Modeling the near-infrared lines of O-type stars

Lenorzer, A.; Mokiem, M.R.; Koter, A. de; Puls, J.

doi:10.1051/0004-6361:20047174

Cited by 45 publications

(89 citation statements)

References 49 publications

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“…For this purpose, we used a grid of models for dwarfs and supergiants in the O and early B-star range, which has already been used in previous comparisons (Lenorzer et al 2004;Puls et al 2005;Repolust et al 2005). fastwind models have been calculated with three "explicit" atoms, H, He and our new N atom.…”

Section: Comparison With Results From Cmfgenmentioning

confidence: 99%

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Nitrogen line spectroscopy of O-stars

González

Puls

Najarro

2011

A&A

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Context. Evolutionary models of massive stars predict a surface enrichment of nitrogen, due to rotational mixing. Recent studies within the VLT-FLAMES survey of massive stars have challenged (part of) these predictions. Such systematic determinations of nitrogen abundances, however, have been mostly performed only for cooler (B-type) objects. For the most massive and hottest stars, corresponding results are scarce. Aims. This is the first paper in a series dealing with optical nitrogen spectroscopy of O-type stars, aiming at the analysis of nitrogen abundances for stellar samples of significant size, to place further constraints on the early evolution of massive stars. Here we concentrate on the formation of the optical N iii lines at λλ4634−4640−4642 that are fundamental for the definition of the different morphological "f"-classes. Methods. We implement a new nitrogen model atom into the NLTE atmosphere/spectrum synthesis code fastwind, and compare the resulting optical Niii spectra with other predictions, mostly from the seminal work by Mihalas & Hummer (1973, ApJ, 179, 827, "MH"), and from the alternative code cmfgen.Results. Using similar model atmospheres as MH (not blanketed and wind-free), we are able to reproduce their results, in particular the optical triplet emission lines. According to MH, these should be strongly related to dielectronic recombination and the drain by certain two-electron transitions. However, using realistic, fully line-blanketed atmospheres at solar abundances, the key role of the dielectronic recombinations controlling these emission features is superseded -for O-star conditions -by the strength of the stellar wind and metallicity. Thus, in the case of wind-free (weak wind) models, the resulting lower ionizing EUV-fluxes severely suppress the emission. As the mass loss rate is increased, pumping through the N iii resonance line(s) in the presence of a near-photospheric velocity field (i.e., the Swings-mechanism) results in a net optical triplet line emission. A comparison with results from cmfgen is mostly satisfactory, except for the range 30 000 K ≤ T eff ≤ 35 000 K, where cmfgen triggers the triplet emission at lower T eff than fastwind. This effect could be traced down to line overlap effects between the N iii and O iii resonance lines that cannot be simulated by fastwind so far, due to the lack of a detailed O iii model atom. Conclusions. Since the efficiency of dielectronic recombination and "two electron drain" strongly depends on the degree of lineblanketing/-blocking, we predict the emission to become stronger in a metal-poor environment, though lower wind-strengths and nitrogen abundances might counteract this effect. Weak winded stars (if existent in the decisive parameter range) should display less triplet emission than their counterparts with "normal" winds.

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Section: Comparison With Results From Cmfgenmentioning

confidence: 99%

“…Table 4 lists important N iii lines in the range between 4000 to 6500 Å, together with multiplet numbers according to Moore (1975), to provide Notes. The grid is a subset of the grid presented by Lenorzer et al (2004).…”

Section: Comparison With Results From Cmfgenmentioning

confidence: 99%

Nitrogen line spectroscopy of O-stars

González

Puls

Najarro

2011

A&A

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“…As shown in Figure 6 (top right), the optical appearance is of an extensive ionized region overlaid with a dense foreground dust lane; the visual extinction toward the deeply embedded object IRS 2 (Grasdalen 1974) has recently been determined as !27 mag at 2.2 m (Lenorzer et al 2004). Although IRS 2 contributes significantly to the ionization, it was known for some time that this star did not meet the O9-O9.5 stellar equivalent required.…”

Section: Ngc 2024mentioning

confidence: 95%

Large Area Mapping at 850 μm. IV. Analysis of the Clump Distribution in the Orion B South Molecular Cloud

Johnstone

Matthews

Mitchell

2006

ApJ

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We present results from a survey of a 1300 arcmin 2 region of the Orion B South molecular cloud, including NGC 2024, NGC 2023, and the Horsehead Nebula ( B33), obtained using the Submillimetre Common-User Bolometer Array (SCUBA) on the James Clerk Maxwell Telescope (JCMT). Submillimeter continuum observations at 450 and 850 m are discussed. Using an automated algorithm, 57 discrete emission features (''clumps'') are identified in the 850 m map. The physical conditions within these clumps are investigated under the assumption that the objects are in quasi-hydrostatic equilibrium. The best-fit dust temperature for the clumps is found to be T d ¼ 18 AE 4 K, with the exception of those associated with the few known far-infrared sources residing in NGC 2024. The latter internally heated sources are found to be much warmer. In the region surrounding NGC 2023, the clump dust temperatures agree with clump gas temperatures determined from molecular line excitation measurements of the CO molecule. The bounding pressure on the clumps lies in the range log (k À1 P cm 3 K À1 ) ¼ 6:1 AE 0:3. The cumulative mass distribution is steep at the high-mass end, as is the stellar initial mass function. The distribution flattens significantly at lower masses, with a turnover around 3-10 M .

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“….16, at least if there have been no major changes in the average wind properties between their UV and our radio observations. Additionally, Bouret et al (2005) point to the fact that the predictions by Lenorzer et al (2004) concerning Br α indicate that the outer winds "would be less affected by clumping", compared to the regions they could access. Thus far, the situation remains unclear.…”

Section: Implications and Conclusionmentioning

confidence: 99%

Bright OB stars in the Galaxy

Puls¹,

Маркова²,

Scuderi³

et al. 2006

A&A

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291

391

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Context. Recent results strongly challenge the canonical picture of massive star winds: various evidence indicates that currently accepted mass-loss rates,Ṁ, may need to be revised downwards, by factors extending to one magnitude or even more. This is because the most commonly used mass-loss diagnostics are affected by "clumping" (small-scale density inhomogeneities), influencing our interpretation of observed spectra and fluxes. Aims. Such downward revisions would have dramatic consequences for the evolution of, and feedback from, massive stars, and thus robust determinations of the clumping properties and mass-loss rates are urgently needed. We present a first attempt concerning this objective, by means of constraining the radial stratification of the so-called clumping factor. Methods. To this end, we have analyzed a sample of 19 Galactic O-type supergiants/giants, by combining our own and archival data for H α , IR, mm and radio fluxes, and using approximate methods, calibrated to more sophisticated models. Clumping has been included into our analysis in the "conventional" way, by assuming the inter-clump matter to be void. Because (almost) all our diagnostics depends on the square of density, we cannot derive absolute clumping factors, but only factors normalized to a certain minimum. Results. This minimum was usually found to be located in the outermost, radio-emitting region, i.e., the radio mass-loss rates are the lowest ones, compared toṀ derived from H α and the IR. The radio rates agree well with those predicted by theory, but are only upper limits, due to unknown clumping in the outer wind. H α turned out to be a useful tool to derive the clumping properties inside r < 3. . .5 R . Our most important result concerns a (physical) difference between denser and thinner winds: for denser winds, the innermost region is more strongly clumped than the outermost one (with a normalized clumping factor of 4.1 ± 1.4), whereas thinner winds have similar clumping properties in the inner and outer regions. Conclusions. Our findings are compared with theoretical predictions, and the implications are discussed in detail, by assuming different scenarios regarding the still unknown clumping properties of the outer wind.

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Modeling the near-infrared lines of O-type stars

Cited by 45 publications

References 49 publications

Nitrogen line spectroscopy of O-stars

Nitrogen line spectroscopy of O-stars

Large Area Mapping at 850 μm. IV. Analysis of the Clump Distribution in the Orion B South Molecular Cloud

Bright OB stars in the Galaxy

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