1,629 research outputs found
Extended Thermal X-ray Emission from the Spiral-Dominant Group of Galaxies HCG 57
We observed a group of galaxies, HCG 57, with ASCA. Regardless that their
member galaxies are dominated by spiral galaxies, we detected extended thermal
X-ray emission that is attributed to hot gas with a temperature of
keV. This is the second clear detection of thermal X-ray emission
from a spiral-dominant group of galaxies after HCG 92. The luminosity of the
thermal emission is about erg s in the 0.5--10 keV
band, which is higher than that of HCG 92, but relatively less luminous among
groups of galaxies. The X-ray emission is extended over several member
galaxies, and is thus associated with the group rather than an individual
galaxy. The metal abundance cannot be well constrained with a lower limit of
0.08 solar. The gas-to-stellar mass ratio is . Although this is
relatively low among groups, the hot gas is also a significant component even
in the spiral-dominant group. We suggest that the X-ray faintness of
spiral-dominant groups is due to the low surface brightness and somewhat low
gas mass, at least in the case of HCG 57.Comment: 12 pages, 4 figures, to appear in PASJ 54 No.
Chandra X-Ray Spectral Analysis of Cooling Flow Clusters, 2A 0335+096 and Abell 2199
We report on a spatially resolved analysis of Chandra X-ray data on a nearby
typical cooling flow cluster of galaxies 2A 0335+096, together with A 2199 for
a comparison. As recently found in the cores of other clusters, the temperature
around the central part of 2A 0335+096 is 1.3--1.5 keV, which is higher than
that inferred from the cooling flow picture. Furthermore, the absorption column
density is almost constant against the radius in 2A 0335+096; there is no
evidence of excess absorption up to 200--250 kpc. This indicates that no
significant amount of cold material, which has cooled down, is present. These
properties are similar to those of A 2199. Since the cooling time in the
central part is much shorter than the age of the clusters, a heating mechanism,
which weakens the effect of radiative cooling, is expected to be present in the
central part of both clusters of galaxies. Both 2A 0335+096 and A 2199 have
radio jets associated with their cD galaxy. We discuss the possibility of
heating processes caused by these radio jets by considering the thermal
conduction and the sound velocity together with the observed disturbance of the
ICM temperature and density. We conclude that the observed radio jets can
produce local heating and/or cooling, but do not sufficiently reduce the
overall radiative cooling. This implies that much more violent jets, whose
emission has now decayed, heated up the cooling gas years ago.Comment: 13 pages, 7 figures, to appear in PASJ 55 No.
Influence of mechanical reinforcement of MgB2 wires on the superconducting properties
Monofilamentary MgB2-wires with a mechanical tough Nb/Cu/steel or Fe/steel
sheath were prepared and characterized. The steel content was varied to
investigate the reinforcement effect and the consequences for the
superconducting properties of the wires, which were heat treated to achieve
dense and homogeneous filaments. The use of Nb as first sheath layer, having a
smaller thermal expansion coefficient than MgB2, requires the application of
higher amounts of steel to achieve compressive pre-stress on the filament in
comparison to Fe as first wall material. With raised steel content in the
sheath the critical transport currents show field dependent significant
critical current and irreversibility field degradations. First Ic vs. axial
stress and strain experiments confirmed this observation of pre-stress induced
degradations. Consequences for improved wires and for future applications will
be discussed.Comment: 14 pages, 7 figures, 1 table; Submitted to Physica C; presentation at
ISS-2001, Kobe Japa
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