The Wolf-Rayet stars in M 31

Sander, A. A. C.; Todt, H.; Hainich, R.; Hamann, Wolf-Rainer

doi:10.1051/0004-6361/201323240

Cited by 29 publications

(36 citation statements)

References 47 publications

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“…Wind inhomogeneities are accounted for by means of the socalled mircoclumping approach, which assumes optically thin A&A 581, A21 (2015) (a) Asplund et al (2009); as used in Hamann et al (2006) and Sander et al (2014); (c) as used in Hainich et al (2014); Hunter et al (2007); (e) Korn et al (2000); ( f ) H ii regions (Kurt & Dufour 1998); (g) as adopted in this work; (h) including iron group elements; (i) mean value from Trundle et al (2007). clumps (Hillier 1991;Hamann & Koesterke 1998) that fill a volume fraction f V , while the interclump medium is void. The density contrast between the clumps and an homogeneous model with the same mass-loss rate is given by the clumping factor…”

Section: The Modelsmentioning

confidence: 99%

“…This theoretical prediction is supported by empirical studies (e.g., Bouret et al 2003;de Koter 2006;Mokiem et al 2007). For WR-stars, the situation is less clear since only a limited number of observational constraints ( In recent years, a large number of WN stars were spectroscopically analyzed in the MW (Hamann et al 2006;Martins et al 2008;Liermann et al 2010;Oskinova et al 2013); in M 31 (Sander et al 2014); and in the LMC , facilitating a comprehensive investigation of the relation between their wind mass-loss and metallicity. The averaged mass-loss rates of the WN stars in the MW, the late type WN stars in M 31, the WN stars in the LMC, and the SMC WN stars analyzed in this work are plotted in Fig.…”

Section: Metallicity Dependencementioning

confidence: 99%

“…When a specific parameter is not considered in the fit, it is depicted by a dash. In Table 5, the first line gives the coefficients obtained for the whole set of analyzed WN stars, comprising 153 putatively single WN stars from Hamann et al (2006), Martins et al (2008), Liermann et al (2010), Oskinova et al (2013), Sander et al (2014), and Hainich et al (2014). The mean deviation between the fit and the individual measurements is 0.27 dex and thus relatively large.…”

Section: Wn Mass-loss Prescriptionmentioning

confidence: 99%

“…However, a comprehensive evaluation of the metallicity effect on WR winds, considering a large number of objects from the Local Group Galaxies is still missing but imperative. The present study addresses this important problem, building on our recent analyses of WN stars in the Galaxy (Hamann et al 2006), M 31 (Sander et al 2014), and the LMC .…”

Section: Introductionmentioning

confidence: 99%

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Wolf-Rayet stars in the Small Magellanic Cloud

Hainich

Pasemann

Todt

et al. 2015

A&A

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159

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Context. Wolf-Rayet (WR) stars have a severe impact on their environments owing to their strong ionizing radiation fields and powerful stellar winds. Since these winds are considered to be driven by radiation pressure, it is theoretically expected that the degree of the wind mass-loss depends on the initial metallicity of WR stars. Aims. Following our comprehensive studies of WR stars in the Milky Way, M 31, and the LMC, we derive stellar parameters and massloss rates for all seven putatively single WN stars known in the SMC. Based on these data, we discuss the impact of a low-metallicity environment on the mass loss and evolution of WR stars. Methods. The quantitative analysis of the WN stars is performed with the Potsdam Wolf-Rayet (PoWR) model atmosphere code. The physical properties of our program stars are obtained from fitting synthetic spectra to multi-band observations. Results. In all SMC WN stars, a considerable surface hydrogen abundance is detectable. The majority of these objects have stellar temperatures exceeding 75 kK, while their luminosities range from 10 5.5 to 10 6.1 L . The WN stars in the SMC exhibit on average lower mass-loss rates and weaker winds than their counterparts in the Milky Way, M 31, and the LMC. Conclusions. By comparing the mass-loss rates derived for WN stars in different Local Group galaxies, we conclude that a clear dependence of the wind mass-loss on the initial metallicity is evident, supporting the current paradigm that WR winds are driven by radiation. A metallicity effect on the evolution of massive stars is obvious from the HRD positions of the SMC WN stars at high temperatures and high luminosities. Standard evolution tracks are not able to reproduce these parameters and the observed surface hydrogen abundances. Homogeneous evolution might provide a better explanation for their evolutionary past.

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Section: The Modelsmentioning

confidence: 99%

Section: Metallicity Dependencementioning

confidence: 99%

Section: Wn Mass-loss Prescriptionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Wolf-Rayet stars in the Small Magellanic Cloud

Hainich

Pasemann

Todt

et al. 2015

A&A

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111

159

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“…The hydrogen mass fraction can range from zero to ≈60% (e.g., Hamann et al 2006;Sander et al 2014). In the Galaxy and M 31, hydrogen-free WN stars are usually of early subtypes (WNE), while late subtype WN stars (WNL) typically show detectable hydrogen.…”

Section: The Gridsmentioning

confidence: 99%

Potsdam Wolf-Rayet model atmosphere grids for WN stars

Todt

Sander

Hainich

et al. 2015

A&A

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101

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We present new grids of Potsdam Wolf-Rayet (PoWR) model atmospheres for Wolf-Rayet stars of the nitrogen sequence (WN stars). The models have been calculated with the latest version of the PoWR stellar atmosphere code for spherical stellar winds. The WN model atmospheres include the non-LTE solutions of the statistical equations for complex model atoms, as well as the radiative transfer equation in the co-moving frame. Iron-line blanketing is treated with the help of the superlevel approach, while wind inhomogeneities are taken into account via optically thin clumps. Three of our model grids are appropriate for Galactic metallicity. The hydrogen mass fraction of these grids is 50%, 20%, and 0%, thus also covering the hydrogen-rich late-type WR stars that have been discovered in recent years. Three grids are adequate for LMC WN stars and have hydrogen fractions of 40%, 20%, and 0%. Recently, additional grids with SMC metallicity and with 60%, 40%, 20%, and 0% hydrogen have been added. We provide contour plots of the equivalent widths of spectral lines that are usually used for classification and diagnostics.

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Herschel/PACS: Constraining clumping in the intermediate wind region of OB stars

Rubio-Díez¹,

Najarro²,

Sundqvist

et al. 2014

Proc. IAU

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At present, it is well established that previously accepted mass-loss rates (Ṁ) of luminous OB stars may be overestimated when clumping is neglected. Our Herschel/PACS Far-Infrared (Far-IR) observations of a set of OB stars allow us to improve our knowledge of clumping stratification, constraining clumping properties in intermediate wind regions. In this work, better sampled clumping structure estimates are provided for ι Ori, ε Ori and ξ Per as well as an initial estimate of the clumping properties of the wind from τ Sco. These observations will allow us to obtain reliable mass-loss rates and improve our understanding of the wind physics.

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The Wolf-Rayet stars in M 31

Cited by 29 publications

References 47 publications

Wolf-Rayet stars in the Small Magellanic Cloud

Wolf-Rayet stars in the Small Magellanic Cloud

Potsdam Wolf-Rayet model atmosphere grids for WN stars

Herschel/PACS: Constraining clumping in the intermediate wind region of OB stars

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