This week (28th Oct) the virtual Wednesday talk will be delivered by Dr. Alessia Franchini (Università Milano-Bicocca), who will present “Disc eccentricity driving type I and type II outbursts in Be/X-ray binaries”. Members of the School can access this seminar via Microsoft Teams
Title : Disc eccentricity driving type I and type II outbursts in Be/X-ray binaries.
Abstract: The majority of Be star X-ray binaries are transient systems and show two types of outbursts. Type I outbursts occur on the orbital period while type II or giant outbursts have a duration that is not related to any periodicity of the system.Type I outbursts can be explained with either the binary eccentricity or the presence of the 3:1 Lindblad resonance within a coplanar Be star disc while type II have been suggested to be triggered through Kozai-Lidov oscillations of a strongly misaligned decretion disc.
A sufficiently misaligned Be star decretion disc undergoes secular Kozai-Lidov oscillations of eccentricity and inclination and is able to Roche lobe overflow transferring mass over a longer timescale onto the companion neutron star.
I am going to give a general introduction on these fascinating systems and their properties. I will then present the results of new numerical hydrodynamical simulations that explore the dynamics of the Be star accretion disc and in particular aim at explaining the types of outbursts with the development of the disc eccentricity. I will discuss the dynamics of an initially highly inclined disc around the neutron star, formed as a consequence of Kozai-Lidov oscillations of the Be star disc and its effect on the neutron star accretion rate.
The seminar programme can be found at: https://www2.le.ac.uk/departments/physics/research/theoretical_astro/seminar-program/seminars.