Looking close at FU Orionis' disk in the mid-infrared with MATISSE/VLTI

FU Orionis is the archetype of a class of YSOs (FUors) that have experienced eruptive events due to increased mass accretion (as high as \(10^{-4}\) Msun/yr) flowing from the circumstellar disk onto the protostar. The inner accretion disk is subsequently heated by these eruptions, leading to short-period brightenings (ΔB~6 mag in FU Ori within one year) with long-term fading rates.  The FUors group consists currently of more than 20 stars, while it is yet unclear whether they constitute a typical step in early stellar evolution. FUors are ideal laboratories in studying the evolution of disks within a few years after an eruptive event. As the archetype, FU Orionis's disk is a well-studied object. Recently, near-infrared scattered light images (Laws et al. 2020) suggest that the size of the disk is \(\leq0.3\)", or else its radius is about 60 au at the adopted Gaia EDR3 distance (402.3 pc). Moreover, those images revealed a spiral-like arc, while previous ALMA sub-mm observations (Perez et al. 2020) tentatively suggested a link between a rotating disk and the arc feature. Motivated by these results, we opted to look at disk structures in L and N bands with MATISSE, the new mid-infrared, imaging instrument of the VLTI.