Accretion signatures in massive young stellar objects

Abstract

I review recent observational progress on the search for accretion signatures in massive young stellar objects (MYSOs). In this context, the primary tool will be 1–5 μm high resolution ($\lambda/\Delta\lambda \,{=}\,$50,000) spectroscopy. The observational regime is the phase between massive star formation (collapse, accretion, mergers, etc) and the fully revealed OB star photosphere, the phase for which the term “Massive Star Birth” was originally coined. In this phase, we seek both the signature of the earlier accretion process and the photospheric markers of the truly massive star which is on the main sequence. The sample of objects used in this endeavor are massive young stars located in nascent clusters powering Galactic giant H II regions. Emission in the 2.3 μm 2–0 vibrational–rotational bandhead of CO is observed as are the ionized lines of Hydrogen, Helium, and other abundant elements. High spectral resolution is key in giving geometrical clues to the circumstellar emission sources, both through individual line profiles (i.e. shapes) and positions.