A Modern Search for Wolf-Rayet Stars in the Magellanic Clouds: First Results

TL;DR

This paper reports the first results of a new survey in the Magellanic Clouds that identified nine new Wolf-Rayet stars, including a rare WO-type, and discusses their characteristics and implications for stellar evolution.

Contribution

It introduces a novel survey method applied to the Magellanic Clouds and reports the discovery of new Wolf-Rayet stars, including rare types, expanding the known population.

Findings

Discovered 9 new Wolf-Rayet stars in the LMC, including one WO-type.

Identified unusual WN3 stars with absorption components, possibly from companions.

Detected rare Of?p stars and B[e] star with potential WN companion.

Abstract

Over the years, directed surveys and incidental spectroscopy have identified 12 Wolf-Rayet (WR) stars in the SMC and 139 in the LMC, numbers which are often described as "essentially} complete." Yet, new WRs are discovered in the LMC almost yearly. We have therefore initiated a new survey of both Magellanic Clouds using the same interference-filter imaging technique previously applied to M31 and M33. We report on our first observing season, in which we have successfully surveyed ~15$% of our intended area of the SMC and LMC. Spectroscopy has confirmed 9 newly found WRs in the LMC (a 6% increase), including one of WO-type, only the third known in that galaxy and the second to be discovered recently. The other eight are WN3 stars that include an absorption component. In two, the absorption is likely from an O-type companion, but the other six are quite unusual. Five would be classified naively as "WN3+O3 V," but such a pairing is unlikely given the rarity of O3 stars, the short duration of this phase (which is incommensurate with the evolution of a companion to a WN star), and because these stars are considerably fainter than O3 V stars. The sixth star may also fall into this category. CMFGEN modeling suggests these stars are hot, bolometrically luminous, and N-rich like other WN3 stars, but lack the strong winds that characterize WNs. Finally, we discuss two rare Of?p stars and four Of supergiants we found, and propose that the B[e] star HD 38489 may have a WN companion.