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Shock-heated radiation-driven outflows as a solution to the weak-wind problem of late O-type stars
Solar and Stellar Astrophysics · Submitted 29 Mar 2021
abstract compiled · 2026-09-23 · no language-model review
The authors' main claim This offers a tentative basic explanation for the weak-wind problem: line-driven weak winds are not really weaker than theoretically expected, but rather a large portion of their wind volume is much hotter than the stellar effective temperature.
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Context. Radiation-driven mass loss is key to our understanding of massive-star evolution. However, for low-luminosity O-type stars there are big discrepancies between theoretically predicted and empirically derived mass-loss rates (called the weak-wind problem). Aims. We compute radiation-line-driven wind models of a typical weak-wind star to determine its temperature structure and the corresponding impact on ultra-violet (UV) line formation. Methods. We carried out hydrodynamic simulations of the line-deshadowing instability (LDI) for a weak-wind star in the Galaxy. Subsequently, we used this LDI model as input in a short-characteristics radiative transfer code to compute synthetic UV line profiles. Results. We find that the line-driven weak wind is significantly shock heated to high temperatures and is unable to cool down effciently. This results in a complex temperature structure where more than half of the wind volume has temperatures significantly higher than the stellar effective temperature. Therefore, a substantial portion of the weak wind will be more ionised, resulting in a reduction of the UV line opacity and therefore in weaker line profiles for a given mass-loss rate. Quantifying this, we find that weak-wind mass-loss rates derived from unsaturated UV lines could be underestimated by a factor of between 10 and 100 if the high-temperature gas is not properly taken into account in the spectroscopic analysis. This offers a tentative basic explanation for the weak-wind problem: line-driven weak winds are not really weaker than theoretically expected, but rather a large portion of their wind volume is much hotter than the stellar effective temperature.
background contribution method result interpretation main claim
| # | sentence | role | the authors' own work | states the main conclusion | strength |
|---|---|---|---|---|---|
| s0 | Context. | background 1.00 | 0.02 | 0.01 | unclear 1.00 |
| s1 | Radiation-driven mass loss is key to our understanding of massive-star evolution. | background 1.00 | 0.04 | 0.02 | asserted 1.00 |
| s2 | However, for low-luminosity O-type stars there are big discrepancies between theoretically predicted and empirically derived mass-loss rates (called the weak-wind problem). Aims. | background 0.54 | 0.05 | 0.02 | asserted 0.99 |
| s3 | We compute radiation-line-driven wind models of a typical weak-wind star to determine its temperature structure and the corresponding impact on ultra-violet (UV) line formation. Methods. | method 0.74 | 0.91 | 0.02 | asserted 0.68 |
| s4 | We carried out hydrodynamic simulations of the line-deshadowing instability (LDI) for a weak-wind star in the Galaxy. | method 0.99 | 0.96 | 0.02 | asserted 0.98 |
| s5 | Subsequently, we used this LDI model as input in a short-characteristics radiative transfer code to compute synthetic UV line profiles. Results. | method 0.99 | 0.95 | 0.02 | asserted 0.93 |
| s6 | We find that the line-driven weak wind is significantly shock heated to high temperatures and is unable to cool down effciently. | result 1.00 | 0.96 | 0.26 | asserted 1.00 |
| s7 | This results in a complex temperature structure where more than half of the wind volume has temperatures significantly higher than the stellar effective temperature. | result 1.00 | 0.92 | 0.11 | asserted 1.00 |
| s8 | Therefore, a substantial portion of the weak wind will be more ionised, resulting in a reduction of the UV line opacity and therefore in weaker line profiles for a given mass-loss rate. | interpretation 0.72 | 0.81 | 0.19 | asserted 0.99 |
| s9 | Quantifying this, we find that weak-wind mass-loss rates derived from unsaturated UV lines could be underestimated by a factor of between 10 and 100 if the high-temperature gas is not properly taken into account in the spectroscopic analysis. | result 0.99 | 0.96 | 0.30 | hedged possibility 0.54 |
| s10 | This offers a tentative basic explanation for the weak-wind problem: line-driven weak winds are not really weaker than theoretically expected, but rather a large portion of their wind volume is much hotter than the stellar effective temperature. | interpretation 1.00 | 0.64 | 0.92 | hedged possibility 0.93 |
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Original abstract
Context. Radiation-driven mass loss is key to our understanding of massive-star evolution. However, for low-luminosity O-type stars there are big discrepancies between theoretically predicted and empirically derived mass-loss rates (called the weak-wind problem). Aims. We compute radiation-line-driven wind models of a typical weak-wind star to determine its temperature structure and the corresponding impact on ultra-violet (UV) line formation. Methods. We carried out hydrodynamic simulations of the line-deshadowing instability (LDI) for a weak-wind star in the Galaxy. Subsequently, we used this LDI model as input in a short-characteristics radiative transfer code to compute synthetic UV line profiles. Results. We find that the line-driven weak wind is significantly shock heated to high temperatures and is unable to cool down effciently. This results in a complex temperature structure where more than half of the wind volume has temperatures significantly higher than the stellar effective temperature. Therefore, a substantial portion of the weak wind will be more ionised, resulting in a reduction of the UV line opacity and therefore in weaker line profiles for a given mass-loss rate. Quantifying this, we find that weak-wind mass-loss rates derived from unsaturated UV lines could be underestimated by a factor of between 10 and 100 if the high-temperature gas is not properly taken into account in the spectroscopic analysis. This offers a tentative basic explanation for the weak-wind problem: line-driven weak winds are not really weaker than theoretically expected, but rather a large portion of their wind volume is much hotter than the stellar effective temperature.
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This is two orders of magnitude higher than the wind mass loss rate reported by [ref] (weak wind problem, however, see also [ref] ).
Evolution of accretor stars in massive binaries: broader implications from modeling {\zeta} Ophiuchi · Surface rotation · 0.84
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