Séminaires

A Few Topics in Nonlinear and Binary Asteroseismology
Zhao Guo (KULeuven)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

Stellar oscillations are not necessarily linear. Some oscillation modes can be weakly nonlinear and may produce daughter modes via parametric instability. This process is a potential amplitude limitation mechanism that determines the final observed oscillation amplitude, as demonstrated in Delta Scuti stars and Slowly Pulsating B stars. Observational signatures of nonlinear mode coupling include periodic amplitude and phase modulations. The behavior of a coupled-mode system can be rich and complex, including period doubling, intermittency, and various pathways to chaos. In some binary star systems with elliptical orbits, tidal forces can directly induce stellar gravity modes, manifesting as luminosity variations at orbital harmonic frequencies. These tidally excited oscillations (TEOs) can mostly be understood within the framework of linear theory. However, nonlinearity can induce non-orbital harmonic TEOs, and we can use these secondary modes to pioneer a new approach to asteroseismology. Finally, I will present another aspect of the nonlinear effect: wave-mean flow interactions. The quadratic terms in the wave equations can modify the background mean flow, and vice versa. We employ a quasi-linear approximation to study the spin-up of the solar core by the ingoing gravity waves induced by a planet, comparing it with direct numerical simulations.

A multimessenger GW-GRB study of the sGRB population and its future developments
Matteo Pracchia (Université de Liège)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)

The unambiguous joint detection of GRB 170817A and GW170817 has been the long-awaited smoking gun for the association between short gamma-ray bursts (sGRBs) and the merger of binary neutron stars (BNS) systems. The aforementioned sGRB, however, was extremely close and had an unexpectedly low measured luminosity when compared to the other observed sGRBs, suggesting that there is a sub-luminous fraction of the GRB population which is undetected at the usually measured distances.

This work aims to characterize the low-luminosity part of the sGRB population through a multi-messenger GW-GRB Bayesian study. The sGRB population is described via its luminosity probability distribution, modelled through an extension of a broken power law whose parameters have already been constrained through mid-high luminosity sGRB observations. The parameters of this power-law extension, i.e. the low luminosity power index and the low-luminosity cutoff, are constrained through a Bayesian analysis which exploits the results from the modelled GW follow-up analysis of the short GRBs detected during the first three observing runs of the International Gravitational-Wave observatory Network (IGWN).

The results obtained allow us to define the luminosity distribution at lower values for the sGRB population and to give an estimate of the value found for the astrophysical sGRB rate and the joint GW-GRB detection rate for the next IGWN observing runs. There are, nonetheless, some upgrades to the method used for this study that could give a more precise and complete outline of the astrophysical sGRB population.

TBA
Dixeena Lopez (Université de Liège)

Le lieu où se tiendra cet évènement n'est pas encore déterminé...

TBA
Victoria Bonidie (Pittsburgh University)

Salle de réunion AGO (local -1/14), Institut d'Astrophysique et de Géophysique
Bâtiment B5c, Quartier Agora, Allée du 6 Août, 19C, B-4000 Liège 1 (Sart-Tilman)