Quantitative<i>H</i>and<i>K</i>band spectroscopy of Galactic OB-stars at medium resolution

Repolust, T.; Puls, J.; Hanson, M. M.; Kudritzki, Rolf‐Peter; Mokiem, M.R.

doi:10.1051/0004-6361:20052739

Cited by 67 publications

(97 citation statements)

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“…Here D(0.1) indicates that D is for the He/H = 0.1 abundance ratio. In this table we see that on average δD < 0 and that |δD| is larger the higher the He/H abundance ratio and for 19 000 < ∼ T eff < ∼ 23 000 K. In recent studies of supergiants Repolust et al (2005), Crowther et al (2006), Searle et al (2008), and Markova & Puls (2008) have found that an abundance He/H = 0.2 fits their atmospheres. From Table 9 we see that a ratio He/H = 0.2 effects the value of D by less than the error of measurement of D. Nevertheless, these differences are systematic and can be important for the hottest supergiants.…”

Section: Effects Related To the Rotationmentioning

confidence: 73%

Fundamental parameters of B supergiants from the BCD system

Zorec¹,

Cidale

Arias

et al. 2009

A&A

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Context. Effective temperatures of early-type supergiants are important to test stellar atmosphere-and internal structure-models of massive and intermediate mass objects at different evolutionary phases. However, these T eff values are more or less discrepant depending on the method used to determine them. Aims. We aim to obtain a new calibration of the T eff parameter for early-type supergiants as a function of observational quantities that are: a) highly sensitive to the ionization balance in the photosphere and its gas pressure; b) independent of the interstellar extinction; c) as much as possible model-independent. Methods. The observational quantities that best address our aims are the (λ 1 , D) parameters of the BCD spectrophotometric system. They describe the energy distribution around the Balmer discontinuity, which is highly sensitive to T eff and log g. We perform a calibration of the (λ 1 , D) parameters into T eff using effective temperatures derived with the bolometric-flux method for 217 program stars, whose individual uncertainties are on average |ΔT eff |/T f eff = 0.05. Results. We obtain a new and homogeneous calibration of the BCD (λ 1 , D) parameters for OB supergiants and revisit the current calibration of the (λ 1 , D) zone occupied by dwarfs and giants. The final comparison of calculated with obtained T eff values in the (λ 1 , D) calibration show that the latter have total uncertainties, which on average are T eff /T f eff ±0.05 for all spectral types and luminosity classes. Conclusions. The effective temperatures of OB supergiants derived in this work agree on average within some 2000 K with other determinations found in the literature, except those issued from wind-free non-LTE plane-parallel models of stellar atmospheres, which produce effective temperatures that can be overestimated by up to more than 5000 K near T eff = 25 000 K. Since the stellar spectra needed to obtain the (λ 1 , D) parameters are of low resolution, a calibration based on the BCD system is useful to study stars and stellar systems like open clusters, associations or stars in galaxies observed with multi-object spectrographs and/or spectro-imaging devices.

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Section: Effects Related To the Rotationmentioning

confidence: 73%

Fundamental parameters of B supergiants from the BCD system

Zorec¹,

Cidale

Arias

et al. 2009

A&A

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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%

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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“…At least for HD 190429A, an independent re-analysis by Bouret et al (2005), by means of the alternative model-atmosphere code cmfgen (Hillier & Miller 1998), confirms the corresponding calibration. Finally, for HD 15570, we use parameters derived from H-and K-band spectroscopy by Repolust et al (2005).…”

Section: Stellar Sample and Observational Materialsmentioning

confidence: 99%

Bright OB stars in the Galaxy

Puls¹,

Маркова²,

Scuderi³

et al. 2006

A&A

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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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QuantitativeHandKband spectroscopy of Galactic OB-stars at medium resolution

Cited by 67 publications

References 50 publications

Fundamental parameters of B supergiants from the BCD system

Fundamental parameters of B supergiants from the BCD system

Nitrogen line spectroscopy of O-stars

Bright OB stars in the Galaxy

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