8,079 research outputs found
The luminosity function of cluster galaxies. II. Data reduction procedures applied to the cluster Abell 496
We initiated a large project aimed to estimate the Luminosity Function of
galaxies in clusters and to evaluate its relation to cluster morphology. With
this paper we deem necessary to outline the general procedures of the data
reduction and details of the data analysis. The cluster sample includes the
brightest southern ROSAT all-sky survey clusters with z < 0.1. These have been
observed in three colours g, r, i, and mapped up to a few core radii using a
mosaic of CCD frames. E/S0 galaxies in the cluster core are singled out both by
morphology (for the brightest galaxies), and by colour. The details of the data
reduction procedure are illustrated via the analysis of the cluster Abell 496,
which has been used as a pilot cluster for the whole program. The related
photometric catalogue consists of 2355 objects. The limiting magnitudes (the
reference Surface Brightness is given in parenthesis) in the various colours
are respectively g(25.5) = 24.14, r(25.5) = 24.46, i(25.0) = 23.75$. These
correspond to the limiting absolute magnitudes -12.28, -11.96 and -12.67
(H_0=50 km/sec/Mpc).Comment: 17 pages, 19 ps figures, aa.cl
Time-dependent Circulation Flows: Iron Enrichment in Cooling Flows with Heated Return Flows
We describe a new type of dynamical model for hot gas in galaxy groups and
clusters in which gas moves simultaneously in both radial directions.
Circulation flows are consistent with (1) the failure to observe cooling gas in
X-ray spectra, (2) multiphase gas observed near the centers of these flows and
(3) the accumulation of iron in the hot gas from Type Ia supernovae in the
central galaxy. Dense inflowing gas cools, producing a positive central
temperature gradient, as in normal cooling flows. Bubbles of hot, buoyant gas
flow outward. Circulation flows eventually cool catastrophically if the outward
flowing gas transports mass but no heat; to maintain the circulation both mass
and energy must be supplied to the inflowing gas over a large volume, extending
to the cooling radius. The rapid radial recirculation of gas produces a flat
central core in the gas iron abundance, similar to many observations. We
believe the circulation flows described here are the first gasdynamic,
long-term evolutionary models that are in good agreement with all essential
features observed in the hot gas: little or no gas cools as required by XMM
spectra, the gas temperature increases outward near the center, and the gaseous
iron abundance is about solar near the center and decreases outward.Comment: 17 pages (emulateapj5) with 6 figures; accepted by The Astrophysical
Journa
A self-consistent test of Comptonization models using a long BeppoSAX observation of NGC 5548
We test accurate models of Comptonization spectra over the high quality data
of the BeppoSAX long look at NGC 5548. The data are well represented by a plane
parallel corona with an inclination angle of 30, a soft photon
temperature of 5 eV and a hot plasma temperature and optical depth of 360 keV and 0.1, respectively. If energy balance
applies, such values suggest that a more ``photon-starved'' geometry (e.g. a
hemispheric region) is necessary. The spectral softening detected during a
flare, appears to be associated to a decrease of the heating-to-cooling ratio,
indicating a geometric and/or energetic modification of the disk plus corona
system. The hot plasma temperature derived with the models above is
significantly higher than that obtained fitting the same data with a power law
plus high energy cut off model for the continuum. This is due to the fact that
in anisotropic geometries Comptonization spectra show "intrinsic" curvature
which moves the fitted high energy cut-off to higher energies.Comment: 4 pages, 2 figures, to appear in the proceedings of the conference
"X-ray Astronomy '99", Bologna, Italy, September 199
Hard X-ray emission from the galaxy cluster A2256
After the positive detection by BeppoSAX of hard X-ray radiation up to ~80
keV in the Coma cluster spectrum, we present evidence for nonthermal emission
from A2256 in excess of thermal emission at a 4.6sigma confidence level. In
addition to this power law component, a second nonthermal component already
detected by ASCA could be present in the X-ray spectrum of the cluster, not
surprisingly given the complex radio morphology of the cluster central region.
The spectral index of the hard tail detected by the PDS onboard BeppoSAX is
marginally consistent with that expected by the inverse Compton model. A value
of ~0.05 microG is derived for the intracluster magnetic field of the extended
radio emission in the northern regions of the cluster, while a higher value of
\~0.5 microG could be present in the central radio halo, likely related to the
hard tail detected by ASCA.Comment: 10 pages, 2 figures. To appear in ApJ
Chopped random-basis quantum optimization
In this work we describe in detail the "Chopped RAndom Basis" (CRAB) optimal
control technique recently introduced to optimize t-DMRG simulations
[arXiv:1003.3750]. Here we study the efficiency of this control technique in
optimizing different quantum processes and we show that in the considered cases
we obtain results equivalent to those obtained via different optimal control
methods while using less resources. We propose the CRAB optimization as a
general and versatile optimal control technique.Comment: 9 pages, 10 figure
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