Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Forward modelling of brightness variations in Sun-like stars I.
  Emergence and surface transport of magnetic flux   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. 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. 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. 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 $20^\circ$ for $8\Omega_\odot$, (2) the tilt
angles of freshly emerged bipolar regions show stronger variations with
latitude. Polar spots can form at $8\Omega_\odot$ by accumulation of
follower-polarity flux from decaying bipolar regions. From $4\Omega_\odot$ to
$8\Omega_\odot$, the maximum spot coverage changes from 3 to 20%, respectively,
compared to 0.4% for the solar model. Nesting of activity can lead to strongly
non-axisymmetric spot distributions. On Sun-like stars rotating at
$8\Omega_\odot$ ($P_{\rm rot}\simeq 3$ 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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The categories of this paper are: acc-phys
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The categories of this paper are: nlin
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The categories of this paper are: q-fin
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The categories of this paper are: hep-th
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The categories of this paper are: hep-ph
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The categories of this paper are: chao-dyn
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The categories of this paper are: chem-ph
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The categories of this paper are: solv-int
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The categories of this paper are: supr-con
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The categories of this paper are: mtrl-th
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The categories of this paper are: ao-sci
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The categories of this paper are: nucl-ex
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The categories of this paper are: alg-geom
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The categories of this paper are: math-ph
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The categories of this paper are: cond-mat
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The categories of this paper are: nucl-th