85 research outputs found
Simulating coronal condensation dynamics in 3D
We present numerical simulations in 3D settings where coronal rain phenomena
take place in a magnetic configuration of a quadrupolar arcade system. Our
simulation is a magnetohydrodynamic simulation including anisotropic thermal
conduction, optically thin radiative losses, and parametrised heating as main
thermodynamical features to construct a realistic arcade configuration from
chromospheric to coronal heights. The plasma evaporation from chromospheric and
transition region heights eventually causes localised runaway condensation
events and we witness the formation of plasma blobs due to thermal instability,
that evolve dynamically in the heated arcade part and move gradually downwards
due to interchange type dynamics. Unlike earlier 2.5D simulations, in this case
there is no large scale prominence formation observed, but a continuous coronal
rain develops which shows clear indications of Rayleigh-Taylor or interchange
instability, that causes the denser plasma located above the transition region
to fall down, as the system moves towards a more stable state. Linear stability
analysis is used in the non-linear regime for gaining insight and giving a
prediction of the system's evolution. After the plasma blobs descend through
interchange, they follow the magnetic field topology more closely in the lower
coronal regions, where they are guided by the magnetic dips.Comment: 47 pages, 59 figure
Stellar energetic particles in the magnetically turbulent habitable zones of TRAPPIST-1-like planetary systems
Planets in close proximity to their parent star, such as those in the
habitable zones around M dwarfs, could be subject to particularly high doses of
particle radiation. We have carried out test-particle simulations of ~GeV
protons to investigate the propagation of energetic particles accelerated by
flares or travelling shock waves within the stellar wind and magnetic field of
a TRAPPIST-1-like system. Turbulence was simulated with small-scale
magnetostatic perturbations with an isotropic power spectrum. We find that only
a few percent of particles injected within half a stellar radius from the
stellar surface escape, and that the escaping fraction increases strongly with
increasing injection radius. Escaping particles are increasingly deflected and
focused by the ambient spiralling magnetic field as the superimposed turbulence
amplitude is increased. In our TRAPPIST-1-like simulations, regardless of the
angular region of injection, particles are strongly focused onto two caps
within the fast wind regions and centered on the equatorial planetary orbital
plane. Based on a scaling relation between far-UV emission and energetic
protons for solar flares applied to M dwarfs, the innermost putative habitable
planet, TRAPPIST-1e, is bombarded by a proton flux up to 6 orders of magnitude
larger than experienced by the present-day Earth. We note two mechanisms that
could strongly limit EP fluxes from active stars: EPs from flares are contained
by the stellar magnetic field; and potential CMEs that might generate EPs at
larger distances also fail to escape.Comment: 17 pages, 12 figures, ApJ in pres
X-rays Studies of the Solar System
X-ray observatories contribute fundamental advances in Solar System studies
by probing Sun-object interactions, developing planet and satellite surface
composition maps, probing global magnetospheric dynamics, and tracking
astrochemical reactions. Despite these crucial results, the technological
limitations of current X-ray instruments hinder the overall scope and impact
for broader scientific application of X-ray observations both now and in the
coming decade. Implementation of modern advances in X-ray optics will provide
improvements in effective area, spatial resolution, and spectral resolution for
future instruments. These improvements will usher in a truly transformative era
of Solar System science through the study of X-ray emission.Comment: White paper submitted to Astro2020, the Astronomy and Astrophysics
Decadal Surve
Effects of flavonoids dietary supplementation on milk antioxidant capacity in sheep
Hesperidin and naringin are bioflavonoids known for their antioxidant properties. They are abundant in inexpensive by-products of citrus cultivation such as citrus pulp which often are treated as waste. An experiment was conducted to examine the effects of dietary hesperidin or naringin supplementation on lactating ewes’ milk antioxidant capacity
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