5,688 research outputs found
A pair of gigantic bipolar dust jets close to the solar system
We report the discovery of two adjacent jet candidates with a length of about
9 degrees each -- 10 times longer than the largest known jets -- detected by us
on 60 and 100 micron IRAS maps, but not observed at any other wavelength. They
are extremely collimated (length-to-width ratios 20--50), curved, knotty, and
end in prominent bubbles. Their dust temperatures are 25 K and 30 K,
respectively. Both harbour faint stars, one having a high proper motion (0.23
arcsec/yr) and being very red, suggesting a distance of about 60 pc. At this
distance, the total mass of both jet candidates is about about 1 solar mass. We
suspect that these gigantic (9 pc length respectively) jets are of fossil type
and have a common origin, due to the decay of a system of evolved stars. They
are the first examples of jets radiating in the far IR and might, because of
their closeness, be of interest for further studies of the acceleration and
collimation processes of astrophysical jets.Comment: 4 pages, 4 figures in reduced quality, accepted by Astronomy &
Astrophysics (Letter) february 10, 2004. See
http://astro.uibk.ac.at/dustjets/ for the full resolution and color version
of the image
Ab-initio spin dynamics applied to nanoparticles: canted magnetism of a finite Co chain along a Pt(111) surface step edge
In order to search for the magnetic ground state of surface nanostructures we
extended first principles adiabatic spin dynamics to the case of fully
relativistic electron scattering. Our method relies on a constrained density
functional theory whereby the evolution of the orientations of the spin-moments
results from a semi-classical Landau-Lifshitz equation. This approach is
applied to a study of the ground state of a finite Co chain placed along a step
edge of a Pt(111) surface. As far as the ground state spin orientation is
concerned we obtain excellent agreement with the experiment. Furthermore we
observe noncollinearity of the atom-resolved spin and orbital moments. In terms
of magnetic force theorem calculations we also demonstrate how a reduction of
symmetry leads to the existence of canted magnetic states.Comment: 4 pages, ReVTeX + 3 figures (Encapsulated Postscript), submitted to
PR
Magnetic properties of Quantum Corrals from first principles calculations
We present calculations for electronic and magnetic properties of surface
states confined by a circular quantum corral built of magnetic adatoms (Fe) on
a Cu(111) surface. We show the oscillations of charge and magnetization
densities within the corral and the possibility of the appearance of
spin--polarized states. In order to classify the peaks in the calculated
density of states with orbital quantum numbers we analyzed the problem in terms
of a simple quantum mechanical circular well model. This model is also used to
estimate the behaviour of the magnetization and energy with respect to the
radius of the circular corral. The calculations are performed fully
relativistically using the embedding technique within the
Korringa-Kohn-Rostoker method.Comment: 14 pages, 9 figures, submitted to J. Phys. Cond. Matt. special issue
on 'Theory and Simulation of Nanostructures
Spin-polarized surface states close to adatoms on Cu(111)
We present a theoretical study of surface states close to 3d transition metal
adatoms (Cr, Mn, Fe, Co, Ni and Cu) on a Cu(111) surface in terms of an
embedding technique using the fully relativistic Korringa-Kohn-Rostoker method.
For each of the adatoms we found resonances in the s-like states to be
attributed to a localization of the surface states in the presence of an
impurity. We studied the change of the s-like densities of states in the
vicinity of the surface state band-edge due to scattering effects mediated via
the adatom's d-orbitals. The obtained results show that a magnetic impurity
causes spin-polarization of the surface states. In particular, the long-range
oscillations of the spin-polarized s-like density of states around an Fe adatom
are demonstrated.Comment: 5 pages, 5 figures, submitted to PR
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