1,207 research outputs found
X-ray bursters and the X-ray sources of the galactic bulge
Type 1 X-ray bursts, optical, infrared, and radio properties of the galactic bulge sources, are discussed. It was proven that these burst sources are neutron stars in low mass, close binary stellar systems. Several burst sources are found in globular clusters with high central densities. Optical type 1 X-ray bursts were observed from three sources. Type 2 X-ray bursts, observed from the Rapid Burster, are due to an accretion instability which converts gravitational potential energy into heat and radiation, which makes them of a fundamentally different nature from Type 1 bursts
High content image-based cytometry as a tool for nuclear fingerprinting
Cytomics aims at understanding the functional relationships between cellular phenotypes (cytome) and metabolic pathways (proteome) that result from a combination of genetically defined mechanisms (genome) and environmental conditions [1,2]. Although flow-cytometry is able to measure the optical properties of single cells at a rate of >1000 cells per minute it has a limited capability of mapping individual events. To accurately quantify (sub-) cellular characteristics within a natural context there is a fast-growing need for image-based cytometry. Images, obtained with fluorescence microscopy, provide the exact information on signal intensity, location and distribution of specific molecules within intact cell systems (tissue or monolayers) and allow for investigating cellular properties in relation to the cell-ecological context [3]. Previously, we have developed a cytometric approach for scoring DNA lesion endpoints in confocal images of murine fibroblasts [3]. We now present a generalized approach for multivariate phenotypic profiling of individual nuclei using automated fluorescence mosaic microscopy and optimized digital image processing tools. An indefinite number of fields, z-slices and channels can be analyzed; the only prerequisite is the presence of a nuclear counterstain, which is used for the generation of masks. To anticipate for erroneous segmentation of clustered nuclei in dense cell cultures we implemented an iterative conditional segmentation (ics) algorithm that uses both morphological and intensity information from the image (Figure 1). The method makes use of a priori knowledge about the size and shape of nuclei in stringent feedback selection of correctly segmented nuclei. Depending on the degree of clustering, segmentation performance varies between 95% and 100%. Complete analysis of nuclei and subnuclear features for a region of 25 images of 1000x1000 pixels, 3 z-slices and 3 channels only takes ~ 3 minutes or ~ 0.7sec/nucleus. Our method is insensitive to scaling, illumination heterogeneity and variability or non-uniformity of staining. We have successfully applied our system in cell cycle analysis, scoring of transfection efficiency and assessment of (localized) DNA damage in response to genotoxic stress and ionizing radiation
Hysteresis in the de Haas-van Alphen Effect
A hysteresis loop is observed for the first time in the de Haas-van Alphen
(dHvA) effect of beryllium at low temperatures and quantizing magnetic field
applied parallel to the hexagonal axis of the single crystal. The irreversible
behavior of the magnetization occurs at the paramagnetic part of the dHvA
period in conditions of Condon domain formation arising by strong enough dHvA
amplitude. The resulting extremely nonlinear response to a very small
modulation field offers the possibility to find in a simple way the Condon
domain phase diagram. From a harmonic analysis, the shape and size of the
hysteresis loop is constructed.Comment: 4 pages, 5 figures, submitted to PR
Tightly Correlated X-ray/H Emitting Filaments in the Superbubble and Large-Scale Superwind of NGC 3079
Using Chandra and HST we show that X-ray and H filaments that form
the 1.3-kpc diameter superbubble of NGC 3079 have strikingly similar patterns
at 0."8 resolution. This tight match seems to arise from cool disk gas that has
been driven by the wind, with X-rays being emitted from upstream, stand-off
bowshocks or by conductive cooling at the cloud/wind interfaces. We find that
the soft X-ray plasma has thermal and kinetic energies of
and erg
respectively, where is the filling factor of the X-ray gas and may be
small; these are comparable to the energies of the optical line-emitting gas.
X-rays are also seen from the base of the radio counterbubble that is obscured
optically by the galaxy disk, and from the nucleus (whose spectrum shows the Fe
K line). Hydrodynamical simulations reproduce the obbservations well
using large filling factors within both filament systems; assuming otherwise
seriously underestimates the mass loss in the superwind. The superbubble is
surrounded by a fainter conical halo of X-rays that fill the area delineated by
high angle, H-emitting filaments, supporting our previous assertion
that these filaments form the contact discontinuity/shock between galaxy gas
and shocked wind. About 40\arcsec (3 kpc) above the disk, an X-ray arc may
partially close beyond the bubble, but the north-east quadrant remains open,
consistent with the superwind having broken out into at least the galaxy halo.Comment: 8 pages, 3 figures, to appear in Sept. 10 Ap
Direct Observation of Condon Domains in Silver by Hall Probes
Using a set of micro Hall probes for the detection of the local induction,
the inhomogeneous Condon domain structure has been directly observed at the
surface of a pure silver single crystal under strong Landau quantization in
magnetic fields up to 10 T. The inhomogeneous induction occurs in the
theoretically predicted part of the H-T Condon domain phase diagram.
Information about size, shape and orientation of the domains is obtained by
analyzing Hall probes placed along and across the long sample axis and by
tilting the sample. On a beryllium surface the induction inhomogeneity is
almost absent although the expected induction splitting here is at least ten
times higher than in silver.Comment: 4 pages, 6 figures, submitted to PR
A Search for High-Excitation Redshift Systems in the Absorption Spectra of Five Quasars
We have searched the absorption spectra of five quasars for the presence of redshift system dominated by the highly ionized doublets C iv, N v, and O vi, which could be the strongest lines produced by absorbing clouds with collisional ionization temperatures between 10^5 ° and 10^6 °K. There is at most marginal evidence for one such system apiece in the spectra of PHL 957 and 4C 05.34, which are the two quasars with the largest known emission redshifts. Highly ionized redshift systems of this type are not widespread among the five quasars we investigated; the number of redshifts found in the observed spectra is not significantly larger than the number found in similar random-number spectra. Less than 5 percent of the observed absorption lines are identified in a statistically significant way by redshift systems of this type
A Technique for Narrowband Time Series Photometry: the X-ray Star V2116 Oph
We have used innovative features of the Taurus Tunable Filter instrument on
the 3.9-m Anglo-Australian Telescope to obtain nearly-continuous,
high-throughput, linear photometry of V2116 Oph in a 7 Angstrom bandpass at the
center of the O I 8446 emission line. This instrumental technique shows promise
for applications requiring precise, rapid, narrowband photometry of faint
objects. The spectrum of V2116 Oph, the counterpart of GX 1+4 (=X1728-247), is
exotic, even among the unusual spectra of other optical counterparts of compact
Galactic X-ray sources. The second strongest emission line is an unusual one,
namely extremely prominent O I 8446, which is likely to result from pumping by
an intense Ly beta radiation field. As the X-radiation from GX 1+4 is steadily
pulsed, with typical pulsed fractions of 0.4, the O I 8446 emission in V2116
Oph may also be strongly modulated with the current 127 s period of the X-ray
source. If so, this may well allow us to obtain high signal-to-noise radial
velocity measurements and thus to determine the system parameters. However, no
such pulsations are detected, and we set an upper limit of ~1% (full-amplitude)
on periodic 8446 oscillations at the X-ray frequency. This value is comparable
to the amplitude of continuum oscillations observed on some nights by other
workers. Thus we rule out an enhancement of the pulsation amplitude in O I
emission, at least at the time of our observations.Comment: 9 pages including 4 figures and no tables. Accepted for publication
in PASP; to appear in Volume 110, August 199
The Absence of Extra-Tidal Structure in the Sculptor Dwarf Spheroidal Galaxy
The results of a wide-field survey of the Sculptor dwarf spheroidal galaxy
are presented. Our aims were to obtain an accurate map of the outer structure
of Sculptor, and to determine the level of interaction between this system and
the Galaxy. Photometry was obtained in two colours down to the magnitude limits
of V=20 and I=19, covering a 3.1 times 3.1 square deg area centred on Sculptor.
The resulting colour-magnitude data were used as a mask to select candidate
horizontal branch and red giant branch stars for this system. Previous work has
shown that the red horizontal branch (HB) stars are more concentrated than the
blue HB stars. We have determined the radial distributions of these two
populations and show that the overall Sculptor density profile is well
described by a two component model based on a combination of these radial
distributions. Additionally, spectra of the Ca ii triplet region were obtained
for over 700 candidate red giant stars over the 10 square deg region using the
2dF instrument on the Anglo-Australian Telescope. These spectra were used to
remove foreground Galactic stars based on radial velocity and Ca ii triplet
strength. The final list of Sculptor members contained 148 stars, seven of
which are located beyond the nominal tidal radius. Both the photometric and
spectroscopic datasets indicate no significant extra-tidal structure. These
results support at most a mild level of interaction between this system and the
Galaxy, and we have measured an upper mass limit for extra-tidal material to be
2.3 +/- 0.6% of the Sculptor luminous mass. This lack of tidal interaction
indicates that previous velocity dispersion measurements (and hence the amount
of dark matter detected) in this system are not strongly influenced by the
Galactic tidal field.Comment: 53 pages, 23 figures. Accepted for publication in the Astronomical
Journal. Some figures are reduced in size, and a full version is available
at: ftp://ftp.mso.anu.edu.au/pub/coleman/sculptor.pd
The Photonic TIGER: a multicore fiber-fed spectrograph
We present a proof of concept compact diffraction limited high-resolution
fiber-fed spectrograph by using a 2D multicore array input. This high
resolution spectrograph is fed by a 2D pseudo-slit, the Photonic TIGER, a
hexagonal array of near-diffraction limited single-mode cores. We study the
feasibility of this new platform related to the core array separation and
rotation with respect to the dispersion axis. A 7 core compact Photonic TIGER
fiber-fed spectrograph with a resolving power of around R~31000 and 8 nm
bandwidth in the IR centered on 1550 nm is demonstrated. We also describe
possible architectures based on this concept for building small scale compact
diffraction limited Integral Field Spectrographs (IFS).Comment: 8 pages, 6 figures, SPIE Astronomical Telescopes and Instrumentation
8450-5
- âŠ