EDP Sciences
Free Access
Issue
A&A
Volume 583, November 2015
Article Number A63
Number of page(s) 35
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361/201424976
Published online 29 October 2015

Online material

Appendix A: Figures and model data

thumbnail Fig. A.1

Computed spectra and corresponding continua (Eddington flux Hν in erg/cm2/ s/Hz versus the photon energy in Rydberg) for the dwarf models at Teff = 30 000 K (left column), Teff = 35 000 K (middle column), and Teff = 40 000 K (right column) and different metallicities (0.1, 0.4, 1.0, and 2.0 times the solar metallicity from top to bottom). The data can be copied from Weber et al. (2015)23.

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thumbnail Fig. A.2

Same as Fig. A.1 but for Teff = 45 000 K, Teff = 50 000 K, and Teff = 55 000 K.

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thumbnail Fig. A.3

Same as Fig. A.1 but for supergiant models with Teff = 30 000 K, Teff = 35 000 K, and Teff = 40 000 K.

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thumbnail Fig. A.4

Same as Fig. A.1 but for supergiant models with Teff = 45 000 K and Teff = 50 000 K.

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thumbnail Fig. A.5

Same as Fig. A.1 but for VMS models in the mass range between 150 M and 600 M.

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thumbnail Fig. A.6

Same as Fig. A.1 but for VMS models in the mass range between 1000 M and 3000 M.

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thumbnail Fig. A.7

Ionization structures of hydrogen, helium, oxygen, and sulfur of H ii regions around dwarf stars of effective temperatures of 30 000 K, 40 000 K, and 50 000 K at different metallicities (a homogeneous gas with a hydrogen particle density of 10 cm-3 and the same chemical composition as the central star is assumed). Because the number of hydrogen-ionizing photons varies only slightly for stars with the same effective temperature and luminosity class (Table 4), the larger hydrogen Strömgren radii obtained for lower metallicities are primarily caused by the larger temperatures of the gas, which in turn are caused mainly by the direct influence of the lower metallicities of the gas (see Fig. A.9).

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thumbnail Fig. A.8

Same as Fig. A.7, but using supergiants as ionizing sources.

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thumbnail Fig. A.9

Temperature structures of H ii regions around dwarf stars and supergiants of effective temperatures of 30 000 K, 40 000 K, and 50 000 K at different metallicities (using the same physical conditions for the gas as in Fig. A.7). The influence of the metallicity on the temperature of the gas is primarily a result of the reduced number of metal particles that contribute to the cooling of the gas (metal-poorer H ii regions are thus characterized by considerably higher temperatures than H ii regions with larger metal abundances), but it is also a result of the harder ionization spectra obtained for metal-poorer stars (see Figs. A.1A.4), which results in a larger energy input by photoionization heating; the temperature of the gas therefore rises with decreasing metallicity of the irradiating stars (see also Fig. A.10).

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thumbnail Fig. A.10

Comparison of the ionization structures of H, He, O, and S, and the temperature structure of H ii regions for cases where the chemical composition of the gas is not the same as that of the irradiating star (for the gas a hydrogen particle density of 10 cm-3 and solar metallicity is assumed, whereas for the stars a 40 000 K dwarf model with metallicity from 0.1 Z to 2.0 Z is used). In this way the influence of the metallicity-dependent ionizing spectra on the physical behavior of the gas can be investigated independently of the influence of the metallicity of the gas. As the stellar spectra differ for different metallicities especially in the energy range above the ionization edge of He i, the differences obtained for the ionization structures of O and S are more pronounced than those of H and He. These differences lead to enhanced ionization fractions of O ii and S iii for the spectra of low-metallicity stars, because the spectra of these stars are “harder” than those of high-metallicity stars of the same effective temperature (see Figs. A.1A.4). As a consequence of this behavior the temperature of the gas also increases, but this effect is smaller than in the case where the metallicity of the gas is the same as that of the star (Fig. A.9).

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thumbnail Fig. A.11

Synthetic images showing the intensities of important emission lines from various ionization stages of oxygen around very massive stars with metallicities of 0.05 Z and 1.0 Z. Lower metallicity means lower densities of the metal ions in the gas, but the corresponding reduction of the optical emission lines is partly compensated by the higher temperatures and the resulting higher rate coefficients for collisional excitation. The values are shown using a logarithmic color scale because the emission line strengths vary strongly between the different models.

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© ESO, 2015

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