Formation of starspots in self-consistent global dynamo models: Polar spots on cool stars

Context. Observations of cool stars reveal dark spot-like features on their surfaces. These starspots can be more extended than sunspots and cover a large area of the stellar surface. While sunspots appear only at low latitudes, starspots are also found in polar regions, in particular on rapidly rot...

Full description

Saved in:
Bibliographic Details
Published in:Astronomy and astrophysics (Berlin) 2015-01, Vol.573, p.A68
Main Authors: Yadav, Rakesh K., Gastine, Thomas, Christensen, Ulrich R., Reiners, Ansgar
Format: Article
Language:English
Subjects:
Computer simulation
convection
dynamo
Formations
Mathematical models
Rotating
Rotating generators
Spots
stars: interiors
stars: magnetic field
stars: rotation
Starspots
Sunspots
Citations: Items that this one cites
Items that cite this one
Online Access:Get full text
Tags: Add Tag
No Tags, Be the first to tag this record!
Description
Summary:Context. Observations of cool stars reveal dark spot-like features on their surfaces. These starspots can be more extended than sunspots and cover a large area of the stellar surface. While sunspots appear only at low latitudes, starspots are also found in polar regions, in particular on rapidly rotating stars. Conventional flux-tube models have been invoked to explain starspot properties. However, these models use several simplifications, and so far, neither sunspots nor starspots have been generated in a self-consistent simulation of stellar magnetic convection. Aims. We aim to clarify the conditions necessary for the spontaneous formation of dark spots in numerical models of convection-driven stellar dynamos. Methods. We simulated convection and magnetic field generation in rapidly rotating spherical shells assuming anelastic approximation. The high-resolution simulations were performed using a fully spectral magnetohydrodynamic code. Results. We demonstrate for the first time that a self-consistent distributed dynamo can spontaneously generate high-latitude dark spots. Dark spots are generated when a large-scale magnetic field, generated in the bulk of the convection zone, interacts with and locally quenches flow near the surface. Sufficiently strong density stratification and rapid rotation are prerequisites for the formation of sizeable dark spots in the model. Conclusions. Our models present an alternative scenario for starspot formation by distributed dynamo action. Our results also lend strong support to the idea that dynamos in the interiors of rapidly rotating stars might be fundamentally different from the solar one.
ISSN:0004-6361
1432-0746
DOI:10.1051/0004-6361/201424589