A VLTI view of Massive Young Stellar Objects (MYSOs)

The formation of massive stars, objects with masses larger than 8 times solar, is central to both stellar astronomy and galactic evolution. In recent years, significant progress has been made in understanding the formation of high-mass young stellar objects (MYSOs; i.e. M_∗ ≥ 8 M_⊙, L_bol ≥ 5 x 10³ L_⊙. The latest observational and theoretical studies present evidence that HMYSOs are born in the same way as their low-mass counterparts, via disc accretion, rather than through coalescence of lower mass stars (Rosen+ 2019; Klassen+ 2016; Kraus+ 2010). While the existence of massive protostellar discs has now been established, little is known about how they eventually disperse, and how this is linked to the central protostar. A recent interferometric study at mid-infrared wavelengths (VLTI/MIDI) has shown substructures in the discs of 8 HMYSOs and one source showed a spiral-gap structure (Frost et al. 2021). These substructures could be the result of a forming companion, thus understanding their formation is of great importance since massive stars have a high binary fraction. Moreover, investigating their inner structure, where the mass transfer to the protostar takes place, gives us insights in determining the physical and dynamical characteristics, as well as the accretion/ejection processes in HMYSOs. In this talk, I will present our results on a sample of MYSOs using VLTI/GRAVITY (operating in K-band) and discuss about the continuum and the gas (Brγ, Na I and CO lines) of their inner disc a few au from the star.