Astrophysics Formal Seminars

Formal seminars take place every Monday during full term. For a complete list of talks please visited the website.

Stellar pulsation: excitation, diagnosis and seismology

Pulsations in stars across the Hertzsprung-Russell diagram are caused by the excitation of normal modes of oscillation by various means. The classical opacity (or kappa-gamma) mechanism responsible for the well-known Cepheid variables relies on peaks in the internal opacity – temperature distribution in a star. Starting from both linear and non-linear models, we will discuss the internal stellar chemistries that lead such peaks to produce pulsations in many classes of evolved star. We will explore one star in particular, V652 Her, where high-precision observations of large amplitude pulsations can be directly compared with hydrodynamic models, and we shall demonstrate how pulsations studies can reveal a star’s hidden past.

Unveiling the role of dust on planetary migration

Gas and dust are essential components of protoplanetary disks, actively participating in the formation of planetesimals and planetary bodies. The gravity of planetary embryos perturbs the disk which, in turn, reacts producing gravitational feedback onto the nascent planets. This feedback has the potential of changing the planets’ orbits, leading to a process known as planetary migration. The characterization of this migration requires detailed calculations of the global disk structure and detailed physical models. For example, the headwind exerted by a sub-Keplerian gas flow onto dust particles produces a mutual radial drift which, combined with planet torques, may have a significant effect on the resulting local mass distribution of the disk. This dust torque could—depending on the dust-to-gas mass ratio, the particle-size distribution, and the mass of the embryos—modify the orbit of the nascent planets. In this talk, I will present recent results related to torques induced by scattered pebble-flows in protoplanetary disks, obtained with the new multifluid version of the publicly available code FARGO3D .