86 research outputs found
High-resolution extreme ultraviolet spectroscopy of G191-B2B: structure of the stellar photosphere and the surrounding interstellar medium
We have continued our detailed analysis of the high-resolution (R= 4000) spectroscopic observation of the DA white dwarf G191-B2B, obtained by the Joint Astrophysical Plasmadynamic Experiment (J-PEX) normal incidence sounding rocket-borne telescope, comparing the observed data with theoretical predictions for both homogeneous and stratified atmosphere structures. We find that the former models give the best agreement over the narrow waveband covered by J-PEX, in conflict with what is expected from previous studies of the lower resolution but broader wavelength coverage Extreme Ultraviolet Explorer spectra. We discuss the possible limitations of the atomic data and our understanding of the stellar atmospheres that might give rise to this inconsistency. In our earlier study, we obtained an unusually high ionization fraction for the ionized He ii present along the line of sight to the star. In the present paper, we obtain a better fit when we assume, as suggested by Space Telescope Imaging Spectrograph results, that this He ii resides in two separate components. When one of these is assigned to the local interstellar cloud, the implied He ionization fraction is consistent with measurements along other lines of sight. However, the resolving power and signal-to-noise available from the instrument configuration used in this first successful J-PEX flight are not sufficient to clearly identify and prove the existence of the two components
USA Observation of Spectral and Timing Evolution During the 2000 Outburst of XTE J1550-564
We report on timing and spectral observations of the 2000 outburst of XTE
J1550-564 made by the Unconventional Stellar Aspect (USA) Experiment on board
the Advanced Research and Global Observation Satellite (ARGOS). We observe a
low-frequency quasi-periodic oscillation (LFQPO) with a centroid frequency that
tends to increase with increasing flux and a fractional rms amplitude which is
correlated with the hardness ratio. The evolution of the hardness ratio (4--16
keV/1--4 keV) with time and source flux is examined. The hardness-intensity
diagram (HID) shows a cyclical movement in the clockwise direction and possibly
indicates the presence of two independent accretion flows. We observe a
relationship between the USA 4--16 keV count rate and radio observations and
discuss this in the context of previously observed correlations between X-ray,
radio, optical and IR data. We examine our results in the context of models
invoking two accretion flows: a thin disk and a hot sub-Keplerian flow.Comment: 11 pages, 2 figure
USA and RXTE Observations of a Variable Low-Frequency QPO in XTE J1118+480
The USA experiment on ARGOS and RXTE have exensively observed the X-ray
transient XTE J1118+480 during its recent outburst in 2000 April--June. We
present detailed monitoring of the evolution of a low frequency QPO which
drifts from 0.07 Hz to 0.15 Hz during the outburst. We examine possible
correlations of the QPO frequency with the flux and spectral characteristics of
the source, and compare this QPO to low frequency QPOs observed in other black
hole candidates.Comment: Accepted by ApJ Letters, reference added, minor revisions, 6 page
The ROSAT All-Sky Survey: a Catalog of Clusters of Galaxies in a Region of 1 Ster around the South Galactic Pole
A field of 1.013 ster in the ROSAT all-sky survey (RASS), centered on the
south galactic pole (SGP), has been searched in a systematic, objective manner
for clusters of galaxies. The procedure relied on a correlation of the X-ray
positions and properties of ROSAT sources with the distribution of galaxies in
the COSMOS digitised data base, which was obtained by scanning the plates of
the UK Schmidt IIIa-J optical southern sky survey. The study used the second
ROSAT survey data base (RASS-2) and included several optical observing
campaigns to measure redshifts. The search, a precursor to the larger REFLEX
survey of the whole southern sky, reached the detection limits of the RASS and
the COSMOS data, and yielded a catalog of 186 clusters in which the lowest flux
is 1.5e-12 erg/cm2/s in the 0.1-2.4 keV band. Of these 157 have measured
redshifts. Using a limit of 3.0e-12 erg/cm2/s a complete subset of 112 clusters
was obtained, of which 110 have measured redshifts. The spatial distribution of
the X-ray clusters out to z = 0.15 shows an extension of the Local Supercluster
to the Pisces-Cetus supercluster (z<~0.07), and a more distant orthogonal
structure at 0.07<z<0.15.Comment: To be published in ApJ Supplements in February 2002: 53 pages: 18
figure
Quasi-Periodic Occultation by a Precessing Accretion Disk and Other Variabilities of SMC X-1
We have investigated the variability of the binary X-ray pulsar, SMC X-1, in
data from several X-ray observatories. We confirm the ~60-day cyclic variation
of the X-ray flux in the long-term monitoring data from the RXTE and CGRO
observatories. X-ray light curves and spectra from the ROSAT, Ginga, and ASCA
observatories show that the uneclipsed flux varies by as much as a factor of
twenty between a high-flux state when 0.71 second pulses are present and a
low-flux state when pulses are absent. In contrast, during eclipses when the
X-rays consist of radiation scattered from circumsource matter, the fluxes and
spectra in the high and low states are approximately the same. These
observations prove that the low state of SMC X-1 is not caused by a reduction
in the intrinsic luminosity of the source, or a spectral redistribution
thereof, but rather by a quasi-periodic blockage of the line of sight, most
likely by a precessing tilted accretion disk. In each of two observations in
the midst of low states a brief increase in the X-ray flux and reappearance of
0.71 second pulses occurred near orbital phase 0.2. These brief increases
result from an opening of the line of sight to the pulsar that may be caused by
wobble in the precessing accretion disk. The records of spin up of the neutron
star and decay of the binary orbit are extended during 1991-1996 by
pulse-timing analysis of ROSAT, ASCA, and RXTE PCA data. The pulse profiles in
various energy ranges from 0.1 to >21 keV are well represented as a combination
of a pencil beam and a fan beam. Finally, there is a marked difference between
the power spectra of random fluctuations in the high-state data from the RXTE
PCA below and above 3.4 keV. Deviation from the fitted power law around 0.06 Hz
may be QPO.Comment: Accepted to ApJ. 33 pages including 11 figure
A Search for Aperiodic Millisecond Variability in Cygnus X-1
We have conducted a search for aperiodic millisecond variability in the
integrated 1 to 25 keV X-ray region of Cyg X-1. We have examined HEAO A-1
archival data and Rossi X-ray Timing Explorer (RXTE) guest observer data for
evidence of excess power above the Poisson noise floor using the relative
integral power analysis and the Fourier transform method. Our results are in
disagreement with the results of Meekins et al. (1984). We attribute the
discrepancy to an instrumental effect for which Meekins et al.(1984) did not
apply a correction. With the correction we see no evidence for excess power
above 25 Hz in the HEAO A-1 data. Our analysis of RXTE data is in agreement
with previously published results of different data sets and shows no sign of
excess power above 30 Hz.Comment: 29 pages, 12 figures, to be submitted to Ap
Comparison of glottic views and intubation times in the supine and 25 degree back-up positions
Background: We explored whether positioning patients in a 25° back-up sniffing position improved glottic views
and ease of intubation.
Methods: In the first part of the study, patients were intubated in the standard supine sniffing position. In the
second part, the back of the operating table was raised 25° from the horizontal by flexion of the torso at the hips
while maintaining the sniffing position. The best view obtained during laryngoscopy was assessed using the
Cormack and Lehane classification and Percentage of Glottic Opening (POGO) score. The number of attempts at
both laryngoscopy and tracheal intubation, together with the use of ancillary equipment and manoeuvres were
recorded. The ease of intubation was indirectly assessed by recording the time interval between beginning of
laryngoscopy and insertion of the tracheal tube.
Results: Seven hundred eighty one unselected surgical patients scheduled for non-emergency surgery were
included. In the back-up position, ancillary laryngeal manoeuvres, which included cricoid pressure, backwards
upwards rightward pressure and external laryngeal manipulation, were required less frequently (19.6 % versus 24.
6 %, p = 0.004). The time from beginning of laryngoscopy to insertion of the tracheal tube was 14 % shorter
(median time 24 versus 28 s, p = 0.031) in the back-up position. There was no significant difference in glottic views.
Conclusions: The 25° back-up position improved the ease of intubation as judged by the need for fewer ancillary
manoeuvres and shorter time for intubation.
Trial registration: ClinicalTrials.gov Identifier: NCT02934347 registered retrospectively on 14th Oct 2016
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