19 avril 2012 : Physics of wind-accretion in microquasars and recurrent novae
Physics of wind-accretion in microquasars and recurrent novae
par Rolf Walder (Centre de Recherche Astrophysique de Lyon)
Jeudi 19 avril 2012, à 14h, bât. 121, salle 1-2-3
About half of the microquasar do not undergo Roche lobe overflow but are accreting from the powerful wind of a massive companion. Similarly, about half of the known 11 recurrent novae - likely progenitors of SNIa - are wind-accretors. Despite of its obvious importance, the physics of wind-accretion is hardly explored. Neither explored are the implications for the working mechanism and the emission of these high energy objects.
I will report on numerical simulations of wind accretion in both of these systems. I will demonstrate that wind-accretion is highly efficient in binary systems where the undergoes heavy mass loss via a strong wind. This work demonstrates that in such systems no classical Keplerian disk is formed. Depending on the wind speeds, two different modes are identified. Slow winds result in the formation of a geometrically thick disk. Angular momentum is advected by two strong shocks. Along the poles of the disk, a low density accretion funnel is located. Fast wind systems, on the other hand, hardly develop any disk at all. On the contrary, strong accretion filaments develop from a network of shocks due to different colliding accretion streams.
I will discuss the consequences for recurrent nova systems, arguing that such systems likely develop into an SNIa, either of the singly or the double degenerate type. The results for the microquasars are more preliminary but still allow to conclude that thermal flow structure is decisive - not only for the observed emission but also for the dynamics.
par Rolf Walder (Centre de Recherche Astrophysique de Lyon)
Jeudi 19 avril 2012, à 14h, bât. 121, salle 1-2-3
About half of the microquasar do not undergo Roche lobe overflow but are accreting from the powerful wind of a massive companion. Similarly, about half of the known 11 recurrent novae - likely progenitors of SNIa - are wind-accretors. Despite of its obvious importance, the physics of wind-accretion is hardly explored. Neither explored are the implications for the working mechanism and the emission of these high energy objects.
I will report on numerical simulations of wind accretion in both of these systems. I will demonstrate that wind-accretion is highly efficient in binary systems where the undergoes heavy mass loss via a strong wind. This work demonstrates that in such systems no classical Keplerian disk is formed. Depending on the wind speeds, two different modes are identified. Slow winds result in the formation of a geometrically thick disk. Angular momentum is advected by two strong shocks. Along the poles of the disk, a low density accretion funnel is located. Fast wind systems, on the other hand, hardly develop any disk at all. On the contrary, strong accretion filaments develop from a network of shocks due to different colliding accretion streams.
I will discuss the consequences for recurrent nova systems, arguing that such systems likely develop into an SNIa, either of the singly or the double degenerate type. The results for the microquasars are more preliminary but still allow to conclude that thermal flow structure is decisive - not only for the observed emission but also for the dynamics.