Convective overshoot and metal accretion onto white dwarfs.

• A large fraction of white dwarfs host evolved planetary systems and show evidence of accretion from planetary debris. The accretion-diffusion model is the preferred method to understand the metal pollution in these otherwise hydrogen- and helium-rich white dwarf atmospheres. In this scenario, the accreted material first settles on the atmosphere. If the outer stellar layers are unstable to convection, the metals are then rapidly mixed up within the convection zone. In the classical 1D approach, it is generally assumed that the convection zone has a sharp bottom boundary, below which microscopic diffusion is unhampered and slowly removes metals from the visible layers. More realistic 3D radiation-hydrodynamics simulations of white dwarfs with CO5BOLD demonstrate, however, that the bottom of the convection zone does not have a sharp boundary, and that velocities decay exponentially below the unstable convective layers with a velocity scale height of the order of one pressure scale height. This has a potentially dramatic effect on the inferred mass of accreted materiel, hence on the chemical composition and size of planetary debris around white dwarfs.

Ämnesord

NATURVETENSKAP  -- Fysik -- Astronomi, astrofysik och kosmologi (hsv//swe)

NATURAL SCIENCES  -- Physical Sciences -- Astronomy, Astrophysics and Cosmology (hsv//eng)

Nyckelord

convection

stars: interior

white dwarfs

Astronomy with specialization in Astrophysics

Astronomi med intiktning mot astrofysik

Publikations- och innehållstyp

vet (ämneskategori)

art (ämneskategori)