Spectroscopy of SMC Wolf-Rayet Stars Suggests that Wind Clumping Does Not Depend on Ambient Metallicity

Марченко, С. В.; Foellmi, C.; Moffat, A. F. J.; Martins, F.; Bouret, J. C.; Depagne, É.

doi:10.1086/512725

Cited by 15 publications

(14 citation statements)

References 27 publications

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“…We have demonstrated that the clumping factor is nearly the same in LMC and SMC as in our Galaxy. This agrees with observational studies that also found that the level of clumping does not depend on metallicity (Marchenko et al 2007, Mokiem et al 2007b). The observational dependence of mass-loss rate on luminosity in Fig.…”

Section: Calculated Global Wind Modelssupporting

confidence: 92%

Global hot-star wind models for stars from Magellanic Clouds

Krtička¹,

Kubát

2018

A&A

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We provide mass-loss rate predictions for O stars from Large and Small Magellanic Clouds. We calculate global (unified, hydrodynamic) model atmospheres of main sequence, giant, and supergiant stars for chemical composition corresponding to Magellanic Clouds. The models solve radiative transfer equation in comoving frame, kinetic equilibrium equations (also known as NLTE equations), and hydrodynamical equations from (quasi-)hydrostatic atmosphere to expanding stellar wind. The models allow us to predict wind density, velocity, and temperature (consequently also the terminal wind velocity and the mass-loss rate) just from basic global stellar parameters. As a result of their lower metallicity, the line radiative driving is weaker leading to lower wind mass-loss rates with respect to the Galactic stars. We provide a formula that fits the mass-loss rate predicted by our models as a function of stellar luminosity and metallicity. On average, the mass-loss rate scales with metallicity asṀ ∼ Z 0.59 . The predicted mass-loss rates are lower than mass-loss rates derived from Hα diagnostics and can be reconciled with observational results assuming clumping factor Cc = 9. On the other hand, the predicted mass-loss rates either agree or are slightly higher than the mass-loss rates derived from ultraviolet wind line profiles. The calculated P v ionization fractions also agree with values derived from observations for LMC stars with T eff ≤ 40 000 K. Taken together, our theoretical predictions provide reasonable models with consistent mass-loss rate determination, which can be used for quantitative study of stars from Magellanic Clouds.

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Section: Calculated Global Wind Modelssupporting

confidence: 92%

Global hot-star wind models for stars from Magellanic Clouds

Krtička¹,

Kubát

2018

A&A

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“…Studies confirm that massive star winds are also clumped at low metallicities (Marchenko et al 2007). This implies that empirically derived mass-loss rates corrected for clumping would be lower than those obtained using the standard recipe.…”

Section: Metallicity Clumping and Mass-loss Ratementioning

confidence: 91%

Observational properties of massive black hole binary progenitors

Hainich¹,

Oskinova²,

Shenar³

et al. 2018

A&A

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Context. The first directly detected gravitational waves (GW 150914) were emitted by two coalescing black holes (BHs) with masses of ≈ 36 M and ≈ 29 M . Several scenarios have been proposed to put this detection into an astrophysical context. The evolution of an isolated massive binary system is among commonly considered models. Aims. Various groups have performed detailed binary-evolution calculations that lead to BH merger events. However, the question remains open as to whether binary systems with the predicted properties really exist. The aim of this paper is to help observers to close this gap by providing spectral characteristics of massive binary BH progenitors during a phase where at least one of the companions is still non-degenerate. Methods. Stellar evolution models predict fundamental stellar parameters. Using these as input for our stellar atmosphere code (PoWR), we compute a set of models for selected evolutionary stages of massive merging BH progenitors at different metallicities. Results. The synthetic spectra obtained from our atmosphere calculations reveal that progenitors of massive BH merger events start their lives as O2-3V stars that evolve to early-type blue supergiants before they undergo core-collapse during the Wolf-Rayet phase. When the primary has collapsed, the remaining system will appear as a wind-fed high-mass X-ray binary. Based on our atmosphere models, we provide feedback parameters, broad band magnitudes, and spectral templates that should help to identify such binaries in the future. Conclusions. While the predicted parameter space for massive BH binary progenitors is partly realized in nature, none of the known massive binaries match our synthetic spectra of massive BH binary progenitors exactly. Comparisons of empirically determined mass-loss rates with those assumed by evolution calculations reveal significant differences. The consideration of the empirical massloss rates in evolution calculations will possibly entail a shift of the maximum in the predicted binary-BH merger rate to higher metallicities, that is, more candidates should be expected in our cosmic neighborhood than previously assumed.Article number, page 2 of 64 R. Hainich et al.: Observational properties of massive black hole binary progenitors Track II 50 M Z /20 Track I 60 M Z /10 pre WR phase WN: 55 % ≥ XH > 5 % WN: XH ≤ 5 % WC/WO phase overcontact phase MII 1 MI 1 MII 2 MI 2 MII 3 MI 3 MII 4 MI 4 MI 5 MII 5 T * /kK 40 60 100 150

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“…be slightly stronger than in our models. Marchenko et al (2007) concluded that there is no metallicity dependence of the clumping properties but their conclusion is based on a small sample of Wolf-Rayet stars. In addition these objects have winds that do not behave exactly as those of OB stars (e.g., Sander et al 2017).…”

Section: Metallicity Of the Small Magellanic Cloudmentioning

confidence: 98%

Spectroscopic evolution of massive stars near the main sequence at low metallicity

Martins

2021

A&A

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Context. The evolution of massive stars is not fully understood. Several physical processes affect their life and death, with major consequences on the progenitors of core-collapse supernovae, long-soft gamma-ray bursts, and compact-object mergers leading to gravitational wave emission. Aims. In this context, our aim is to make the prediction of stellar evolution easily comparable to observations. To this end, we developed an approach called “spectroscopic evolution” in which we predict the spectral appearance of massive stars through their evolution. The final goal is to constrain the physical processes governing the evolution of the most massive stars. In particular, we want to test the effects of metallicity. Methods. Following our initial study, which focused on solar metallicity, we investigated the low Z regime. We chose two representative metallicities: 1/5 and 1/30 Z⊙. We computed single-star evolutionary tracks with the code STAREVOL for stars with initial masses between 15 and 150 M⊙. We did not include rotation, and focused on the main sequence (MS) and the earliest post-MS evolution. We subsequently computed atmosphere models and synthetic spectra along those tracks. We assigned a spectral type and luminosity class to each synthetic spectrum as if it were an observed spectrum. Results. We predict that the most massive stars all start their evolution as O2 dwarfs at sub-solar metallicities contrary to solar metallicity calculations and observations. The fraction of lifetime spent in the O2V phase increases at lower metallicity. The distribution of dwarfs and giants we predict in the SMC accurately reproduces the observations. Supergiants appear at slightly higher effective temperatures than we predict. More massive stars enter the giant and supergiant phases closer to the zero-age main sequence, but not as close as for solar metallicity. This is due to the reduced stellar winds at lower metallicity. Our models with masses higher than ∼60 M⊙ should appear as O and B stars, whereas these objects are not observed, confirming a trend reported in the recent literature. At Z = 1/30 Z⊙, dwarfs cover a wider fraction of the MS and giants and supergiants appear at lower effective temperatures than at Z = 1/5 Z⊙. The UV spectra of these low-metallicity stars have only weak P Cygni profiles. He II 1640 sometimes shows a net emission in the most massive models, with an equivalent width reaching ∼1.2 Å. For both sets of metallicities, we provide synthetic spectroscopy in the wavelength range 4500−8000 Å. This range will be covered by the instruments HARMONI and MOSAICS on the Extremely Large Telescope and will be relevant to identify hot massive stars in Local Group galaxies with low extinction. We suggest the use of the ratio of He I 7065 to He II 5412 as a diagnostic for spectral type. Using archival spectroscopic data and our synthetic spectroscopy, we show that this ratio does not depend on metallicity. Finally, we discuss the ionizing fluxes of our models. The relation between the hydrogen ionizing flux per unit area versus effective temperature depends only weakly on metallicity. The ratios of He I and He II to H ionizing fluxes both depend on metallicity, although in a slightly different way. Conclusions. We make our synthetic spectra and spectral energy distributions available to the community.

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Spectroscopy of SMC Wolf-Rayet Stars Suggests that Wind Clumping Does Not Depend on Ambient Metallicity

Cited by 15 publications

References 27 publications

Global hot-star wind models for stars from Magellanic Clouds

Global hot-star wind models for stars from Magellanic Clouds

Observational properties of massive black hole binary progenitors

Spectroscopic evolution of massive stars near the main sequence at low metallicity

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