Magnetized Double-diffusive Convection in Stars

University Of California-Santa Cruz, Santa Cruz CA

Investigators

Abstract

Convection is the process by which heat is transferred by the bulk flow of fluid from one region to another. It is important in the Earth's atmosphere, in the oceans, in molten regions within the Earth, and inside stars. Double diffusive convection (DDC) occurs when convection is driven by two different density gradients in the fluid, each of which has a different rate of diffusion. An example is within the ocean, where heat and salt gradients drive convection at different rates. DDC could play an important role in stellar interiors. This team will study DDC in stars using numerical simulations, with an emphasis on the effect of magnetic fields on diffusion. The principal investigator will advise students as part of her project. She is also involved each year in running or participating in summer graduate training programs. As part of the project, she plans to run a Kavli Summer Program in Astrophysics on the topic of Mixing in Stars. The research team will continue its recent progress in characterizing the transport properties (for heat and chemical species primarily) of double-diffusive instabilities using numerical simulations. They will continue to investigate the effect of other processes, such as rotation and shear, and start to look into the effect of magnetic fields. Magnetic fields are very common in stars, but little work has been done to study their effect on other instabilities (beyond basic linear stability calculations). This group has shown that vertical magnetic fields can increase transport by fingering convection by orders of magnitude (contrary to linear work that had suggested it would decrease transport), with important consequences for mixing in red giant branch stars and white dwarfs. They will determine whether similar effects are possible for inclined fields and also study the interaction of magnetic fields with semiconvection, and they will characterize the dynamo properties of both fingering and oscillatory DDC, with and without rotation. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.