Line-driven Winds, Ionizing Fluxes, and Ultraviolet Spectra of Hot Stars at Extremely Low Metallicity. I. Very Massive O Stars

By R. Kudritzki. 2002

215 citations recorded by the source corpus.

Wind models of very massive stars with metallicities in a range from 10-4 to 1.0 solar are calculated using a new treatment of radiation-driven winds with depth-dependent radiative force multipliers and a comprehensive list of more than two million spectral lines in non-LTE (NLTE). The models are tested by a comparison with observed stellar wind properties of O stars in the Galaxy and the SMC. Satisfying agreement is found. The calculations yield mass-loss rates, wind velocities, wind momenta, and wind energies as functions of metallicity and can be used to discuss the influence of stellar winds on the evolution of very massive stars in the early universe and on the interstellar medium in the early phases of galaxy formation. It is shown that the normal scaling laws, which predict stellar mass-loss rates and wind momenta to decrease as a power law with metal abundance, break down at a certain threshold. Analytical fit formulae for mass-loss rates are provided as a function of stellar parameters and metallicity. Ionizing fluxes of hot stars depend crucially on the strengths of their stellar winds, which modify the absorption edges of hydrogen and helium (neutral and ionized) and the line blocking in the far-UV. The new wind models are therefore also applied to calculate ionizing fluxes and observable spectra of very massive stars as a function of metallicity using the new hydrodynamic, NLTE line-blanketed flux constant model atmosphere code developed by Pauldrach and coworkers. Numbers of ionizing photons for the crucial ionization stages are given. For a fixed effective temperature, the He II ionizing emergent flux depends very strongly on metallicity but also on stellar luminosity. A strong dependence on metallicity is also found for the C III, Ne II, and O II ionizing photons, whereas the H I and He I ionizing flux is almost independent of metallicity. We also calculate UV spectra for all the models and discuss the behavior of significant line features as a function of metallicity.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/70ee06993844afdbe060fc16543a18aa19f1fa74

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In Astronomy and Astrophysics

1. N. Smith
2. S. Smartt
3. Michela Mapelli
4. N. Langer
5. Stan Woosley
6. Mario Spera
7. N. Giacobbo
8. G. Meynet

Citations in the corpus

• EXTRAGALACTIC CHEMICAL ABUNDANCES: DO H ii REGIONS AND YOUNG STARS TELL THE SAME STORY? THE CASE OF THE SPIRAL GALAXY NGC 300 (2009, background): “Softer ionizing stellar continua with increasing metallicity are theoretically expected for hot stars, due to the enhanced metal line blocking (Kudritzki 2002; Mokiem et al. 2004).”
• NUCLEOSYNTHESIS AND EVOLUTION OF MASSIVE METAL-FREE STARS (2008, methodology): “Calculations by Kudritzki (2002) and Meynet & Maeder (2002), for example, suggest that the mass loss for non-rotating stars lighter than 100 M and metallicity 10−5 Z can be neglected, though see Meynet et al. (2006).”
• Effects of rotation on the evolution of primordial stars (2008, methodology): “However, according to Kudritzki (2002), H and He lines are able to remove some mass if the luminosity is sufficiently high.”
• THE ORIGIN AND OPTICAL DEPTH OF IONIZING RADIATION IN THE “GREEN PEA” GALAXIES (2013, methodology): “…of hot O stars needed to generate the observed He ii luminosities, we use the ionizing photon rates from Kudritzki (2002) for the log(L/L⊙) = 7.03, 60,000 K star (see Figure 11 of Kudritzki 2002) and emissivities and recombination rates for Te = 15, 000 K and nH = 100 cm −3 (Storey & Hummer 1995).”
• The evolution of runaway stellar collision products (2009, background): “Apart from the de Jager and Vink rates, we also considered the mass loss rate from Kudritzki (2002).”
• The mass spectrum of compact remnants from the parsec stellar evolution tracks (2015, methodology): “The rate of mass loss by stellar winds on the MS increases with the metallicity of the star as ˙ M ∝ Z α , where α ∼ 0.5–0.9, depending on the model (e.g. Ku-dritzki, Pauldrach & Puls 1987; Leitherer, Robert & Drissen 1992; Kudritzki & Puls 2000; Vink, de Koter & Lamers 2001; Kudritzki 2002).”
• Toward Understanding Massive Star Formation (2007, background): “As the linedriven wind mass loss from massive stars is metallicity-dependent (Kudritzki 2002) the upper mass limit would be metallicity-dependent, too.”
• The Formation of the First Stars. II. Radiative Feedback Processes and Implications for the Initial Mass Function (2007, background): “A potential simplification in assessing these effects is that massive primordial stars are thought to have much smaller mass-loss rates than contemporary massive stars (Kudritzki 2002), so that the mass at core collapse should be quite similar to the initial mass.”
• Wind modelling of very massive stars up to 300 solar masses (2011, background): “In reality, however, α is depth-dependent (Vink 2000, Kudritzki 2002, Gr¨afener & Hamann 2005, Muijres et al. 2011b), which is captured better by an alternative representation of the line acceleration (M¨uller & Vink 2008).”
• The VLT-FLAMES Survey of Massive Stars: Observations in the Galactic Clusters NGC 3293, NGC 4755 and NGC 6611 ⋆ (2005, background): “Indeed, one of the key challenges is to fully understand the role of metallicity on stellar evolution, to place better constraints on extremely low-metallicity stellar models (e.g. Kudritzki 2002).”
• Scaled solar tracks and isochrones in a large region of the Z-Y plane. II. From 2.5 to 20 solar masses (2009, methodology): “A relevant review on the evolution of massive stars with mass loss was given by Chiosi & Maeder (1986), while Kudritzki & Puls (2000) exhaustively describe winds from hot stars.”
• Massive Stars in the Local Group: Implications for Stellar Evolution and Star Formation (2003, background): “Kudritzki (2002) finds that A nn u.”
• Early Reionization by Miniquasars (2003, background): “Since, at zero metallicity, mass loss through radiativelydriven stellar winds or nuclear-powered stellar pulsations is expected to be negligible (Kudritzki 2002; Baraffe, Heger, & Woosley 2001), Population III stars will likely die losing only a small fraction of their mass. Nonrotating very…”
• The progenitors of core-collapse supernovae (2004, background): “Although the theoretical rates of Kudritzki (2002) indicate that a change in the mass-loss rates in this region is expected.”
• The Physical Properties and Effective Temperature Scale of O-Type Stars as a Function of Metallicity. II. Analysis of 20 More Magellanic Cloud Stars and Results from the Complete Sample (2005, methodology): “Kudritzki (2002) has performed careful calculations of the effects of metallicity and effective temperature on the force multipliers, and his calculations show that at an SMC-like metallicity that α will be 3% (Teff ≈ 40000 K) and 15% (Teff ≈ 50000 K) larger at an SMC-like metallicity than in the…”
• A LIBRARY OF THEORETICAL ULTRAVIOLET SPECTRA OF MASSIVE, HOT STARS FOR EVOLUTIONARY SYNTHESIS (2010, methodology): “We adopted their relation, together with updates and modifications by Kudritzki (2002) and Markova et al. (2004).”