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  Forward modelling of brightness variations in Sun-like stars: I. Emergence and surface transport of magnetic flux

Isik, E., Solanki, S. K., Krivova, N. A., & Shapiro, A. (2018). Forward modelling of brightness variations in Sun-like stars: I. Emergence and surface transport of magnetic flux. Astronomy and Astrophysics, 620: A177. doi:10.1051/0004-6361/201833393.

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Item Permalink: http://hdl.handle.net/21.11116/0000-0003-C2BF-B Version Permalink: http://hdl.handle.net/21.11116/0000-0004-B399-5
Genre: Journal Article

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 Creators:
Isik, Emre1, Author              
Solanki, Sami K.1, Author              
Krivova, Natalie A.1, Author              
Shapiro, Alexander1, 2, Author              
Affiliations:
1Department Sun and Heliosphere, Max Planck Institute for Solar System Research, Max Planck Society, ou_1832289              
2ERC Starting Grant: Connecting Solar and Stellar Variabilities (SOLVe), Max Planck Institute for Solar System Research, Max Planck Society, ou_3164811              

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Free keywords: stars: activity / stars: solar-type / starspots / stars: magnetic field / methods: numerical / magnetohydrodynamics (MHD)
 Abstract: Context. The latitudinal distribution of starspots deviates from the solar pattern with increasing rotation rate. Numerical simulations of magnetic flux emergence and transport can help model the observed stellar activity patterns and the associated brightness variations. Aims. We set up a composite model for the processes of flux emergence and transport on Sun-like stars to simulate stellar brightness variations for various levels of magnetic activity and rotation rates. Methods. Assuming that the distribution of magnetic flux at the base of the convection zone follows solar scaling relations, we calculate the emergence latitudes and tilt angles of bipolar regions at the surface for various rotation rates, using thin-flux-tube simulations. Taking these two quantities as input to a surface flux transport (SFT) model, we simulate the diffusive-advective evolution of the radial field at the stellar surface, including effects of active region nesting. Results. As the rotation rate increases, (1) magnetic flux emerges at higher latitudes and an inactive gap opens around the equator, reaching a half-width of 20° for 8 Ω⊙; and (2) the tilt angles of freshly emerged bipolar regions show stronger variations with latitude. Polar spots can form at 8 Ω⊙ by accumulation of follower-polarity flux from decaying bipolar regions. From 4 Ω⊙ to 8 Ω⊙, the maximum spot coverage changes from 3 to 20%, respectively, compared to 0.4% in the solar model. Nesting of activity can lead to strongly non-axisymmetric spot distributions. Conclusions. On Sun-like stars rotating at 8 Ω⊙ (Prot ≃ 3 days), polar spots can form, owing to higher levels of flux emergence rate and tilt angles. Defining spots by a threshold field strength yields global spot coverages that are roughly consistent with stellar observations.

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Language(s): eng - English
 Dates: 2018
 Publication Status: Published in print
 Pages: -
 Publishing info: -
 Table of Contents: -
 Rev. Method: Peer
 Identifiers: DOI: 10.1051/0004-6361/201833393
 Degree: -

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Project name : ERC-2016-STG - SOLVe
Grant ID : 715947
Funding program : Horizon 2020 (H2020)
Funding organization : European Commission (EC)

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Title: Astronomy and Astrophysics
  Other : Astron. Astrophys.
Source Genre: Journal
 Creator(s):
Affiliations:
Publ. Info: Les Ulis Cedex A France : EDP Sciences
Pages: - Volume / Issue: 620 Sequence Number: A177 Start / End Page: - Identifier: Other: 1432-0746
ISSN: 0004-6361
CoNE: https://pure.mpg.de/cone/journals/resource/954922828219_1