2003) and the dominance of the binary channel in the SMC is still debated ( Shenar et al. The reported SMC WR binary fraction is similar to the Galactic WR binary fraction ( Foellmi et al. 2007) and a distance of 62 kpc ( Keller & Wood 2006), offers an ideal environment to test this. The Small Magellanic Cloud (SMC), with Z SMC ≈ 1∕7 Z ⊙ ( Trundle et al. 2015), it is expected that the binary formation channel should become dominant in low metallicity environments ( Maeder & Meynet 1994 Bartzakos et al. Since wind mass-loss rates Ṁ scale with metallicity Z ( Crowther & Hadfield 2006 Hainich et al. 2017), may lose their outer layers through mass transfer ( Paczynski 1973 Vanbeveren et al. Second, mass donors in binary systems, which are expected to be common (e.g., Kiminki & Kobulnicky 2012 Sana et al. First, single massive stars can lose their hydrogen-rich envelopes via powerful radiation-driven winds or eruptions ( Conti 1976). Two WR-star formation channels have been proposed. It is essential to improve our understanding of WR stars especially in the era of gravitational waves. Studying WR stars is important both for understanding the evolution of massive stars (e.g., Crowther 2007) and for constraining the energy budget of galaxies ( Ramachandran et al. Stars that are massive enough eventually reach the classical Wolf-Rayet (WR) phase that is characterized by powerful stellar winds and hydrogen depletion. The study of massive stars ( M i ≳ 8 M ⊙) and binaries at various metallicities is essential for a multitude of astrophysical fields, from supernovae physics to galactic evolution (e.g., Langer 2012). Key words: stars: massive / binaries: spectroscopic / stars: Wolf-Rayet / Magellanic Clouds / stars: individual: SMC AB 6 / stars: atmospheres This finding resolves the previously reported puzzle of the WR primary exceeding the Eddington limit and suggests that the WR star exchanged mass with its companion in the past. Our study shows that AB 6 is a multiple – probably quintuple – system. The WR binary likely experienced nonconservative mass transfer in the past supported by the relatively rapid rotation of star B.Ĭonclusions. We derive the initial masses of M i,WR = 60 M ⊙ and M i,O = 40 M ⊙ and an age of 3.9 Myr for the system. Correspondingly, the WR star does not exceed the Eddington limit. The WR star is found to be less luminous than previously thought (log L = 5.9 ) and, adopting M O = 41 M ⊙ for star B, more massive ( M WR = 18 M ⊙). We derive a mass ratio of M O∕ M WR = 2.2 ± 0.1. It is not clear that these additional components are bound to the WR binary. Star D appears to form a second 140 d period binary together with a fifth stellar member, which is a B-type dwarf or a black hole. Finally, narrow absorption lines portraying a long-term radial velocity variation show the existence of a fourth star (O7.5 V, star D). Static N III and N IV emission lines and absorption signatures in He lines suggest the presence of an early-type emission line star (O5.5 I(f), star C). The 6.5 d period WR binary comprises the WR primary (WN3:h, star A) and a rather rapidly rotating ( v eq = 265 km s −1) early O-type companion (O5.5 V, star B). The evolution of the system was analyzed using the Binary Population and Spectral Synthesis evolution code. We measured radial velocities via cross-correlation and performed a spectral analysis using the Potsdam Wolf-Rayet model atmosphere code. Through spectroscopy and orbital analysis of newly acquired optical data taken with the Ultraviolet and Visual Echelle Spectrograph (UVES), we aim to understand the peculiar results reported for this system and explore its evolutionary history. The WR component in AB 6 was previously found to be very luminous (log L = 6.3 ) compared to its reported orbital mass (≈8 M ⊙), placing it significantly above the Eddington limit.Īims. This binary is therefore a key system in the study of binary interaction and formation of WR stars at low metallicity. SMC AB 6 is the shortest-period ( P = 6.5 d) Wolf-Rayet (WR) binary in the Small Magellanic Cloud. Institut für Physik und Astronomie, Universität Potsdam,Į-mail: de physique and Centre de Recherche en Astrophysique du Québec (CRAQ), Université de Montréal,Īmerican Association of Variable Star Observers,Ĭontext. Astronomical objects: linking to databases.Including author names using non-Roman alphabets.Suggested resources for more tips on language editing in the sciences Punctuation and style concerns regarding equations, figures, tables, and footnotes
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