Effect of rotational mixing and metallicity on the hot star wind mass-loss rates

Krtička, Jiřı́; Kubát, Jiřı́

doi:10.1051/0004-6361/201423845

Cited by 9 publications

(10 citation statements)

References 31 publications

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“…which provides a relatively accurate approximation for our results with a typical error of about 10−20%. Predicted mass-loss rates from our global models agree with those derived from our older purely wind models with fixed atmospheric structure (Krtička & Kubát 2014) for stars with low luminosity and low mass-loss ratesṀ 10 −7 M yr −1 . For more luminous stars the global models give mass-loss rates roughly a factor of two lower than the purely wind models.…”

Section: Mass-loss Ratessupporting

confidence: 75%

Comoving frame models of hot star winds

Krtička

Kubát

2017

A&A

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101

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We calculate global (unified) wind models of main-sequence, giant, and supergiant O stars from our Galaxy. The models are calculated by solving hydrodynamic, kinetic equilibrium (also known as NLTE) and comoving frame (CMF) radiative transfer equations from the (nearly) hydrostatic photosphere to the supersonic wind. For given stellar parameters, our models predict the photosphere and wind structure and in particular the wind mass-loss rates without any free parameters. Our predicted mass-loss rates are by a factor of 2-5 lower than the commonly used predictions. A possible cause of the difference is abandoning of the Sobolev approximation for the calculation of the radiative force, because our models agree with predictions of CMF NLTE radiative transfer codes. Our predicted mass-loss rates agree nicely with the mass-loss rates derived from observed near-infrared and X-ray line profiles and are slightly lower than mass-loss rates derived from combined UV and Hα diagnostics. The empirical mass-loss rate estimates corrected for clumping may therefore be reconciled with theoretical predictions in such a way that the average ratio between individual massloss rate estimates is not higher than about 1.6. On the other hand, our predictions are by factor of 4.7 lower than pure Hα mass-loss rate estimates and can be reconciled with these values only assuming a microclumping factor of at least eight.

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Section: Mass-loss Ratessupporting

confidence: 75%

Comoving frame models of hot star winds

Krtička

Kubát

2017

A&A

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101

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“…However, in the absence of actual observations of TWUIN stars, the question is whether such a star can have a wind at all. Testing this can be done similarly to how it was done by Krtička & Kubát (2014) for the case of winds with non-solar CNO abundances. Although this test is computationally expensive and goes beyond the scope of this work, here we summarize the basic idea, as well as the results we may expect from such a test, as a motivation for future work.…”

Section: Future Research On Twuin Stars -Theorymentioning

confidence: 99%

Low-metallicity massive single stars with rotation

Kubátová

Szécsi

Sander

et al. 2019

A&A

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Context. Metal-poor massive stars are assumed to be progenitors of certain supernovae, gamma-ray bursts, and compact object mergers that might contribute to the early epochs of the Universe with their strong ionizing radiation. However, this assumption remains mainly theoretical because individual spectroscopic observations of such objects have rarely been carried out below the metallicity of the Small Magellanic Cloud. Aims. Here we explore the predictions of the state-of-the-art theories of stellar evolution combined with those of stellar atmospheres about a certain type of metal-poor (0.02 Z⊙) hot massive stars, the chemically homogeneously evolving stars that we call Transparent Wind Ultraviolet INtense (TWUIN) stars. Methods. We computed synthetic spectra corresponding to a broad range in masses (20−130 M⊙) and covering several evolutionary phases from the zero-age main-sequence up to the core helium-burning stage. We investigated the influence of mass loss and wind clumping on spectral appearance and classified the spectra according to the Morgan-Keenan (MK) system. Results. We find that TWUIN stars show almost no emission lines during most of their core hydrogen-burning lifetimes. Most metal lines are completely absent, including nitrogen. During their core helium-burning stage, lines switch to emission, and even some metal lines (oxygen and carbon, but still almost no nitrogen) are detected. Mass loss and clumping play a significant role in line formation in later evolutionary phases, particularly during core helium-burning. Most of our spectra are classified as an early-O type giant or supergiant, and we find Wolf–Rayet stars of type WO in the core helium-burning phase. Conclusions. An extremely hot, early-O type star observed in a low-metallicity galaxy could be the result of chemically homogeneous evolution and might therefore be the progenitor of a long-duration gamma-ray burst or a type Ic supernova. TWUIN stars may play an important role in reionizing the Universe because they are hot without showing prominent emission lines during most of their lifetime.

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“…At solarlike metallicity, iron, with many optically thick lines in the wind, is the main driver of mass loss. At poorer metallicities the iron lines become optically thin while the strong resonance lines of CNO remain optically thick and may drive the wind (Vink et al 2001;Krtička & Kubát 2014). Krtička & Kubát (2014) establish the separation of these two regimes at Z 0.1 Z .…”

Section: Discussionmentioning

confidence: 80%

“…At poorer metallicities the iron lines become optically thin while the strong resonance lines of CNO remain optically thick and may drive the wind (Vink et al 2001;Krtička & Kubát 2014). Krtička & Kubát (2014) establish the separation of these two regimes at Z 0.1 Z . In other words: at the metallicity of IC1613, NGC3109 and WLṀ M and v ∞ (hence D mom ) depend not only on the stellar luminosity and global metallicity, but also on detailed abundances.…”

Section: Discussionmentioning

confidence: 80%

Winds of metal-poor OB stars: Updates from HST-COS UV spectroscopy

et al. 2014

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In the race to break the SMC frontier and reach metallicity conditions closer to the First Stars the information from UV spectroscopy is usually overlooked. New HST-COS observations of OB stars in the metal-poor galaxy IC1613, with oxygen content ~1/10 solar, have proved the important role of UV spectroscopy to characterize blue massive stars and their winds. The terminal velocities (υ∞) and abundances derived from the dataset have shed new light on the problem of metal-poor massive stars with strong winds. Furthermore, our results question the υ∞-υesc and υ∞-Z scaling relations whose use in optical-only studies may introduce large uncertainties in the derived mass loss rates and wind-momenta. Finally, our results indicate that the detailed abundance pattern of each star may have a non-negligible impact on its wind properties, and scaling these as a function of one single metallicity parameter is probably too coarse an approximation. Considering, for instance, that the [α/Fe] ratio evolves with the star formation history of each galaxy, we may be in need of updating all our wind recipes.

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Effect of rotational mixing and metallicity on the hot star wind mass-loss rates

Cited by 9 publications

References 31 publications

Comoving frame models of hot star winds

Comoving frame models of hot star winds

Low-metallicity massive single stars with rotation

Winds of metal-poor OB stars: Updates from HST-COS UV spectroscopy

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