Puzzling wind properties of young massive stars in SMC-N81

Martins, F.; Hillier, D. J.; Heydari-Malayeri, M.

doi:10.1051/0004-6361:20034509

Cited by 83 publications

(127 citation statements)

References 61 publications

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“…The calculations of Aerts et al (2004) match the observed mass-loss rates for Car, which has a peak of 1:6 AE 0:3 ð Þ; 10 À3 M yr À1 (assuming spherical symmetry) during normal outbursts, falling to 10 À5 M yr À1 during the intervening 5.5 yr (van Boekel et al 2003). For young (P4 Myr) O stars in the small Magellanic cloud, low (P10 À8 M yr À1 ) mass-loss rates were observed ( Martins et al 2004), indicating that massive stars may have much lower mass-loss rates until they approach the end of their main-sequence lifetimes (see Meynet & Maeder 2003).…”

Section: Evolution Of the Merger Productsupporting

confidence: 65%

The Ecology of Star Clusters and Intermediate‐Mass Black Holes in the Galactic Bulge

Zwart

Baumgardt

McMillan

et al. 2006

ApJ

133

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We simulate the inner 100 pc of the Milky Way to study the formation and evolution of the population of star clusters and intermediate-mass black holes ( IMBHs). For this study we perform extensive direct N-body simulations of the star clusters that reside in the bulge, and of the inner few tenth of parsecs of the supermassive black hole in the Galactic center. In our N-body simulations the dynamical friction of the star cluster in the tidal field of the bulge are taken into account via semianalytic solutions. The N-body calculations are used to calibrate a semianalytic model of the formation and evolution of the bulge. We find that $10% of the clusters born within $100 pc of the Galactic center undergo core collapse during their inward migration and form IMBHs via runaway stellar merging. After the clusters dissolve, these IMBHs continue their inward drift, carrying a few of the most massive stars with them. We predict that a region within $10 pc of the supermassive black hole (SMBH) is populated by $50 IMBHs of $1000 M . Several of these are still expected to be accompanied by some of the most massive stars from the star cluster. We also find that within a few milliparsecs of the SMBH there is a steady population of several IMBHs. This population drives the merger rate between IMBHs and the SMBH at a rate of about one per 10 Myr, sufficient to build the accumulated majority of mass of the SMBH. Mergers of IMBHs with SMBHs throughout the universe are detectable by LISA at a rate of about two per week.

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Section: Evolution Of the Merger Productsupporting

confidence: 65%

The Ecology of Star Clusters and Intermediate‐Mass Black Holes in the Galactic Bulge

Zwart

Baumgardt

McMillan

et al. 2006

ApJ

133

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“…At the moment, the nature of this weak-wind problem eludes us; for a discussion we refer to e.g. Martins et al (2004), Martins et al (2005), de Koter (2006), Table 2. Adopted model parameters together with predicted mass loss rates for two clumping stratifications and porosity descriptions.…”

Section: The Weak-wind Problemmentioning

confidence: 99%

Predictions of the effect of clumping on the wind properties of O-type stars

Muijres

Koter

Vink

et al. 2010

A&A

100

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Aims. Both empirical evidence and theoretical findings indicate that the stellar winds of massive early-type stars are inhomogeneous, i.e., porous and clumpy. For relatively dense winds, empirically derived mass-loss rates might be reconciled with predictions if these empirical rates are corrected for clumping. The predictions, however, do not account for structure in the wind. To allow for a consistent comparison, we investigate and quantify the effect of clumpiness and porosity of the outflow on the predicted wind energy and the maximal effect on the mass-loss rate of O-type stars. Methods. Combining non-LTE model atmospheres and a Monte Carlo method to compute the transfer of momentum from the photons to the gas, the effect of clumping and porosity on the energy transferred from the radiation field to the wind is computed in outflows in which the clumping and porosity stratification is parameterized by heuristic prescriptions. Results. The impact of structure in the outflow on the wind energy is complex and is a function of stellar temperature, the density of gas in the clumps, and the physical scale of the clumps. If the medium is already clumped in the photosphere, the emergent radiation field will be softer, slightly increasing the wind energy of relatively cool O stars (30 000 K) but slightly decreasing it for relatively hot O stars (40 000 K). More important is that as a result of recombination of the gas in a clumped wind the line force increases. However, because of porosity the line force decreases, simply because photons may travel in-between the clumps, avoiding interactions with the gas. If the changes in the wind energy only affect the mass-loss rate and not the terminal velocity of the flow, we find that the combined effect of clumpiness and porosity is a small reduction in the mass-loss rate if the clumps are smaller than 1/100th the local density scale height H ρ . In this case, empirical mass-loss determinations based on Hα fitting and theory match for stars with dense winds (Ṁ > ∼ 10 −7 M yr −1 ) if the overdensity of gas in the clumps, relative to the case of a smooth wind, is modest. For clumps larger than 1/10th H ρ , the predicted mass-loss rates exhibit almost the same dependence on clumpiness as do empirical rates. We show that this implies that empirical and predicted mass-loss rates can no longer be matched. Very high overdensities of gas in clumps of such large size may cause the predictedṀ to decrease by a factor of from 10 to 100. This type of structure is likely not to be the cause of the "weak-wind problem" in early-type stars, unless a mechanism can be identified that causes extreme structure to develop in winds for whichṀ < ∼ 10 −7 M yr −1 (weak winds) that is not active in denser winds.

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“…Observational studies consider the turbulence already present in the photospheres of O stars (e.g., Bouret et al 2003Bouret et al , 2005Martins et al 2004Martins et al , 2005 with turbulent velocities of about 2−25 km s −1 . Macroturbulent velocities in B supergiants may be even higher, about 30−100 km s −1 (Howarth et al 1997;Markova & Puls 2008).…”

Section: Models With Base Turbulencementioning

confidence: 99%

“…On the other hand, the modified ionization equilibrium may affect the X-ray line formation (Oskinova et al 2006;Krtička & Kubát 2009), and too ling cooling time in the post-shock region (Cohen et al 2008;Krtička & Kubát 2009) may cause the so-called "weak wind problem" (Bouret et al 2003;Martins et al 2004;Marcolino et al 2009). …”

Section: Introductionmentioning

confidence: 99%

Comoving frame models of hot star winds

Krtička¹,

Kubát

2010

A&A

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We provide hot star wind models with radiative force calculated using the solution of comoving frame (CMF) radiative transfer equation. The wind models are calculated for the first stars, O stars, and the central stars of planetary nebulae. We show that without line overlaps and with solely thermal line broadening the pure Sobolev approximation provides a reliable estimate of the radiative force even close to the wind sonic point. Consequently, models with the Sobolev line force provide good approximations to solutions obtained with non-Sobolev transfer. Taking line overlaps into account, the radiative force becomes slightly lower, leading to a decrease in the wind mass-loss rate by roughly 40%. Below the sonic point, the CMF line force is significantly lower than the Sobolev one. In the case of pure thermal broadening, this does not influence the mass-loss rate, as the wind mass-loss rate is set in the supersonic part of the wind. However, when additional line broadening is present (e.g., the turbulent one) the region of low CMF line force may extend outwards to the regions where the mass-loss rate is set. This results in a decrease in the wind mass-loss rate. This effect can at least partly explain the low wind mass-loss rates derived from some observational analyses of luminous O stars.

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Puzzling wind properties of young massive stars in SMC-N81

Cited by 83 publications

References 61 publications

The Ecology of Star Clusters and Intermediate‐Mass Black Holes in the Galactic Bulge

The Ecology of Star Clusters and Intermediate‐Mass Black Holes in the Galactic Bulge

Predictions of the effect of clumping on the wind properties of O-type stars

Comoving frame models of hot star winds

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