WR 20a: A massive cornerstone binary system comprising two extreme early-type stars

Rauw, Grégor; Becker, M. De; Nazé, Yaël; Crowther, P. A.; Gosset, Éric; Sana, H.; Hucht, K. van der; Vreux, Jean-Marie; Williams, P. M.

doi:10.1051/0004-6361:20040150

Cited by 119 publications

(134 citation statements)

References 18 publications

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“…-Two additional examples of very massive stars in elliptical orbits whose large eccentricity made the discovery of their binarity difficult are WR 22 ≡ HD 92 740 (Moffat & Seggewiss 1978;Conti et al 1979;Schweickhardt et al 1999, WN7 + O8-9.5 III:) and HD 93 162 (Gamen et al 2008;Sota et al 2014, O2.5 If*/WN6 + OB). -There are also very massive twin systems in shorter, nearcircular orbits such as NGC 3603-A1 (Moffat et al 2004;Schnurr et al 2008, WN6ha + WN6ha), WR 20a (Rauw et al 2004;Bonanos et al 2004;Crowther & Walborn 2011 we note that σ Ori B is B0.5 V). Why were these systems not discovered earlier?…”

Section: Discussionmentioning

confidence: 63%

The little-studied cluster Berkeley 90

Apellániz

Negueruela

Barbá

et al. 2015

A&A

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Context. It appears that most (if not all) massive stars are born in multiple systems. At the same time, the most massive binaries are hard to find owing to their low numbers throughout the Galaxy and the implied large distances and extinctions. Aims. We want to study LS III +46 11, identified in this paper as a very massive binary; another nearby massive system, LS III +46 12; and the surrounding stellar cluster, Berkeley 90. Methods. Most of the data used in this paper are multi-epoch high S/N optical spectra, although we also use Lucky Imaging and archival photometry. The spectra are reduced with dedicated pipelines and processed with our own software, such as a spectroscopicorbit code, CHORIZOS, and MGB. Results. LS III +46 11 is identified as a new very early O-type spectroscopic binary [O3.5 If* + O3.5 If*] and LS III +46 12 as another early O-type system [O4.5 V((f))]. We measure a 97.2-day period for LS III +46 11 and derive minimum masses of 38.80 ± 0.83 M and 35.60 ± 0.77 M for its two stars. We measure the extinction to both stars, estimate the distance, search for optical companions, and study the surrounding cluster. In doing so, a variable extinction is found as well as discrepant results for the distance. We discuss possible explanations and suggest that LS III +46 12 may be a hidden binary system where the companion is currently undetected.

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Section: Discussionmentioning

confidence: 63%

The little-studied cluster Berkeley 90

Apellániz

Negueruela

Barbá

et al. 2015

A&A

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“…However, given that it appears significantly less massive than the WN6ha + WN6ha binary WR20a (m 1 = m 2 = 83 M , Rauw et al 2004;Bonanos et al 2004) we suspect that it will instead evolve to resemble Cyg OB2 #5 and hence to a configuration similar to GCIRS 16SW, composed Negueruela et al (2008), based on published spectral classes and 2MASS JHK S photometry and a DM of 11.3. The continuous lines are non-rotating isochrones for log t = 6.2, 6.3 and 6.4 from Schaller et al (1992) and the dashed line is the log t = 6.4 isochrone in the high-rotation models from Meynet & Maeder (2003).…”

Section: Discussionmentioning

confidence: 99%

The eclipsing, double-lined, Of supergiant binary Cygnus OB2-B17

Stroud

Clark

Negueruela

et al. 2010

A&A

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Context. Massive, eclipsing, double-lined, spectroscopic binaries are not common but are necessary to understand the evolution of massive stars as they are the only direct way to determine stellar masses. They are also the progenitors of energetic phenomena such as X-ray binaries and γ-ray bursts.Aims. We present a photometric and spectroscopic analysis of the candidate binary system Cyg OB2-B17 to show that it is indeed a massive evolved binary. Methods. We utilise V band and white-light photometry to obtain a light curve and period of the system, and spectra at different resolutions to calculate preliminary orbital parameters and spectral classes for the components. Results. Our results suggest that B17 is an eclipsing, double-lined, spectroscopic binary with a period of 4.0217 ± 0.0004 days, with two massive evolved components with preliminary classifications of O7 and O9 supergiants. The radial velocity and light curves are consistent with a massive binary containing components with similar luminosities, and in turn with the preliminary spectral types and age of the association.

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“…These observations revealed strong evidence of ongoing star formation activity and underlined the need for a detailed study of the properties of the early-type stars in the cluster core and their impact on the surrounding nebula. On the other hand, WR 20a -one of the two Wolf-Rayet stars in RCW 49 -was found to be a very massive eclipsing binary consisting of two WN6ha stars with individual masses of about 80 M (Rauw et al 2004(Rauw et al , 2005Bonanos et al 2004). Since previous spectroscopic studies revealed only one O6: and six O7: stars, in the cluster core , the existence of a pair of stars that massive was somewhat unexpected.…”

Section: Introductionmentioning

confidence: 96%

A spectroscopic investigation of early-type stars in the young open cluster Westerlund 2

Rauw

Sana

Nazé

2011

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Context. The distance of the very young open cluster Westerlund 2, which contains the very massive binary system WR 20a and is likely associated with a TeV source, has been the subject of much debate. Aims. We attempt a joint analysis of spectroscopic and photometric data of eclipsing binaries in the cluster to constrain its distance. Methods. A sample of 15 stars, including three eclipsing binaries (MSP 44, MSP 96, and MSP 223) was monitored with the FLAMES multi-object spectrograph. The spectroscopic data are analysed together with existing B V photometry.Results. The analysis of the three eclipsing binaries clearly supports the larger values of the distance, around 8 kpc, and rules out values of about 2.4−2.8 kpc that have been suggested in the literature. Furthermore, our spectroscopic monitoring reveals no clear signature of binarity with periods shorter than 50 days in either the WN6ha star WR 20b, the early O-type stars MSP 18, MSP 171, MSP 182, MSP 183, MSP 199, and MSP 203, or three previously unknown mid O-type stars. The only newly identified candidate binary system is MSP 167. The absence of a binary signature is especially surprising for WR 20b and MSP 18, which were previously found to be bright X-ray sources. Conclusions. The distance of Westerlund 2 is confirmed to be around 8 kpc as previously suggested based on the spectrophotometry of its population of O-type stars and the analysis of the light curve of WR 20a. Our results suggest that short-period binary systems are not likely to be common, at least not among the population of O-type stars in the cluster.

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WR 20a: A massive cornerstone binary system comprising two extreme early-type stars

Cited by 119 publications

References 18 publications

The little-studied cluster Berkeley 90

The little-studied cluster Berkeley 90

The eclipsing, double-lined, Of supergiant binary Cygnus OB2-B17

A spectroscopic investigation of early-type stars in the young open cluster Westerlund 2

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