Wednesday Colloquium


"Complex evolutionary and asteroseismic modelling of pulsating components in eclipsing binary systems"

Amadeusz Miszuda (CAMK, Warsaw)

Eclipsing binary systems are well-proven benchmarks in testing stellar evolution theory. Precise stellar parameters that can come from their analysis aid systems' age determination along with tracing back their evolution history. Eclipsing binaries that contain pulsating components are a special subclass of binaries that combine information coming from orbital and pulsational analyses. Whereas the single-star pulsators are rather well understood, the precise effect that binarity and possible mass transfer have on the pulsational characteristics of components has yet to be determined. In my talk, I will highlight some of the most important results from my studies of pulsating components in binary systems. In particular I will discuss the effect that accumulation of He in outer layers of accretor caused by mass transfer has on excitation of the high radial-order g modes in models of delta Scuti stars and the evolution of radial mode frequencies during the main sequence evolutionary phase.


"Magnetic white dwarfs in close binaries: origin, evolution, surfeit, and dearth"

Diogo Belloni (Departamento de Física, Universidad Técnica Federico Santa María)

Since the 1940s, understanding why some white dwarfs become strongly magnetized while others do not has been one of the fundamental unsolved issues of stellar evolution. Several models have been suggested for the magnetic field generation in white dwarfs, but they all fail when confronted with the observed incidence of magnetism in single white dwarfs and white dwarfs in binaries. We recently suggested that a rotation- and crystallization-driven dynamo, similar to those operating in planets and low-mass stars, is responsible for a large fraction of the observed strongly magnetized white dwarfs. During this talk, I will show that this new scenario can explain the existence of pulsar-like white dwarfs, the absence of bright X-ray accreting white dwarfs in globular clusters, the accumulation of magnetic white dwarfs among metal-polluted white dwarfs, the occurrence rate of strong magnetic fields in double white dwarf binaries, the paucity of white dwarfs accreting from brown dwarfs, and why a large fraction of accreting white dwarfs but only a small part of their detached progenitors contain a strongly magnetized white dwarf. That implies a rotation- and crystallization-driven dynamo most likely plays an unprecedentedly important role in the magnetic field generation in white dwarfs.