Letters of Intent received in 2016

LoI 2018-1888
Focus Meeting: [The X-ray view of stellar winds]

Date: 20 August 2018 to 31 August 2018
Category: Focus meetings (GA)
Location: Vienna, Austria
Contact: Gregor Rauw (rauw@astro.ulg.ac.be)
Coordinating division: Division G Stars and Stellar Physics
Other divisions: Division D High Energy Phenomena and Fundamental Physics
Division H Interstellar Matter and Local Universe
Chair of SOC: Gregor Rauw (Liège University)
Chair of LOC: ()

 

Topics

- X-ray emission from stellar winds throughout the Hertzsprung-Russell diagram (classical massive stars, sdOs, CSPNe, gamma-Cas stars, ApBp stars,...)
- Structures in stellar outflows (both small and large-scale structures, direct emission, absorption signatures in HMXBs,...)
- Interacting winds (colliding wind binaries, PNe, wind-blown bubbles and superbubbles, bow shocks,...)
[For further details see the Rationale section]

 

Rationale

Focus Meeting: The X-ray view of stellar winds
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Rationale:
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Mass loss through supersonic stellar winds affects most types of stars over at least some parts of their evolution. These outflows impact the evolution of the stars and constitute a key source of chemical and dynamical feedback for the interstellar medium. The highly energetic interactions of stellar winds with the surrounding interstellar material or with the wind of a companion star in binary systems not only produce spectacular phenomena such as bubbles or colliding winds, but they also contribute to the acceleration of relativistic particles.
The X-ray domain has an enormous diagnostic potential to investigate the hydrodynamics of stellar winds: owing to the huge wind velocities, shocks and magnetic interactions in stellar winds produce the strongest observational signatures in the X-ray domain. The current generation of X-ray satellites led to tremendous progress in our understanding of the physics of stellar outflows in all kinds of stars, from classical massive stars to low-mass hot subdwarfs, enigmatic γ Cassiopeia stars and low-mass stars. Further progress is expected with the innovative high-spectral resolution instrumentations that are currently being designed for future X-ray observatories (Athena, Arcus, AstroH2).
Time is ripe to gather people from the different communities concerned by these questions, to discuss the results obtained with current facilities, to highlight open issues, and to clearly define our needs in order to make the best possible use of the future facilities. For this purpose, we propose to organize a two days Focus Meeting at the 2018 IAU General Assembly in Vienna. For the same GA, there is also a proposal to hold an IAU Symposium on “High-mass X-ray binaries at the cross-roads of astrophysics” which will be fully complementary to the event proposed here. Given the strong overlap between the communities interested in both events, we suggest to organize the present FM either immediately before or immediately after the Symposium on HMXBs.

Main Topics to be discussed during this event :
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- X-rays emission from stellar winds throughout the Hertzsprung-Russell diagram
Stellar outflows are ubiquitous although the dominant driving mechanisms differ between cool stars (pressure driven coronal winds) and hot stars (line-driven winds). The observational signatures that these winds produce in the X-ray domain allow us to efficiently probe their physics. Bringing together experts from the different fields is an excellent means to achieve a deeper understanding of the phenomenon, especially for those objects that display a mix of properties, such as hot subdwarfs, central objects of planetary nebulae, γ Cas stars, or tepid Ap/Bp stars.
- Structures in stellar outflows
Stellar winds exhibit both small- and large-scale structures. The large-scale structures can result from the impact of magnetic fields on the stellar winds leading to co-rotating interaction regions or magnetically confined winds. In Oe/Be stars, disk-like outflows are produced by the large rotational velocities. Other factors that are likely to modulate the wind properties over relatively large scales are (non-radial) stellar pulsations. Beside the large-scale structures, small-scale structures, so-called clumps, are nowadays thought to be present in essentially all stellar winds. The properties of these structures can be studied via the spectral characteristics and the temporal variability of the X-ray emission of single massive stars. In addition, tremendous insight can be obtained from the study of high-mass X-ray binaries where the X-ray emission from the accreting compact object acts as a probe of the stellar wind.
- Interacting winds
Due to their highly supersonic velocities, stellar winds are bound to heavily interact with their surrounding medium. Examples of such interactions can be found in planetary nebulae, wind-blown bubbles, and bow-shocks around runaway stars. Based on first principles, these objects should be emitting X-rays, but observations have revealed a complex picture. Other wind interactions occur in massive binaries where the collision between the stellar winds leads to hydrodynamic shocks that heat the wind plasma to X-ray temperatures. In this case also, predictions have sometimes been challenged by observations. Whilst tremendous progress has been made in these fields thanks to the current generation of X-ray satellites, some questions just start to emerge from these results, and the preparation of the tools to analyze future observations with upcoming instrumentations need to be discussed.

Proposed SOC:
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Paula Benaglia (Argentina)
You-Hua Chu (China Taipei)
Kenji Hamaguchi (USA)
Yoshitomo Maeda (Japan)
Lida Oskinova (Germany)
Gregor Rauw (Belgium, chair)