The Nature of Newly Discovered Wolf-Rayet Stars in the LMC

We have recently discovered five Wolf-Rayet (WR) stars in the LMC which might be naively classified as "WN3+O3 V." However, such a pairing is unlikely for a number of reasons: (a) O3 V stars are very rare, as they are the hottest and most luminous of the dwarfs; (b) the absolute visual magnitudes of our stars are quite faint (Mv=-3) compared to even an O3 V star by itself (Mv=-5.5); (c) these stars do not exhibit radial velocity variations, although our data on this are admittedly limited; and (d) such a pairing would be hard to understand from a stellar evolution point of view, since a massive star will evolve out of the O3 V phase in about a million years, while it takes several million years to form a WN star. We are forced to conclude that we have discoverd a new class of WRs. We have excellent optical spectra with Magellan, and our modeling of these data suggest a very high effective temperature (70,000 K), strongly enhanced nitrogen, and a very low mass-loss rate. However, these physical parameters are poorly constrained by the optical data alone, and we now seek UV spectra that will contain lines that will better determine the temperatures, and the important resonance lines that provide crucial diagnostics of the stellar winds. The results of this modeling will allow us to understand the nature of these objects, and where they fit in the evolution of massive stars. If they are the products of single star evolution, they indicate we have some fundamental misconceptions. If they are the products of binary evolution, how do we explain the absence of any companions? We can only address these questions by having reliable stellar parameters and abundances.