Age spread in Galactic star forming region W3 Main
  We present near-infrared JHKs imaging as well as K-band multi-object spectroscopy of the massive stellar content of W3 Main using LUCI at the LBT. We confirm 13 OB stars by their absorption line spectra in W3 Main and spectral types between O5V and B4V have been found. Three massive Young Stellar Objects are identified by their emission line spectra and near-infrared excess. From our spectrophotometric analysis of the massive stars and the nature of their surrounding HII regions we derive the evolutionary sequence of W3 Main and we find an age spread of 2-3 Myr. 
A. Bik (1), Th. Henning (1), A. Stolte (2), W. Brandner (1), D. A.   Gouliermis (1), M. Gennaro (1), A. Pasquali (3), B. Roc...
astro-ph.GA