37,922 research outputs found
XMM-Newton Detection of Hot Gas in the Eskimo Nebula: Shocked Stellar Wind or Collimated Outflows?
The Eskimo Nebula (NGC 2392) is a double-shell planetary nebula (PN) known
for the exceptionally large expansion velocity of its inner shell, ~90 km/s,
and the existence of a fast bipolar outflow with a line-of-sight expansion
velocity approaching 200 km/s. We have obtained XMM-Newton observations of the
Eskimo and detected diffuse X-ray emission within its inner shell. The X-ray
spectra suggest thin plasma emission with a temperature of ~2x10^6 K and an
X-ray luminosity of L_X = (2.6+/-1.0)x10^31 (d/1150 pc)^2 ergs/s, where d is
the distance in parsecs. The diffuse X-ray emission shows noticeably different
spatial distributions between the 0.2-0.65 keV and 0.65-2.0 keV bands.
High-resolution X-ray images of the Eskimo are needed to determine whether its
diffuse X-ray emission originates from shocked fast wind or bipolar outflows.Comment: 4 pages, 2 figures, accepted in Astronomy and Astrophysics Letter
Perfect State Transfer: Beyond Nearest-Neighbor Couplings
In this paper we build on the ideas presented in previous works for perfectly
transferring a quantum state between opposite ends of a spin chain using a
fixed Hamiltonian. While all previous studies have concentrated on
nearest-neighbor couplings, we demonstrate how to incorporate additional terms
in the Hamiltonian by solving an Inverse Eigenvalue Problem. We also explore
issues relating to the choice of the eigenvalue spectrum of the Hamiltonian,
such as the tolerance to errors and the rate of information transfer.Comment: 8 pages, 2 figures. Reorganised, more detailed derivations provided
and section on rate of information transfer adde
Diffuse X-ray Emission within Wolf-Rayet Nebulae
We discuss our most recent findings on the diffuse X-ray emission from
Wolf-Rayet (WR) nebulae. The best-quality X-ray observations of these objects
are those performed by XMM-Newton and Chandra towards S308, NGC2359, and
NGC6888. Even though these three WR nebulae might have different formation
scenarios, they all share similar characteristics: i) the main plasma
temperatures of the X-ray-emitting gas is found to be =[1-2]10
K, ii) the diffuse X-ray emission is confined inside the [O III] shell, and
iii) their X-ray luminosities and electron densities in the 0.3-2.0~keV energy
range are 10-10~erg~s and
0.1-1~cm, respectively. These properties and the
nebular-like abundances of the hot gas suggest mixing and/or thermal conduction
is taking an important role reducing the temperature of the hot bubble.Comment: 3 pages, 1 figure; International Workshop on Wolf-Rayet Star
Anisotropic charge dynamics in detwinned Ba(FeCo)As
We investigate the optical conductivity as a function of temperature with
light polarized along the in-plane orthorhombic - and -axes of
Ba(FeCo)As for =0 and 2.5 under uniaxial pressure.
The charge dynamics at low frequencies on these detwinned, single domain
compounds tracks the anisotropic transport properties across their
structural and magnetic phase transitions. Our findings allow us to estimate
the dichroism, which extends to relatively high frequencies. These results are
consistent with a scenario in which orbital order plays a significant role in
the tetragonal-to-orthorhombic structural transition
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