79 research outputs found
X-ray Point Sources in the Sombrero Galaxy: Supersoft sources, the globular cluster/LMXB connection, and an overview
We report on the population of point sources discovered during an 18.5 ksec
Chandra ACIS-S observation of the Sombrero Galaxy. We present the luminosity
function, the spectra of the 6 brightest sources, consider correlations with
globular clusters (GCs) and with planetary nebulae (PNe), and study the
galaxy's population of SSSs. We detected 122 sources, 22 of them are identified
as luminous supersoft X-ray sources (SSSs). There is an over density of SSSs
within 1.5 kpc of the nucleus, which is itself the brightest X-ray source. SSSs
are also found in the disk and halo, with 1 SSS in a globular cluster (GC).
Several sources in Sombrero's halo are good candidates for SSS models in which
the accretor is a nuclear-burning white dwarf. In total, 32 X-ray sources are
associated with GCs. The majority of sources with luminosity > 1e38 erg/s are
in GCs. These results for M104, an Sa galaxy, are similar to what has been
found for elliptical galaxies and for the late-type spiral M31. We find that
those optically bright GCs with X-ray sources house only the brightest X-ray
sources. We find that, in common with other galaxies, there appears to be a
positive connection between young (metal-rich) GCs and X-ray sources, but that
the brightest X-ray sources are equally likely to be in metal-poor GCs. We
propose a model which can explain the trends seen in the data sets from the
Sombrero and other galaxies. Thermal-time scale mass transfer can occur in some
of the the younger clusters in which the turn-off mass is slightly greater than
; multiplicity may play a role in some of the most massive
clusters; accretion from giant stars may be the dominant mechanism in some
older, less massive and less centrally concentrated clusters.Comment: 13 pages, 7 figures. ApJ submitte
Episodic Memory in Detoxified Alcoholics: Contribution of Grey Matter Microstructure Alteration
Even though uncomplicated alcoholics may likely have episodic memory deficits, discrepancies exist regarding to the integrity of brain regions that underlie this function in healthy subjects. Possible relationships between episodic memory and 1) brain microstructure assessed by magnetic resonance diffusion tensor imaging (DTI), 2) brain volumes assessed by voxel-based morphometry (VBM) were investigated in uncomplicated, detoxified alcoholics
LOFAR Low-Band antenna observations of the 3C 295 and Boötes fields: source counts and ultra-steep spectrum sources
We present Low Frequency Array (LOFAR) Low Band observations of the Boötes and 3C 295 fields. Our images made at 34, 46, and 62 MHz reach noise levels of 12, 8, and 5 mJy beam-1, making them the deepest images ever obtained in this frequency range. In total, we detect between 300 and 400 sources in each of these images, covering an area of 17-52 deg2. From the observations, we derive Euclidean-normalized differential source counts. The 62 MHz source counts agree with previous GMRT 153 MHz and Very Large Array 74 MHz differential source counts, scaling with a spectral index of -0.7. We find that a spectral index scaling of -0.5 is required to match up the LOFAR 34 MHz source counts. This result is also in agreement with source counts from the 38 MHz 8C survey, indicating that the average spectral index of radio sources flattens toward lower frequencies. We also find evidence for spectral flattening using the individual flux measurements of sources between 34 and 1400 MHz and by calculating the spectral index averaged over the source population. To select ultra-steep spectrum (α < -1.1) radio sources that could be associated with massive high-redshift radio galaxies, we compute spectral indices between 62 MHz, 153 MHz, and 1.4 GHz for sources in the Boötes field. We cross-correlate these radio sources with optical and infrared catalogs and fit the spectral energy distribution to obtain photometric redshifts. We find that most of these ultra-steep spectrum sources are located in the 0.7 âČ z âČ 2.5 range
Comparison of cell ultrastructure of an experimental ascites tumour of the mouse at different ages after transplantation.
ELECTRON MICROSCOPY OF THE CIRCULAR KINETOPLASTIC DNA FROM TRYPANOSOMA CRUZI: OCCURRENCE OF CATENATED FORMS
ABNORMAL CIRCULAR DNA MOLECULES INDUCED BY ETHIDIUM BROMIDE IN THE KINETOPLAST OF Trypanosoma cruzi
2005 Annual Status Report: A Summary of Fish Data in Six Reaches of the Upper Mississippi River System
From the Long Term Resource Monitoring Program (LTRMP) of the Upper Mississippi Rive
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