Title: Investigating the origin of small-scale magnetic fields on the Sun and other cool main-sequence stars

Abstract: Spectro-polarimetric observations show that the solar atmosphere is permeated by magnetic fields on spatial scales ranging from the 30000 km of super-granular cells, down to the smallest magnetic features resolvable with current instruments of scales less than 100 km. These small-scale magnetic fields are ubiquitous on the solar surface. Recent observations also show that they are independent of the solar cycle in internetwork regions. To explain this behavior, it is generally assumed that large-scale (i.e., comparable to the size of the system) magnetic fields are generated by the action of a global dynamo operating in the solar convection zone, whereas small-scale (i.e., size smaller than a solar granule) magnetic fields are, at least partially, sustained by a turbulent dynamo at play beneath the solar surface. Similar magnetic activities are expected to take place also on stars other than the Sun.

Numerical experiments provide an invaluable tool for investigating the functioning of dynamo action, both at small and large scales. In the present talk, we report on our recent work for estimating the effective Reynolds and magnetic Reynolds numbers that characterize plasma flows in radiative MHD simulations. Knowing these parameters is of paramount importance in the context of small-scale dynamo simulations. We then investigate how different flow parameters affect the results of small-scale solar dynamo simulations carried out with the CO5BOLD  code. To broaden our view on the solar magnetic activity, and at the same time improve our understanding of small-scale magnetic fields on other stellar atmospheres, we then extend our study to other main-sequence stars, thus investigating how small-scale dynamo action operates in F5V, G2V, K2V, and K8V stars. Finally, we present future perspectives for CO5BOLD simulations.

• Date:
  July 6, 2023, 2 p.m. – 4 p.m.
  
  
• Location:

  Schwarzschildhaus Lecture Hall

  
  
• Contact:
  Julián Alvarado-Gómez