The asymmetric inner disk of the Herbig Ae star HD 163296 in the eyes of VLTI/MATISSE: evidence for a vortex?

Abstract

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 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.

Molecules with ALMA at Planet-forming Scales (MAPS). I. Program Overview and Highlights

“…HD 162396 has also been observed, though not detected, in high-J CO lines with Herschel (Du et al 2017), which together with continuum data, and [O I] and low-J CO line detections have provided constraints on the disk temperature structure and atmospheric gas to dust ratio (Tilling et al 2012). The inner disk also appears asymmetric, potentially hosting a large-scale vortex, which may impact its chemistry (Varga et al 2021).…”

A Gap at 1 au in the Disk of DI Cha A Revealed by Infrared Interferometry*

“…Menu et al (2015) and Varga et al (2018) analyzed the archival Very Large Telescope Interferometer (VLTI) MID-infrared Interferometric instrument (MIDI) observations for a large sample of T Tauri and Herbig Ae/Be stars, and suggested the existence of a disk population exhibiting astronomical-unit-scale cavities or gaps. New data obtained with the second generation interferometer VLTI/ MATISSE are confirming the complex inner structure of protoplanetary disks, including even the azimuthal asymmetric structures, like vortices (e.g., Varga et al 2020).…”

Commissioning MATISSE: operation and performances

“…Within the K band limits in table (7) GRA4MAT allows long exposures in L&M that enable reading the full detector and hence accessing simultaneously the full MATISSE spectral coverage as illustrated in figure (8). That figure displays one 10 s frame on the Be binary star δ Cen, which shows the very rich information that can be extracted from a single shot broad band observation at medium or high spectral resolution.…”

“…Observations in open time started in April 2019. The first science results have just been published [6,7] and many others are in the final steps of redaction. The commissioning of MATISSE has started in March 2018 and was scheduled to be concluded in May 2020.…”