Modeling Time-Variable Elemental Abundances in Coronal Loop Simulations
The Astrophysical Journal Letters(2024)
摘要
Numerous recent X-ray observations of coronal loops in both active regions
(ARs) and solar flares have shown clearly that elemental abundances vary with
time. Over the course of a flare, they have been found to move from coronal
values towards photospheric values near the flare peak, before slowly returning
to coronal values during the gradual phase. Coronal loop models typically
assume that the elemental abundances are fixed, however. In this work, we
introduce a time-variable abundance factor into the 0D ebtel++ code that models
the changes due to chromospheric evaporation in order to understand how this
affects coronal loop cooling. We find that for strong heating events (≳
1 erg s^-1 cm^-3), the abundances quickly tend towards photospheric
values. For smaller heating rates, the abundances fall somewhere between
coronal and photospheric values, causing the loop to cool more quickly than the
time-fixed photospheric cases (typical flare simulations) and more slowly than
time-fixed coronal cases (typical AR simulations). This suggests heating rates
in quiescent AR loops no larger than ≈ 0.1 erg s^-1 cm^-3 to be
consistent with recent measurements of abundance factors f ≳ 2.
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关键词
The Sun,Solar coronal heating,Solar coronal loops,Solar flares
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