Magnetic Archaeology of Early-Type Stellar Dynamos

Abstract

Early-type stars show a bimodal distribution of magnetic field strengths, with some showing very strong fields ($\gtrsim 1\mathrm{kG}$) and others very weak fields ($\lesssim 10\mathrm{G}$). Recently, we proposed that this reflects the processing or lackthereof of fossil fields by subsurface convection zones. Stars with weak fossil fields process these at the surface into even weaker dynamo-generated fields, while in stars with stronger fossil fields magnetism inhibits convection, allowing the fossil field to remain as-is. We now expand on this theory and explore the time-scales involved in the evolution of near-surface magnetic fields. We find that mass loss strips near-surface regions faster than magnetic fields can diffuse through them. As a result, observations of surface magnetism directly probe the frozen-in remains of the convective dynamo. This explains the slow evolution of magnetism in stars with very weak fields: these dynamo-\emph{generated} magnetic fields evolve on the time-scale of the mass loss, not that of the dynamo.

12 pages, 7 figures, accepted in ApJ

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Cited by in corpus (2)

• An Atlas of Convection in Main-Sequence Stars
• Ultraviolet Spectropolarimetric Diagnostics of Hot Star Magnetospheres