Sara Beck (Tel Aviv)
Looking for the Most Massive Stars

Massive O stars are the most important and influential in galaxy
evolution. Yet they are the hardest to study: they evolve so fast that
they can spend their entire lives embedded in the natal molecular
cloud.  So the simple question, what is the most massive star made, is
far from answered. We review the situation, describe the use of
infrared nebular diagnostics and some of their perplexing results, and
focus on the problem of spatial confusion in the search for massive
stars.  If the most massive stars are found in the compact dense
embedded clusters, they will escape detection even with SPITZER
observations -- unless treated properly.