The potential of combining MATISSE and ALMA observations: constraining the structure of the innermost region in protoplanetary discs

Abstract

Context. In order to study the initial conditions of planet formation, it is crucial to obtain spatially resolved multi-wavelength observations of the innermost region of protoplanetary discs. Aims. We evaluate the advantage of combining observations with MATISSE/VLTI and ALMA to constrain the radial and vertical structure of the dust in the innermost region of circumstellar discs in nearby star-forming regions. Methods. Based on a disc model with a parameterized dust density distribution, we apply 3D radiative-transfer simulations to obtain ideal intensity maps. These are used to derive the corresponding wavelength-dependent visibilities we would obtain with MATISSE as well as ALMA maps simulated with CASA. Results. Within the considered parameter space, we find that constraining the dust density structure in the innermost 5 au around the central star is challenging with MATISSE alone, whereas ALMA observations with reasonable integration times allow us to derive significant constraints on the disc surface density. However, we find that the estimation of the different disc parameters can be considerably improved by combining MATISSE and ALMA observations. For example, combining a 30-minute ALMA observation (at 310 GHz with an angular resolution of 0.03 ) for MATISSE observations in the L and M bands (with visibility accuracies of about 3 %) allows the radial density slope and the dust surface density profile to be constrained to within ∆α = 0.3 and ∆(α − β) = 0.15, respectively. For an accuracy of ∼ 1 % even the disc flaring can be constrained to within ∆β = 0.1. To constrain the scale height to within 5 au, M band accuracies of 0.8 % are required. While ALMA is sensitive to the number of large dust grains settled to the disc midplane we find that the impact of the surface density distribution of the large grains on the observed quantities is small.

K-band GRAVITY/VLTI interferometry of “extreme” Herbig Be stars

“…On the contrary, stars with IR excesses starting at wavelengths longer than those corresponding to the K-band are expected to have r in values significantly larger than the sources that show nIR excess and are interferometrically resolved at these wavelengths. As a consequence, a robust analysis of the sizeluminosity relation should combine continuum interferometry at the K-band and at longer wavelengths (e.g., with MIDI and MA-TISSE at VLTI, Menu et al 2015;Kobus et al 2019) of a more complete sample of HAeBes belonging to both Group JH and Group K. Such an analysis is likely to add many more HBes with L * > 10 3 L ⊙ and large r in values. Thus, the apparent trend currently showing undersized HBes is most probably affected by the fact that the current sample includes a comparatively large number of such sources that have an excess starting at short, nIR wavelengths.…”