EPoS Contribution
EPoS Contribution
Massive pre-main sequence stars in M17

Maria-Claudia Ramirez-Tannus
API, Amsterdam, NL
The formation process of massive stars is poorly understood, mainly due to the lack of observations covering the early phases in the life of massive stars. Formation timescales are expected to be short; therefore, massive young stellar objects (mYSOs) are deeply embedded in their parental clouds. M17 is one of the most prominent HII regions in the sky, is relatively nearby d = 1.9 pc, and hosts a young massive star population. With X-shooter on the ESO Very Large Telescope we have obtained optical to near-infrared spectra of half a dozen mYSOs. The high-quality spectra enable a detailed spectroscopic analysis of the photospheres and circumstellar disks of these mYSOs. We confirm that these mYSOs are bloated, young massive stars contracting towards the main sequence, still surrounded by a (remnant?) accretion disk. We compare the observed properties with evolutionary tracks of massive protostars, and demonstrate that these mYSOs near the western edge of the HII region are on their way to become OB main-sequence stars (~ 8 - 25 Msol). The initial mass-accretion rates should have been high (10-4 - 10-3 Msol/yr) and the mYSOs likely represent a second-generation of massive star formation triggered by the O stars present in the center of the HII region.
L. Kaper, API, NL
B.B. Ochsendorf, Leiden, NL
L.E. Ellerbroek, API, NL
Suggested Session: Massive Star Formation