The Discordance of Mass‐Loss Estimates for Galactic O‐Type Stars

Fullerton, A. W.; Massa, Derck; Prinja, R. K.

doi:10.1086/498560

Cited by 348 publications

(463 citation statements)

References 68 publications

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“…Since Vink et al predict an increase inṀ of a factor of five, this would imply that the clumping factors for hotter objects are larger by factors of 4 (most optimistic case) to 156 (worst case) compared to those of cooler ones 20 . Given our present knowledge (see Fullerton et al 2006;Puls et al 2006, and references therein), this is not impossible, but raises the question about the physical origin of such a difference. This hypothesis would also imply that all B-SG mass-loss rates are overpredicted, though to a lesser extent for cooler subtypes.…”

Section: Discussionmentioning

confidence: 98%

“…However, recent observational studies of clumping in O-SGs have revealed inconsistencies both between results originating from different wind diagnostics, such as UV resonance lines, H α and the IR-/radioexcess (Fullerton et al 2006;Puls et al 2006), and between theoretical predictions and observed constraints on the radial stratification of the clumping factor (Bouret et al 2005;Puls et al 2006). In addition, there are observational results which imply that clumping might depend on wind density.…”

Section: Introductionmentioning

confidence: 99%

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Bright OB stars in the Galaxy

Маркова¹,

Puls²

2007

A&A

189

264

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Context. B-type supergiants represent an important phase in the evolution of massive stars. Reliable estimates of their stellar and wind parameters, however, are scarce, especially at mid and late spectral subtypes. Aims. We apply the NLTE atmosphere code FASTWIND to perform a spectroscopic study of a small sample of Galactic B-supergiants from B0 to B9. By means of the resulting data and incorporating additional datasets from alternative studies, we investigate the properties of OB-supergiants and compare our findings with theoretical predictions. Methods. Stellar and wind parameters of our sample stars are determined by line profile fitting, based on synthetic profiles, a Fourier technique to investigate the individual contributions of stellar rotation and "macro-turbulence" and an adequate approach to determine the Si abundances in parallel with micro-turbulent velocities. Results. Due to the combined effects of line-and wind-blanketing, the temperature scale of Galactic B-supergiants needs to be revised downward, by 10 to 20%, the latter value being appropriate for stronger winds. Compared to theoretical predictions, the wind properties of OB-supergiants indicate a number of discrepancies. In fair accordance with recent results, our sample indicates a gradual decrease in v ∞ over the bi-stability region, where the limits of this region are located at lower T eff than those predicted. Introducing a distance-independent quantity Q related to wind-strength, we show that this quantity is a well defined, monotonically increasing function of T eff outside this region. Inside and from hot to cool,Ṁ changes by a factor (in between 0.4 and 2.5) which is much smaller than the predicted factor of 5. Conclusions. The decrease in v ∞ over the bi-stability region is not over-compensated by an increase ofṀ , as frequently argued, provided that wind-clumping properties on both sides of this region do not differ substantially.

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Section: Discussionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

Bright OB stars in the Galaxy

Маркова¹,

Puls²

2007

A&A

189

264

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“…We next consider whether the observed variability in the absorbing column could be due to wind structures, and how the characteristics of those structures compare to what is known about radiatively driven winds in other contexts, such as clumps (Abbott et al 1981;Hillier & Miller 1998;Fullerton et al 2006;Puls et al 2006) or discrete absorption components (DACs; Prinja & Howarth 1986). To this end, we use a numerical code to simulate the column density between the observer and a point-like X-ray source, as the source orbits around a companion whose wind is composed of discrete clumps.…”

Section: Clumpy Wind Model For the Hard Statementioning

confidence: 99%

Long term variability of Cygnus X-1

Grinberg

Leutenegger

Hell

et al. 2015

A&A

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Binary systems with an accreting compact object offer a unique opportunity to investigate the strong, clumpy, line-driven winds of early-type supergiants by using the compact object's X-rays to probe the wind structure. We analyze the two-component wind of HDE 226868, the O9.7Iab giant companion of the black hole Cyg X-1, using 4.77 Ms Rossi X-ray Timing Explorer (RXTE) observations of the system taken over the course of 16 years. Absorption changes strongly over the 5.6 d binary orbit, but also shows a large scatter at a given orbital phase, especially at superior conjunction. The orbital variability is most prominent when the black hole is in the hard X-ray state. Our data are poorer for the intermediate and soft state, but show signs for orbital variability of the absorption column in the intermediate state. We quantitatively compare the data in the hard state to a toy model of a focussed Castor-AbbottKlein wind: as it does not incorporate clumping, the model does not describe the observations well. A qualitative comparison to a simplified simulation of clumpy winds with spherical clumps shows good agreement in the distribution of the equivalent hydrogen column density for models with a porosity length on the order of the stellar radius at inferior conjunction; we conjecture that the deviations between data and model at superior conjunction could either be due to lack of a focussed wind component in the model or to a more complicated clump structure.

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“…For the resonance lines P v λλ1118, 1128, N v λλ1239, 1243, Si iv λλ1394, 1403, and C iv λλ1548, 1551, it is well known that the crucial parameter needed to fit the profiles is the line optical depth which is directly proportional to the mass-loss rate and the respective ionization fraction (see for instance the case of P v λλ1118, 1128 in Fullerton et al 2006). …”

Section: Winds Highly Ionized By X-raysmentioning

confidence: 99%

Analysis of Galactic late-type O dwarfs: more constraints on the weak wind problem

Marcolino

Bouret

Martins

et al. 2009

A&A

123

169

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Aims. We investigate the stellar and wind properties of a sample of late-type O dwarfs. Previous analyses of such stars have found very low mass-loss rates; rates much lower than predicted by theory (the weak wind problem). Methods. Far-UV to optical spectra of five Galactic O stars were analyzed: HD 216898 (O9IV/O8.5V), HD 326329 (O9V), HD 66788 (O8V/O9V), ζ Oph (O9.5Vnn), and HD 216532 (O8.5V((n))). We used a grid of TLUSTY models to obtain effective temperatures, gravities, rotational velocities, and to identify wind lines. Wind parameters for each object were obtained using expanding atmosphere models calculated with the CMFGEN code.Results. The spectra of our sample have primarily a photospheric origin. A weak wind signature is seen in C iv λλ1548, 1551, from which mass-loss rates consistent with previous CMFGEN results for O8-O9V stars were derived (∼10 −10 −10 −9 M yr −1 ). A discrepancy of roughly two orders of magnitude is found between these mass-loss rates and the values predicted by theory (Ṁ Vink ), confirming a breakdown or a steepening of the modified wind momentum-luminosity relation at log L /L < ∼ 5.2. We have estimated the carbon abundance for the stars of our sample and concluded that its value cannot be reduced to sufficiently small values to solve the weak wind problem. Upper limits onṀ were established for all objects using lines of different ions: P v λλ1118, 1128, C iii λ1176, N v λλ1239, 1243, Si iv λλ1394, 1403, and N iv λ1718. All the values obtained are in disagreement with theoretical predictions, bringing support to the reality of weak winds. Together with C iv λλ1548, 1551, the use of N v λλ1239, 1243 results in the lowest mass-loss rates: the upper limits indicate thatṀ must be less than about −1.0 dexṀ Vink . Upper mass-loss rate limits obtained for other transitions are also low: they indicate thatṀ must be less than about (−0.5 ± 0.2) dexṀ Vink . We studied the behavior of the Hα line with different mass-loss rates. For two stars, only models with very lowṀ's provide the best fit to the UV and optical spectra. We also explored ways to fit the observed spectra with the theoretical mass-loss rates. By using large amounts of X-rays, we could reduce the predicted wind emission to the observed levels. However, unrealistic X-ray luminosities had to be used (log L X /L Bol > ∼ −3.5). The validity of the models used in our analyses is discussed.

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The Discordance of Mass‐Loss Estimates for Galactic O‐Type Stars

Cited by 348 publications

References 68 publications

Bright OB stars in the Galaxy

Bright OB stars in the Galaxy

Long term variability of Cygnus X-1

Analysis of Galactic late-type O dwarfs: more constraints on the weak wind problem

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