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Abstract LMCe055-1 was recently discovered in a survey for Wolf–Rayets (WRs) in the Large Magellanic Cloud, and classified as a WN4/O4, a lower-excitation version of the WN3/O3 class discovered as part of the same survey. Its absolute magnitude precluded it from being a WN4+O4 binary. Optical Gravitational Lensing Experiment photometry shows shallow primary and secondary eclipses with a 2.2 days period. The spectral characteristics and short period pointed to a possible origin due to binary stripping. Such stripped WR binaries should be common but have proven elusive to identify conclusively. In order to establish its nature, we obtained Hubble Space Telescope ultraviolet and Magellan optical spectra, along with imaging. Our work shows that the WR emission and Heiiabsorption arise in one star, and the Heiabsorption in another. The Heicontributor is the primary of the 2.2 days system and exhibits ∼300 km s−1radial velocity variations on that timescale. However, the WR star shows 30–40 km s−1radial velocity variations, with a likely 35 days period and a highly eccentric orbit. Possibly LMCe055-1 is a physical triple, but that would require the 2.2 days pair to have been captured by the WR star. A more likely explanation is that the WR star has an unseen companion in a 35 days orbit and that the 2.2 days pair is in a longer-period orbit about the two. Such examples of multiple systems are well known among massive stars, such as HD 5980. Regardless, we argue that it is highly unlikely that the WR component of the LMCe055-1 system resulted from stripping.
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Constraints on the Binarity of the WN3/O3 Class of Wolf–Rayet Stars*
Abstract The WN3/O3 Wolf–Rayet (WR) stars were discovered as part of our survey for WRs in the Magellanic Clouds. The WN3/O3s show the emission lines of a high-excitation WN star and the absorption lines of a hot O-type star, but our prior work has shown that the absorption spectrum is intrinsic to the WR star. Their place in the evolution of massive stars remains unclear. Here we investigate the possibility that they are the products of binary evolution. Although these are not WN3+O3 V binaries, they could still harbor unseen companions. To address this possibility, we have conducted a multiyear radial velocity study of six of the nine known WN3/O3s. Our study finds no evidence of statistically significant radial velocity variations, and allows us to set stringent upper limits on the mass of any hypothetical companion star: for probable orbital inclinations, any companion with a period less than 100 days must have a mass <2M⊙. For periods less than 10 days, any companion would have to have a mass <1M⊙. We argue that scenarios where any such companion is a compact object are unlikely. The absorption lines indicate a normal projected rotational velocity, making it unlikely that these stars evolved with the aid of a companion star that has since merged. The modest rotation also suggests that these stars are not the result of homogenous evolution. Thus it is likely that these stars are a normal but short-lived stage in the evolution of massive stars.
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- Award ID(s):
- 1612874
- PAR ID:
- 10408892
- Publisher / Repository:
- DOI PREFIX: 10.3847
- Date Published:
- Journal Name:
- The Astrophysical Journal
- Volume:
- 947
- Issue:
- 2
- ISSN:
- 0004-637X
- Format(s):
- Medium: X Size: Article No. 77
- Size(s):
- Article No. 77
- Sponsoring Org:
- National Science Foundation
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