The most luminous stars in the Galaxy and the Magellanic Clouds
Wolf-Rainer Hamann, Andreas Barniske, Adriane Liermann, Lidia M. Oskinova, Diana Pasemann, Ute Rühling
Some of the Wolf-Rayet (WR) stars are found to have very high bolometric luminosities (log L/Lsun > 6). We employ the Potsdam Wolf-Rayet (PoWR) model atmospheres for their spectral analysis, which yields the bolometric corrections. Distance and interstellar reddening also enter the luminosity estimates. Among the Galactic stars, there is a group of very luminous WNL stars (i.e.\ WR stars of late subtype from nitrogen sequence with hydrogen being depleted in their atmosphere, but not absent). Their distance is often the major source of uncertainty. From K-band spectroscopy we found a very luminous star (log L/Lsun = 6.5) in the Galactic center region, which we termed the Peony Star because of the form of its surrounding dusty nebula. A similar group of very luminous WNL stars is found in the Large Magellanic Cloud (LMC). In the Small Magellanic Cloud (SMC) the majority of WR stars resides in binary systems. The single WNL stars in the SMC are not very luminous. We conclude that a significant number of very luminous WNL stars exist in the Galaxy and the LMC. With initial masses above 60 Msun, they apparently evolved directly to the WNL stage without a prior excursion to the red side of the HRD. At the low metallicity of the SMC, the binary channel may be dominant for the formation of WR stars.
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