A Deep Survey for Galactic Wolf-Rayet Stars. II. Implications for Galactic Structure and Massive Star Formation

Shara, Michael M.; Moffat, A. F. J.; Smith, Lindsey F.; Niemelä, Virpi Sinikka; Potter, Michael; Lamontagne, R.

doi:10.1086/300908

Cited by 48 publications

(68 citation statements)

References 24 publications

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“…The WN spectrum was already classified as WN6 by Shara et al (1991) and later reclassified as WN6h by Shara et al (1999). We agree with the later classification.…”

Section: Resultssupporting

confidence: 84%

WR 35a: A new double-lined spectroscopic binary

Gamen

Collado

Barbá

et al. 2014

A&A

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Aims. We present the first orbital solution for the Wolf-Rayet star, WR 35a, that was discovered by a spectroscopic monitoring of faint WN-type stars. Methods. Spectral features of two different components were identified, and thus a method of disentangling the individual spectra of both components was applied. Radial velocities were determined for each component in the binary system. Results. The orbital solution and component properties of the system were derived. We determined that WR 35a is composed of a WN6 star with a O8.5 V companion orbiting at a 41.90-day period.

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“…The WN spectrum was already classified as WN6 by Shara et al (1991) and later reclassified as WN6h by Shara et al (1999). We agree with the later classification.…”

Section: Resultssupporting

confidence: 84%

WR 35a: A new double-lined spectroscopic binary

Gamen

Collado

Barbá

et al. 2014

A&A

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“…The use of narrow-band selection techniques was pioneered by Massey & Conti (1983) and Moffat & Shara (1983) to identify extra-galactic WR stars, taking advantage of strong WR star emission lines at optical wavelengths. Shara et al (1991Shara et al ( , 1999 applied similar methods to push the extent of the known Galactic population beyond 5 kpc from the Sun, and extension to near-IR wavelengths has facilitated yet deeper investigation of the Galactic disk (Shara et al 2009(Shara et al , 2012. Another distinctive feature of WR stars -the near-IR excess caused by free-free emission in their winds -has been exploited to yield further discoveries (Homeier et al 2003;Hadfield et al 2007;Mauerhan, Van Dyk & Morris 2011).…”

Section: Introductionmentioning

confidence: 99%

“…Maeder & Lequeux (1982) used the then-known 157 WR stars to arrive at a total of ∼1,200 by assuming the surface density of WR stars to vary with Galactocentric radius (RG) in the same way as giant HII-regions, including a dearth at RG 3kpc. To emphasise the need for IR investigation, Shara et al (1999) created a model WR star population featuring a stellar disk of exponentially increasing density towards RG = 0. From this they inferred a total of 2,500 Galactic WR stars, or 1,500 if few WR stars inhabit the region RG 3kpc, as the decline in gas density suggests (barring the inner 500 pc).…”

Section: Introductionmentioning

confidence: 99%

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

Rosslowe

Crowther

2015

Monthly Notices of the Royal Astronomical Society

119

143

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We construct revised near-infrared absolute magnitude calibrations for 126 Galactic Wolf-Rayet (WR) stars at known distances, based in part upon recent large scale spectroscopic surveys. Application to 246 WR stars located in the field, permits us to map their Galactic distribution. As anticipated, WR stars generally lie in the thin disk (∼40 pc half width at half maximum) between Galactocentric radii 3.5-10 kpc, in accordance with other star formation tracers. We highlight 12 WR stars located at vertical distances of 300 pc from the midplane. Analysis of the radial variation in WR subtypes exposes a ubiquitously higher N W C /N W N ratio than predicted by stellar evolutionary models accounting for stellar rotation. Models for non-rotating stars or accounting for close binary evolution are more consistent with observations. We consolidate information acquired about the known WR content of the Milky Way to build a simple model of the complete population. We derive observable quantities over a range of wavelengths, allowing us to estimate a total number of 1200 +300 −100 Galactic WR stars, implying an average duration of ∼ 0.25 Myr for the WR phase at the current Milky Way star formation rate. Of relevance to future spectroscopic surveys, we use this model WR population to predict follow-up spectroscopy to K S ≃ 13 mag will be necessary to identify 95% of Galactic WR stars. We anticipate that ESA's Gaia mission will make few additional WR star discoveries via low-resolution spectroscopy, though will significantly refine existing distance determinations. Appendix A provides a complete inventory of 322 Galactic WR stars discovered since the VIIth catalogue (313 including Annex), including a revised nomenclature scheme.

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“…The presence of this line in the spectrum of WR 20a along with the weakness of He  λ 5876 was first noted by Shara et al (1999) who classified WR 20a accordingly as a WN7:h/C star. Finally, we note that the He  λ 5412 line is seen in absorption.…”

Section: The Optical Spectrum Of Wr 20amentioning

confidence: 82%

The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions

Rauw¹,

Crowther

Becker³

et al. 2005

A&A

137

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Abstract. We analyse the optical spectrum of the very massive binary system WR 20a (WN6ha + WN6ha). The most prominent emission lines, Hα and He  λ 4686, display strong phase-locked profile variability. From the variations of their equivalent widths and from a tomographic analysis, we find that part of the line emission probably arises in a wind interaction region between the stars. Our analysis of the optical spectrum of WR 20a indicates a reddening of A V 6.0 mag and a distance of ∼7.9 kpc, suggesting that the star actually belongs to the open cluster Westerlund 2. The location of the system at ∼1.1 pc from the cluster core could indicate that WR 20a was gently ejected from the core via dynamical interactions. Using a non-LTE model atmosphere code, we derive the fundamental parameters of each component: T eff = 43 000 ± 2000 K, log L bol /L 6.0,Ṁ = 8.5 × 10 −6 M yr −1 (assuming a clumped wind with a volume filling factor f = 0.1). Nitrogen is enhanced in the atmospheres of the components of WR 20a, while carbon is definitely depleted. Finally, the position of the binary components in the Hertzsprung-Russell diagram suggests that they are core hydrogen burning stars in a pre-LBV stage and their current atmospheric chemical composition probably results from rotational mixing that might be enhanced in a close binary compared to a single star of same age.

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A Deep Survey for Galactic Wolf-Rayet Stars. II. Implications for Galactic Structure and Massive Star Formation

Cited by 48 publications

References 24 publications

WR 35a: A new double-lined spectroscopic binary

WR 35a: A new double-lined spectroscopic binary

Spatial distribution of Galactic Wolf–Rayet stars and implications for the global population

The spectrum of the very massive binary system WR 20a (WN6ha + WN6ha): Fundamental parameters and wind interactions

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