Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Coronal activity cycles in nearby G and K stars - XMM-Newton monitoring
  of 61 Cygni and Alpha Centauri   We use X-ray observations of the nearby binaries 61 Cyg A/B (K5V and K7V) and
Alpha Cen A/B (G2V and K1V) to study the long-term evolution of magnetic
activity in weakly to moderately active G + K dwarfs over nearly a decade.
Specifically we search for X-ray activity cycles and related coronal changes
and compare them to the solar behavior. For 61 Cyg A we find a regular coronal
activity cycle analog to its 7.3 yr chromospheric cycle. The X-ray brightness
variations are with a factor of three significantly lower than on the Sun, yet
the changes of coronal properties resemble the solar behavior with larger
variations occurring in the respective hotter plasma components. 61 Cyg B does
not show a clear cyclic coronal trend so far, but the X-ray data matches the
more irregular chromospheric cycle. Both Alpha Cen stars exhibit significant
long-term X-ray variability. Alpha Cen A shows indications for cyclic
variability of an order of magnitude with a period of about 12-15 years; the
Alpha Cen B data suggests an X-ray cycle with an amplitude of about six to
eight and a period of 8-9 years. The sample stars exhibit X-ray luminosities
ranging between Lx < 1x10^26 - 3x10^27 erg s^-1 in the 0.2-2.0 keV band and
have coronae dominated by cool plasma with variable average temperatures of
around 1.0-2.5 MK. We find that coronal activity cycles are apparently a common
phenomenon in older, slowly rotating G and K stars. The spectral changes of the
coronal X-ray emission over the cycles are solar-like in all studied targets.

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The categories of this paper are: comp-gas
2
The categories of this paper are: math
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The categories of this paper are: patt-sol
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The categories of this paper are: adap-org
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The categories of this paper are: plasm-ph
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The categories of this paper are: econ
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The categories of this paper are: quant-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: mtrl-th
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The categories of this paper are: dg-ga
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The categories of this paper are: hep-th
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The categories of this paper are: nlin
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The categories of this paper are: math-ph
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The categories of this paper are: nucl-th
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The categories of this paper are: eess
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The categories of this paper are: chem-ph