2,227 research outputs found
The cluster M-T relation from temperature profiles observed with ASCA and ROSAT
We calibrate the galaxy cluster mass - temperature relation using the
temperature profiles of intracluster gas observed with ASCA (for hot clusters)
and ROSAT (for cool groups). Our sample consists of apparently relaxed clusters
for which the total masses are derived assuming hydrostatic equilibrium. The
sample provides data on cluster X-ray emission-weighted cooling flow-corrected
temperatures and total masses up to r_1000. The resulting M-T scaling in the
1-10 keV temperature range is M_1000 = (1.23 +- 0.20)/h_50 10^15 Msun (T/10
keV)^{1.79 +- 0.14} with 90% confidence errors, or significantly (99.99%
confidence) steeper than the self-similar relation M propto T^{3/2}. For any
given temperature, our measured mass values are significantly smaller compared
to the simulation results of Evrard et al. (1996) that are frequently used for
mass-temperature scaling. The higher-temperature subsample (kT > 4 keV) is
consistent with M propto T^{3/2}, allowing the possibility that the
self-similar scaling breaks down at low temperatures, perhaps due to heating by
supernovae that is more important for low-temperature groups and galaxies as
suggested by earlier works.Comment: 8 pages, 2 figures, accepted by Ap
Methanol Droplet Extinction in Oxygen/Carbon-dioxide/Nitrogen Mixtures in Microgravity: Results from the International Space Station Experiments
Motivated by the need to understand the flammability limits of condensed-phase fuels in microgravity, isolated single droplet combustion experiments were carried out in the Combustion Integrated Rack Facility onboard the International Space Station. Experimental observations of methanol droplet combustion and extinction in oxygen/carbon-dioxide/nitrogen mixtures at 0.7 and 1 atmospheric pressure in quiescent microgravity environment are reported for initial droplet diameters varying between 2 mm to 4 mm in this study.The ambient oxygen concentration was systematically lowered from test to test so as to approach the limiting oxygen index (LOI) at fixed ambient pressure. At one atmosphere pressure, ignition and some burning were observed for an oxygen concentration of 13% with the rest being nitrogen. In addition, measured droplet burning rates, flame stand-off ratios, and extinction diameters are presented for varying concentrations of oxygen and diluents. Simplified theoretical models are presented to explain the observed variations in extinction diameter and flame stand-off ratios
Loop corrections for Kaluza-Klein AdS amplitudes
Recently we conjectured the four-point amplitude of graviton multiplets in
at one loop by exploiting the operator product
expansion of super Yang-Mills theory. Here we give the first
extension of those results to include Kaluza-Klein modes, obtaining the
amplitude for two graviton multiplets and two states of the first KK mode. Our
method again relies on resolving the large N degeneracy among a family of long
double-trace operators, for which we obtain explicit formulas for the leading
anomalous dimensions. Having constructed the one-loop amplitude we are able to
obtain a formula for the one-loop corrections to the anomalous dimensions of
all twist five double-trace operators.Comment: 37 pages. One ancillary file containing data on the correlator
Baryon Content of Massive Galaxy Clusters (0.57 < z < 1.33)
We study the stellar, Brightest Cluster Galaxy (BCG) and intracluster medium
(ICM) masses of 14 South Pole Telescope (SPT) selected galaxy clusters with
median redshift and median mass . We
estimate stellar masses for each cluster and BCG using six photometric bands
spanning the range from the ultraviolet to the near-infrared observed with the
VLT, HST and Spitzer. The ICM masses are derived from Chandra and XMM-Newton
X-ray observations, and the virial masses are derived from the SPT
Sunyaev-Zel'dovich Effect signature.
At the BCG mass constitutes %
of the halo mass for a cluster, and this fraction
falls as . The cluster stellar mass function has a
characteristic mass , and the number of
galaxies per unit mass in clusters is larger than in the field by a factor
. Both results are consistent with measurements on group scales and
at lower redshift. We combine our SPT sample with previously published samples
at low redshift that we correct to a common initial mass function and for
systematic differences in virial masses. We then explore mass and redshift
trends in the stellar fraction (fstar), the ICM fraction (fICM), the cold
baryon fraction (fc) and the baryon fraction (fb). At a pivot mass of
and redshift , the characteristic values are
fstar=%, fICM=%, fc=% and fb=%.
These fractions all vary with cluster mass at high significance, indicating
that higher mass clusters have lower fstar and fc and higher fICM and fb. When
accounting for a 15% systematic virial mass uncertainty, there is no
statistically significant redshift trend at fixed mass in these baryon
fractions.
(abridged)Comment: Accepted for publication in MNRA
In Situ Coordinated Analysis of Carbonaceous Chondrite Organic Matter
Microanalytical studies of carbonaceous chondrites (CCs) have identified a vast array of isotopically, chemically and texturally distinct organic components. These components were synthesized and processed within a range of physical and chemical environments, including the interstellar medium, the solar nebula and within asteroids. The nature and abundance of these molecules can be used to unravel the geochemical and isotopic record of their origins as well as their subsequent evolutionary journey
X-Ray Eclipse Time Delays in 4U2129+47
4U 2129+47 was discovered in the early 80's and classified as an accretion
disk corona source due to its broad and partial X-ray eclipses. The 5.24 hr
binary orbital period was inferred from the X-ray and optical light curve
modulation, implying a late K or M spectral type companion star.
The source entered a low state in 1983, during which the optical modulation
disappeared and an F8 IV star was revealed, suggesting that 4U 2129+47 might be
part of a triple system. The nature of 4U 2129+47 has since been investigated,
but no definitive conclusion has been reached.
Here, we present timing and spectral analyses of two XMM-Newton observations
of this source, carried out in May and June, 2005. We find evidence for a delay
between two mid-eclipse epochs measured ~22 days apart, and we show that this
delay can be naturally explained as being due to the orbital motion of the
binary 4U 2129+47 around the center of mass of a triple system. This result
thus provides further support in favor of the triple nature of 4U 2129+47.Comment: 6 pages, 5 figures, accepted by A&
Impacts on the CV parent body: a coordinated, multiscale fabric analysis of the Allende meteorite
Evidence of impact-induced compaction in the carbonaceous chondrites, specifically CMs and CVs, has been widely investigated utilizing microscopy techniques and impact experiments. Here, we use high-resolution photography and large area and high-resolution electron backscattered diffraction (EBSD) mapping analyses in tandem, to explore the effects of impact-induced compaction at both the meso- and micro-scales in the Allende CV3.6 carbonaceous chondrite. Macro-scale photography images of a ~25 cm slab of Allende captured meso-scale features including calcium-aluminum inclusions (CAIs) and chondrules. CAIs have a long-axis shape-preferred orientation (SPO). Examination of such meso-scale features in thin section revealed the same trend. Matrix grains from this section display a large amount of heterogeneity in petrofabric orientation; microscale, high-resolution, large area EBSD mapping of ~300,000 olivine matrix grains; high-resolution large area EBSD map across an elongate CAI; and a series of high-resolution EBSD maps around two chondrules and around the CAI revealed crystallographic preferred orientations (CPOs) in different directions. Finally, internal grains of the CAI were found to demonstrate a weak lineation CPO, the first crystallographic detection of possible CAI “flow.” All results are consistent with multiple, gentle impacts on the Allende parent body causing hemispheric compaction. The larger, more resistant components are likely to have been compressed and oriented by earlier impacts, and the matrix region petrofabrics and CAI “flow” likely occurred during subsequent impacts. Meteoritic components respond differently to impact events, and consequently, it is likely that different components would retain evidence of different impact events and angles
The Mid-Infrared Properties of X-ray Sources
We combine the results of the Spitzer IRAC Shallow Survey and the Chandra
XBootes Survey of the 8.5 square degrees Bootes field of the NOAO Deep Wide-
Field Survey to produce the largest comparison of mid-IR and X-ray sources to
date. The comparison is limited to sources with X-ray fluxes >8x10-15 erg
cm-2s-1 in the 0.5-7.0 keV range and mid-IR sources with 3.6 um fluxes brighter
than 18.4 mag (12.3 uJy). In this most sensitive IRAC band, 85% of the 3086
X-ray sources have mid-IR counterparts at an 80% confidence level based on a
Bayesian matching technique. Only 2.5% of the sample have no IRAC counterpart
at all based on visual inspection. Even for a smaller but a significantly
deeper Chandra survey in the same field, the IRAC Shallow Survey recovers most
of the X-ray sources. A majority (65%) of the Chandra sources detected in all
four IRAC bands occupy a well-defined region of IRAC [3.6] - [4.5] vs [5.8] -
[8.0] color-color space. These X-ray sources are likely infrared luminous,
unobscured type I AGN with little mid-infrared flux contributed by the AGN host
galaxy. Of the remaining Chandra sources, most are lower luminosity type I and
type II AGN whose mid-IR emission is dominated by the host galaxy, while
approximately 5% are either Galactic stars or very local galaxies.Comment: Accepted for publication in Ap
The Mass of the Compact Object in the X-Ray Binary Her X-1/HZ Her
We have obtained the first estimates of the masses of the components of the
Her X-1/HZ Her X-ray binary system taking into account non-LTE effects in the
formation of the H_gamma absorption line: mx=1.8Msun and mv=2.5Msun. These mass
estimates were made in a Roche model based on the observed radial-velocity
curve of the optical star, HZ Her. The masses for the X-ray pulsar and optical
star obtained for an LTE model lie are mx=0.85\pm0.15Msun and
mv=1.87\pm0.13Msun. These mass estimates for the components of Her X-1/HZ Her
derived from the radial-velocity curve should be considered tentative. Further
mass estimates from high-precision observations of the orbital variability of
the absorption profiles in a non-LTE model for the atmosphere of the optical
component should be made.Comment: 20 pages, 4 tables, 8 figure
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