Probing the multiplicity of young massive stars with NIR interferometry and high-resolution imaging techniques

Most main sequence massive stars (~70%) belong to short-period binaries, a fact that does not reflect the binary parameters measured among populations of newly born massive stars. To bridge the gap between these two regimes, we need to obtain strong constrains on the origin of the pairing mechanism and the birth orbital properties. Different scenarios have been proposed to produce close binaries, such as the migration that can occur in the framework of disk fragmentation, in which massive binaries are originally formed at large separations and then harden on a time-scale of ~2 Myr. Testing this scenario requires to detect a significant number of relatively massive companions at separations corresponding to the expected size of the accretion disk. 

In my talk, I will describe how optical interferometry (GRAVITY) and high-angular resolution techniques (NACO) are of great importance in characterizing multiplicity at birth, on two different datasets. From the interferometric model fitting of the visibility amplitudes and closure phases, I will present some of my latest exciting results, including two important concepts: the multiplicity and companion fraction. In M17, we find a multiplicity fraction of 100% with 2.3 companions orbiting the central stars on average. Similarly, I will show a handful of preliminary multiplicity results from high-angular resolution images taken with NACO. These results will be compared to other recent studies and I will discuss the connection with the current star formation theories.