1 research outputs found
Abundance variations and first ionization potential trends during large stellar flares
The Solar First Ionization Potential (FIP) effect, where low-FIP elements are
enriched in the corona relative to the photosphere, while high-FIP abundances
remain unchanged, has been known for a long while. High resolution X-ray
spectroscopy has revealed that active stellar coronae show an opposite effect,
which was labeled the Inverse-FIP (IFIP) effect. The correlation found between
coronal activity and the FIP/IFIP bias suggested perhaps that flaring activity
is involved in switching from FIP to IFIP. This work aims at a more systematic
understanding of the FIP trends during stellar flares and complements an
earlier study based on Chandra alone. The eight brightest X-ray flares observed
with XMM-Newton are analyzed and compared with their respective quiescence
states. Together with six previous flares observed with Chandra, this
establishes the best currently available sample of flares. We look for
abundance variations during the flare and their correlation with FIP. For that
purpose, we define a new FIP bias measure. A trend is found where coronae that
are IFIP biased in quiescence, during flares show a FIP bias with respect to
their quiescence composition. This effect is reversed for coronae that are FIP
biased in quiescence. The observed trend is thus consistent with chromospheric
evaporation rather than with a FIP mechanism operating during flares. It also
suggests that the quiescent IFIP bias is real and that the large flares are not
the direct cause of the IFIP effect in stellar coronae.Comment: 12 pages, 6 figures, submitted to A&