The Tarantula Massive Binary Monitoring

Shenar, T.; Richardson, Noel D.; Sablowski, D. P.; Hainich, R.; Sana, H.; Moffat, A. F. J.; Todt, H.; Hamann, Wolf-Rainer; Oskinova, L. M.; Sander, A. A. C.; Tramper, F.; Langer, N.; Bonanos, A. Z.; Mink, S. E. de; Gräfener, G.; Crowther, P. A.; Vink, J. S.; Almeida, L. A.; Koter, A. de; Barbá, R. H.; Herrero, A.; Ulaczyk, K.

doi:10.1051/0004-6361/201629621

Cited by 50 publications

(65 citation statements)

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“…M WR spec refers to the spectroscopic appearance of the He star, which primarily depends on the current mass-loss rate of the He star. It (Hainich et al 2014, gray circles), WN binaries (Gvaramadze et al 2014;Shenar et al 2016Shenar et al , 2017Shenar et al , 2018Shenar et al , 2019, gray circles surrounded by red circles), and the so-called LMC WN3/O3 stars (Neugent et al 2017, gray triangles). The MW sample includes only apparently-single WN stars .…”

Section: Wr Spec and M Wr Singlementioning

confidence: 99%

Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity

Shenar

Gilkis

Vink

et al. 2020

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101

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Context. Classical Wolf-Rayet (WR) stars are massive, hydrogen depleted, post main-sequence stars that exhibit emission-line dominated spectra. For a given metallicity Z, stars exceeding a certain initial mass M WR single (Z) can reach the WR phase through intrinsic mass-loss or eruptions (single-star channel). In principle, stars of lower masses can reach the WR phase via stripping through binary interactions (binary channel). Because winds become weaker at low Z, it is commonly assumed that the binary channel dominates the formation of WR stars in environments with low metallicity such as the Small and Large Magellanic Clouds (SMC, LMC). However, the reported WR binary fractions of 30 − 40% in the SMC (Z = 0.002) and LMC (Z = 0.006) are comparable to that of the Galaxy (Z = 0.014), and no evidence for the dominance of the binary channel at low Z could be identified observationally. Here, we explain this apparent contradiction by considering the minimum initial mass M WR spec (Z) needed for the stripped product to appear as a WR star. Aims. By constraining M WR spec (Z) and M WR single (Z), we estimate the importance of binaries in forming WR stars as a function of Z. Methods. We calibrate M WR spec (Z) using the lowest-luminosity WR stars in the Magellanic Clouds and the Galaxy. A range of M WR single values are explored using various evolution codes. We estimate the additional contribution of the binary channel by considering the interval [M WR spec (Z), M WR single (Z)], which characterizes the initial-mass range in which the binary channel can form additional WR stars. Results. The WR-phenomenon ceases below luminosities of log L≈4. 9, 5.25, and 5.6 [L ] in the Galaxy, the LMC, and the SMC, respectively, which translates to minimum He-star masses of 7.5, 11, 17 M and minimum initial masses of M WR spec = 18, 23, 37 M . Stripped stars with lower initial masses in the respective galaxies would tend to not appear as WR stars. The minimum mass necessary for self-stripping, M WR single (Z), is strongly model dependent, but lies in the range 20 − 30, 30 − 60, and 40 M for the Galaxy, LMC, and SMC, respectively. We find that that the additional contribution of the binary channel is a non-trivial and model-dependent function of Z that cannot be conclusively claimed to be monotonically increasing with decreasing Z. Conclusions. The WR spectral appearance arises from the presence of strong winds. Therefore, both M WR spec and M WR single increase with decreasing metallicity. Considering this, we show that one should not a-priori expect that binary interactions become increasingly important in forming WR stars at low Z, or that the WR binary fraction grows with decreasing Z.

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Section: Wr Spec and M Wr Singlementioning

confidence: 99%

Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity

Shenar

Gilkis

Vink

et al. 2020

A&A

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101

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“…Since the RVs of BAT99 32 and 77 could not be derived, we attempted their disentanglement using the code Spectangular, which is based on singular value decomposition in the wavelength domain (Sablowski & Weber 2017), first applied to WR stars in Shenar et al (2017). This procedure needs spectra spread over the orbital period and optimizes the orbital parameters or the RVs to minimize the residuals between the disentangled spectra and the observations.…”

Section: Spectral Disentanglementmentioning

confidence: 99%

“…However, given that the study relied on grids of models, we can estimate realistic statistical errors on the parameters. Regardless, the true error is dominated by systematic errors, which Article number, page 12 of 70 T. Shenar et al: The Wolf-Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud originate, among other things, in the uncertain wind velocity field (Gräfener & Hamann 2005;Sander et al 2017), clumping (Feldmeier 1995;Oskinova et al 2007;Sundqvist & Owocki 2013), atmosphere inflation (Gräfener et al 2012;Sanyal et al 2015;Grassitelli et al 2018;Ro 2019), and binary effects such as WWCs, mutual irradiation, and tidal deformations (Moffat et al 1988;Shenar et al 2017). It is our belief that the large number of analyzed systems compensates for these uncertainties.…”

Section: Errors From the Spectral Analysismentioning

confidence: 99%

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The Wolf–Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud

Shenar

Sablowski

Hainich

et al. 2019

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Context. Massive Wolf-Rayet (WR) stars dominate the radiative and mechanical energy budget of galaxies and probe a critical phase in the evolution of massive stars prior to core collapse. It is not known whether core He-burning WR stars (classical WR; cWR) form predominantly through wind stripping (w-WR) or binary stripping (b-WR). Whereas spectroscopy of WR binaries has so-far largely been avoided because of its complexity, our study focuses on the 44 WR binaries and binary candidates of the Large Magellanic Cloud (LMC; metallicity Z ≈ 0.5 Z ), which were identified on the basis of radial velocity variations, composite spectra, or high X-ray luminosities. Aims. Relying on a diverse spectroscopic database, we aim to derive the physical and orbital parameters of our targets, confronting evolution models of evolved massive stars at subsolar metallicity and constraining the impact of binary interaction in forming these stars. Methods. Spectroscopy was performed using the Potsdam Wolf-Rayet (PoWR) code and cross-correlation techniques. Disentanglement was performed using the code Spectangular or the shift-and-add algorithm. Evolutionary status was interpreted using the Binary Population and Spectral Synthesis (BPASS) code, exploring binary interaction and chemically homogeneous evolution. Results. Among our sample, 28/44 objects show composite spectra and are analyzed as such. An additional five targets show periodically moving WR primaries but no detected companions (SB1); two (BAT99 99 and 112) are potential WR + compact-object candidates owing to their high X-ray luminosities. We cannot confirm the binary nature of the remaining 11 candidates. About two-thirds of the WN components in binaries are identified as cWR, and one-third as hydrogen-burning WR stars. We establish metallicity-dependent mass-loss recipes, which broadly agree with those recently derived for single WN stars, and in which so-called WN3/O3 stars are clear outliers. We estimate that 45±30% of the cWR stars in our sample have interacted with a companion via mass transfer. However, only ≈12±7% of the cWR stars in our sample naively appear to have formed purely owing to stripping via a companion (12% b-WR). Assuming that apparently single WR stars truly formed as single stars, this comprises ≈ 4% of the whole LMC WN population, which is about ten times less than expected. No obvious differences in the properties of single and binary WN stars, whose luminosities extend down to log L≈5.2 [L ], are apparent. With the exception of a few systems (BAT99 19, 49, and 103), the equatorial rotational velocities of the OB-type companions are moderate (v eq 250 km s −1 ) and challenge standard formalisms of angular-momentum accretion. For most objects, chemically homogeneous evolution can be rejected for the secondary, but not for the WR progenitor. Conclusions. No obvious dichotomy in the locations of apparently single and binary WN stars on the Hertzsprung-Russell diagram is apparent. According to commonly used stellar evolution models (BPASS, Geneva), most a...

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“…Spectangular was published by Sablowski & Weber (2017) (hereafter Paper I); we point the reader to that article for the description of the program. The first application to highly variable Wolf-Rayet (WR) stars was presented in Shenar et al (2017). Spectangular is based on singular value decomposition (SVD) and runs in a downhill simplex optimization.…”

Section: Introductionmentioning

confidence: 99%

Spectangular: Disentangling variable spectra

Sablowski

Järvinen

Weber

2019

A&A

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Spectangular is a GUI based software package written in C++ designed for spectral disentangling on the wavelength scale. The code disentangles spectra of SB1 and SB2 systems and can now also be used also for spectra showing variability. In this work, effects of variability caused by telluric lines, line profile, and continuum flux are being investigated. Also shown is the disentangling on spectra from an artificial eclipsing binary. It is now possible to optimize on the flux ratios of each spectrum, making the disentangling a technique for extracting photometric information from spectroscopic observations usually provided by additional photometry. Furthermore, we make some comments about changes to the code since it was first published.

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The Tarantula Massive Binary Monitoring

Cited by 50 publications

References 105 publications

Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity

Why binary interaction does not necessarily dominate the formation of Wolf-Rayet stars at low metallicity

The Wolf–Rayet binaries of the nitrogen sequence in the Large Magellanic Cloud

Spectangular: Disentangling variable spectra

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