Speaker
Description
Although massive stars ( >8M_sun) are rare, they play a key role in the chemical and dynamical evolution of galaxies through their radiation, stellar winds, and supernova explosions. However, the physical mechanisms that govern their formation remain poorly understood. Unlike low-mass stars, whose growth is well described by the magnetospheric accretion scenario by which material is channeled along magnetic field lines onto the stellar surface, massive young stellar objects (MYSOs) cannot sustain this sun process because their magnetic fields are weak or even absent. In addition, observational studies of MYSOs are particularly challenging, as they remain deeply embedded in their natal envelopes during most of their early evolution. These facts have prevented direct measurements of mass accretion rates in the high-mass regime. In this talk I will describe my current work on a sample of MYSOS that, for reasons not yet understood, are observable at optical wavelengths. Their spectra show clear signatures of ongoing accretion, such as continuum excess and numerous emission lines. Using these diagnostics, we are deriving mass accretion rates within a non-magnetic accretion framework. Furthermore, we will establish empirical relations between the accretion and emission line luminosities that will allow the community to easily infer mass accretion rates of wide samples of MYSOs. Our results will provide the first solid constraints on the accretion of massive stars.
