dust sublimation radius for μm-sized grains. Refractory grains or large (≳10 μm-sized) grains could be the origin of this emission. N-band observations may also support a lack of small silicate grains in the innermost disk (r ≲ 0.6 au), in agreement with our findings from L-band data. Show less
MATISSE, the VLTI 2nd generation spectro-interferometric L, M and N bands imager, has been commissioned from March 2018 to March 2020. It is open to the General User since April 2019. A complete... Show moreMATISSE, the VLTI 2nd generation spectro-interferometric L, M and N bands imager, has been commissioned from March 2018 to March 2020. It is open to the General User since April 2019. A complete analysis of its performances is given in this paper for MATISSE standalone (with UTs and ATs) and for the GRAVITY for MATISSE (GRA4MAT) mode (with ATs) where the GRAVITY fringe tracker is used to stabilize the fringes in MATISSE and hence improve its sensitivity and spectral coverage at high spectral resolution. This paper presents the key operation parameters of MATISSE and decomposes its performances in fundamental precision per spectral channel for all measurements and in broad band calibration errors on the accuracy of visibility and closure phase. It is intended to give the user a full description of the different errors that must be considered and weighted in the model fitting and image reconstruction. The first image reconstructions achieved by MATISSE are discussed. The performances demonstrated here in the full very broad spectral domain of MATISSE open a very large domain of scientific applications that includes but strongly expands quantitatively and qualitatively the initial science program of the first generation instrument MIDI and, combined with GRAVITY, offers an extremely powerful tool to characterize the temperature and composition of dusty and molecular components of YSOs, AGNs and evolved stars. Show less
