Uniformity of the WC stars in the Large Magellanic Cloud

Smith, Lindsey F.; Shara, Michael M.; Moffat, A. F. J.

doi:10.1086/168256

Cited by 54 publications

(54 citation statements)

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“…the six studied by Crowther et al (2002) in Table 2. Our results support the conclusions of Smith et al (1990a) that the average C iv λ5808 line luminosity of LMC WC stars is 3.2 × 10 36 erg/s, using an increased sample.…”

Section: IV λ5808 In Wc Starssupporting

confidence: 91%

Reduced Wolf-Rayet line luminosities at low metallicity

Crowther¹,

Hadfield²

2006

A&A

135

222

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New NTT/EMMI spectrophotometry of single WN2-5 stars in the Small and Large Magellanic Clouds are presented, from whichHe ii λ4686 line luminosities have been derived, and compared with observations of other Magellanic Cloud Wolf-Rayet stars. SMC WN3-4 stars possess line luminosities which are a factor of 4 times lower than LMC counterparts, incorporating several binary SMC WN3-4 stars from the literature. Similar results are found for WN5-6 stars, despite reduced statistics, incorporating observations of single LMC WN5-9 stars from the literature. C iv λ5808 line luminosities of carbon sequence WR stars in the SMC and IC 1613 (both WO subtypes) from the recent literature are a factor of 3 lower than LMC WC stars from Mt Stromlo/DBS spectrophotometry, although similar results are also obtained for the sole LMC WO star. We demonstrate how reduced line luminosities at low metallicity follow naturally if WR winds are metallicity-dependent, as recent empirical and theoretical results suggest. We apply mass loss-metallicity scalings to atmospheric non-LTE models of Milky Way and LMC WR stars to predict the wind signatures of WR stars in the metal-poor star forming WR galaxy I Zw 18. WN He ii λ4686 line luminosities are 7-20 times lower than in metal-rich counterparts of identical bolometric luminosity, whilst WC C iv λ5808 line luminosities are 3-6 times lower. Significant He + Lyman continuum fluxes are predicted for metal-poor early-type WR stars. Consequently, our results suggest a larger population of WR stars in I Zw 18 than is presently assumed, particularly for WN stars, potentially posing a severe challenge to evolutionary models at very low metallicity. Finally, reduced wind strengths from WR stars at low metallicities impacts upon the immediate circumstellar environment of long duration GRB afterglows, particularly since the host galaxies of high-redshift GRBs tend to be metal-poor.

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Section: IV λ5808 In Wc Starssupporting

confidence: 91%

Reduced Wolf-Rayet line luminosities at low metallicity

Crowther¹,

Hadfield²

2006

A&A

135

222

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“…WCE stars are usually represented by WC4 stars. The average C IV 5808 Å line luminosity of LMC WC stars is 3.2×10 36 erg s −1 (Smith et al 1990;Crowther & Hadfield 2006).…”

Section: Identifying the Subtypes Of Wr Stars And Estimating Their Numentioning

confidence: 98%

The Wolf-Rayet features and mass–metallicity relation of long-duration gamma-ray burst host galaxies

Han

Hammer²,

Liang

et al. 2010

A&A

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Aims. We gather optical spectra of 8 long-duration GRB host galaxies selected from the archival data of VLT/FORS2. We investigate whether or not Wolf-Rayet (WR) stars can be detected in these GRB host galaxies. We also estimate the physical properties of GRB host galaxies, such as metallicity. Methods. We identify the WR features in these spectra by fitting the WR bumps and WR emission lines in blue and red bumps. We identify the subtypes of the WR stars, estimate the numbers of stars in each subtype, and calculate the WR/O star ratios. The (O/H) abundances of GRB hosts are inferred from both the electron temperature (T e ) and the metallicity-sensitive strong-line ratio (R 23 ), for which we break the R 23 degeneracy. We compare the environments of long-duration GRB host galaxies with those of other galaxies in terms of their luminosity (stellar mass)-metallicity relations (L−Z, M * −Z). Results. We detect WR stars in 5 GRB host galaxies with spectra of relatively high signal-to-noise ratios (S /N). In the comparison of L−Z, M * −Z relations, we show that GRB hosts have lower metallicities than other samples of comparable luminosity and stellar mass. The presence of WR stars and the observed high WR/O star ratio, together with the low metallicity, support the "core-collapsar" model and imply that we are witnessing the first stage of star formation in the host regions of GRBs.

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“…At first sight this might suggest that HD 191765 should be more properly classified as a WN4 star. However, the Smith et al (1990) three-dimensional optical classification scheme for WN stars incorporates an assessment of (i) ionization state, based on relative line intensities of N iii-v, (ii) the presence or absence of hydrogen-the ''h'' designation, and (iii) line widths, distinguishing broad (b) and narrow emission line spectra. The close morphological similarity between HD 191765 and HD 187282 is due to high wind densities in both cases, albeit with differing ionization.…”

Section: Wn6-wn7 Spectra: Figg Ures 3a and 3bmentioning

confidence: 99%

An Atlas of Far‐Ultraviolet Spectra of Wolf‐Rayet Stars from the FUSE Satellite

Willis¹,

Crowther²,

Fullerton³

et al. 2004

ASTROPHYS J SUPPL S

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We present an atlas of far-ultraviolet spectra of 21 Wolf-Rayet (WR) stars in the Galaxy and Large and Small Magellanic Clouds, secured with the Far Ultraviolet Spectroscopic Explorer (FUSE) satellite. The data cover the wavelength range of 912-1190 8 at a spectral resolution of 0.1 8 and span examples of most subtypes in the WN and WC sequences. We discuss the FUV spectral morphology of the different WR sequences, emphasizing the wide range of ions and chemical species exhibiting well-developed P Cygni profiles and emission lines in this wavelength range. For WN stars the relative strengths of C iv/C iii, N iii /N ii, P v/P iv, and Si iv/Si iii show a decrease in strength of the high ions from WN3 to WN11 complemented by an increase in the lower ions at later types. The ''super ions'' of O vi and S vi are considered photoionized wind features for WN3-WN6 stars, probably the result of Auger ionization in WN7-WN9 stars, and probably absent at WN10-WN11. The WN5h star Sk 41 in the SMC shows relatively weaker features, which can be ascribed to the effects of a global galaxy metal deficiency. For the WC stars, a similar pattern of wind ionization-linked strengths in the emissions and P Cygni profiles is present, particularly evident in the relative strengths of lines in P v, S iv, Si iv, and Si iii. O vi, and S vi features are only seen in the earliest WC subtypes. The high carbon abundance in WC stars is reflected by the presence of strong C iv and C iii lines throughout the sequence. We present new estimates of the wind terminal velocities from measurements of saturated absorption components observed in a wide range of I.P. species. Considerable revisions to v 1 for the WN3 and WN5 (SMC) stars in our sample and, in particular for the WN10 and WN11 stars are found. The latter make use of the unique availability of the N ii resonance line in the FUSE waveband.

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Uniformity of the WC stars in the Large Magellanic Cloud

Cited by 54 publications

References 0 publications

Reduced Wolf-Rayet line luminosities at low metallicity

Reduced Wolf-Rayet line luminosities at low metallicity

The Wolf-Rayet features and mass–metallicity relation of long-duration gamma-ray burst host galaxies

An Atlas of Far‐Ultraviolet Spectra of Wolf‐Rayet Stars from the FUSE Satellite

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