952 research outputs found
Emission lines of Fe XI in the 257--407 A wavelength region observed in solar spectra from EIS/Hinode and SERTS
Theoretical emission-line ratios involving Fe XI transitions in the 257-407 A
wavelength range are derived using fully relativistic calculations of radiative
rates and electron impact excitation cross sections. These are subsequently
compared with both long wavelength channel Extreme-Ultraviolet Imaging
Spectrometer (EIS) spectra from the Hinode satellite (covering 245-291 A), and
first-order observations (235-449 A) obtained by the Solar Extreme-ultraviolet
Research Telescope and Spectrograph (SERTS). The 266.39, 266.60 and 276.36 A
lines of Fe XI are detected in two EIS spectra, confirming earlier
identifications of these features, and 276.36 A is found to provide an electron
density diagnostic when ratioed against the 257.55 A transition. Agreement
between theory and observation is found to be generally good for the SERTS data
sets, with discrepancies normally being due to known line blends, while the
257.55 A feature is detected for the first time in SERTS spectra. The most
useful Fe XI electron density diagnostic is found to be the 308.54/352.67
intensity ratio, which varies by a factor of 8.4 between N_e = 10^8 and 10^11
cm^-3, while showing little temperature sensitivity. However, the 349.04/352.67
ratio potentially provides a superior diagnostic, as it involves lines which
are closer in wavelength, and varies by a factor of 14.7 between N_e = 10^8 and
10^11 cm^-3. Unfortunately, the 349.04 A line is relatively weak, and also
blended with the second-order Fe X 174.52 A feature, unless the first-order
instrument response is enhanced.Comment: 9 pages, 5 figures, 13 tables; MNRAS in pres
Soft X-ray emission lines of Fe XV in solar flare observations and the Chandra spectrum of Capella
Recent calculations of atomic data for Fe XV have been used to generate
theoretical line ratios involving n = 3-4 transitions in the soft X-ray
spectral region (52-83 A), for a wide range of electron temperatures and
densities applicable to solar and stellar coronal plasmas. A comparison of
these with solar flare observations from a rocket-borne spectrograph (XSST)
reveals generally good agreement between theory and experiment. In particular,
the 82.76 A emission line in the XSST spectrum is identified, for the first
time to our knowledge in an astrophysical source. Most of the Fe XV transitions
which are blended have had the species responsible clearly identified, although
there remain a few instances where this has not been possible. The line ratio
calculations are also compared with a co-added spectrum of Capella obtained
with the Chandra satellite, which is probably the highest signal-to-noise
observation achieved for a stellar source in the 25-175 A soft X-ray region.
Good agreement is found between theory and experiment, indicating that the Fe
XV lines are reliably detected in Chandra spectra, and hence may be employed as
diagnostics to determine the temperature and/or density of the emitting plasma.
However the line blending in the Chandra data is such that individual emission
lines are difficult to measure accurately, and fluxes may only be reliably
determined via detailed profile fitting of the observations. The co-added
Capella spectrum is made available to hopefully encourage further exploration
of the soft X-ray region in astronomical sources.Comment: 27 pages, 10 figures, Astrophysical Journal, in pres
The Homogeneity of Interstellar Oxygen in the Galactic Disk
We present an analysis of high resolution HST Space Telescope Imaging
Spectrograph (STIS) observations of O I 1356 and H I Lyman-alpha absorption in
36 sight lines that probe a variety of Galactic disk environments and include
paths that range over nearly 4 orders of magnitude in f(H_2), over 2 orders of
magnitude in mean sight line density, and that extend up to 6.5 kpc in length.
Consequently, we have undertaken the study of gas-phase O/H abundance ratio
homogeneity using the current sample and previously published Goddard
High-Resolution Spectrograph (GHRS) results. Two distinct trends are identified
in the 56 sight line sample: an apparent decrease in gas-phase oxygen abundance
with increasing mean sight line density and a gap between the mean O/H ratio
for sight lines shorter and longer than about 800 pc. The first effect is a
smooth transition between two depletion levels associated with large mean
density intervals; it is centered near a density of 1.5 cm^-3 and is similar to
trends evident in gas-phase abundances of other elements. Paths less dense than
the central value exhibit a mean O/H ratio of log_10 (O/H) = -3.41+/-0.01 (or
390+/-10 ppm), which is consistent with averages determined for several long,
low-density paths observed by STIS (Andre et al. 2003) and short low-density
paths observed by FUSE (Moos et al. 2002). Sight lines of higher mean density
exhibit an average O/H value of log_10 (O/H) = -3.55+/-0.02 (284+/-12 ppm). The
datapoints for low-density paths are scattered more widely than those for
denser sight lines, due to O/H ratios for paths shorter than 800 pc that are
generally about 0.10 dex lower than the values for longer ones.Comment: 33 pages, including 8 figures and 4 tables; accepted for publication
in ApJ, tentatively in Oct 200
Boron Abundances in Main Sequence B-type Stars: A Test of Rotational Depletion during Main Sequence Evolution
Boron abundances have been derived for seven main sequence B-type stars from
HST STIS spectra around the B III 2066 A line. In two stars, boron appears to
be undepleted with respect to the presumed initial abundance. In one star,
boron is detectable but it is clearly depleted. In the other four stars, boron
is undetectable implying depletions of 1 to 2 dex. Three of these four stars
are nitrogen enriched, but the fourth shows no enrichment of nitrogen. Only
rotationally induced mixing predicts that boron depletions are unaccompanied by
nitrogen enrichments. The inferred rate of boron depletion from our
observations is in good agreement with these predictions. Other boron-depleted
nitrogen-normal stars are identified from the literature. Also, several
boron-depleted nitrogen-rich stars are identified, and while all fall on the
boron-nitrogen trend predicted by rotationally-induced mixing, a majority have
nitrogen enrichments that are not uniquely explained by rotation.
The spectra have also been used to determine iron-group (Cr, Mn, Fe, and Ni)
abundances. The seven B-type stars have near solar iron-group abundances, as
expected for young stars in the solar neighborhood. We have also analysed the
halo B-type star, PG0832+676. We find [Fe/H] = -0.88 +/- 0.10, and the absence
of the B III line gives the upper limit [B/H]<2.5. These and other published
abundances are used to infer the star's evolutionary status as a post-AGB star.Comment: 31 pages, 14 figures. accepted to Ap
Unilateral thoracoscopic surgical approach for diffuse emphysema
AbstractWe evaluated the use of a lateral thoracoscopic approach for lung reduction surgery in patients with diffuse emphysema. Sixty-seven patients with a mean age of 61.9 years underwent operation. Operative side was determined by preoperative imaging. The procedures were laser ablation in 10 patients and stapler resection in 57 patients. Ten patients, including six of the 10 patients in the laser-only group had poor outcome (death or hospitalization longer than 30 days), leading us to abandon the laser technique. Of the remaining 57 patients undergoing primary stapled resection, duration of chest tube placement averaged 13 days (range 3 to 53 days) with a mean hospital stay of 17 days (range 6 to 99 days). Seven patients required ventilation for longer than 72 hours, six patients underwent conversion of the procedure to open thoracotomy, four patients acquired arrhythmias, and three patients were treated for empyema. There was one early death (1.7%), from cardiopulmonary failure. Forty patients returned for 3-month evaluation. Significant ( p < 0.0001) improvements were seen in forced vital capacity (2.69 L after vs 2.26 L before) and forced expiration volume in 1 second (1.04 L after vs 0.82 L before), with 25 of 40 patients (63%) showing an improvement of more than 20%. Lung volume measures, in particular residual volume, fell significantly. Arterial blood gas analysis revealed that carbon dioxide tension fell significantly in patients with preoperative hypercapnia (carbon dioxide tension >45 mm Hg, p = 0.018). Six-minute walk test results improved (894 feet after vs 784 feet before, p = 0.002), and symptomatic benefit was confirmed by significant improvement in the dyspnea index. The combination of both hypercapnia and reduced single-breath diffusing capacity for carbon monoxide was significantly more frequent ( p = 0.0026) and was 86% specific (5 of 6 patients) in predicting serious postoperative risk. We conclude that the lateral thoracoscopic surgical approach to diffuse emphysema offers significant improvement in pulmonary mechanics and functional impairment. Patients with a combination of hypercapnia and reduced single-breath diffusing capacity for carbon monoxide should not be considered for this procedure because of significant perioperative risk. (J THORAC CARDIOVASC SURG 1996;111:308-16
Tests of stellar model atmospheres by optical interferometry III: NPOI and VINCI interferometry of the M0 giant gamma Sge covering 0.5 - 2.2 microns
Aims: We present a comparison of the visual and NIR intensity profile of the
M0 giant gamma Sagittae to plane-parallel ATLAS 9 as well as to plane-parallel
& spherical PHOENIX model atmospheres. Methods: We use previously described
visual interferometric data obtained with the NPOI in July 2000. We apply the
recently developed technique of coherent integration, and thereby obtain
visibility data of more spectral channels and with higher precision than
before. In addition, we employ new measurements of the K-band diameter of gamma
Sagittae obtained with the instrument VINCI at the VLTI in 2002. Results: The
spherical PHOENIX model leads to a precise definition of the Rosseland angular
diameter and a consistent high-precision diameter value for our NPOI and
VLTI/VINCI data sets of Theta_Ross=6.06 pm 0.02 mas, with the Hipparcos
parallax corresponding to R_Ross=55 pm 4 R_sun, and with the bolometric flux
corresponding to an effective temperature T_eff=3805 pm 55 K. Our visual
visibility data close to the first minimum and in the second lobe constrain the
limb-darkening effect and are generally consistent with the model atmosphere
predictions. The visual closure phases exhibit a smooth transition between 0
and pi. Conclusions: The agreement between the NPOI and VINCI diameter values
increases the confidence in the model atmosphere predictions from optical to
NIR wavelengths as well as in the calibration and accuracy of both
interferometric facilities. The consistent night-by-night diameter values of
VINCI give additional confidence in the given uncertainties. The closure phases
suggest a slight deviation from circular symmetry, which may be due to surface
features, an asymmetric extended layer, or a faint unknown companion.Comment: 12 pages, 9 figures, accepted by A&A. Also available from
http://www.aanda.org/articles/aa/pdf/forth/aa5853_06.pd
Line formation regions of the UV spectrum of CI Cygni
We have examined radial velocities and fluxes of ultraviolet emission lines
at different epochs, deduced from archival IUE and GRHS/HST spectra. The line
fluxes give electron densities and were in addition used to calculate emission
measures, suggesting line formation in regions rather smaller than the binary
separation. Examination of the radial velocities led to us to find a systematic
redshift of the high ionization resonance lines with respect to the
intercombination, and HeII lines. Possible explanations of the redshift and the
high resolution GHRS CIV profile are discussed. We favour that involving
resonance line absorption by a circum-binary region most probably in an
asymmetric wind interaction shell or in a wind from the accretion disk.Comment: 8 pages, 4 figures, A&A accepte
The High Velocity Gas toward Messier 5: Tracing Feedback Flows in the Inner Galaxy
We present Far Ultraviolet Spectroscopic Explorer (FUSE) and Space Telescope
Imaging Spectrograph (STIS E140M) observations of the post-asymptotic giant
branch star ZNG 1 in the globular cluster Messier 5 (l=3.9, b=+47.7; d=7.5 kpc,
z=+5.3 kpc). High velocity absorption is seen in C IV, Si IV, O VI, and lower
ionization species at LSR velocities of -140 and -110 km/s. We conclude that
this gas is not circumstellar on the basis of photoionization models and path
length arguments. Thus, the high velocity gas along the ZNG 1 sight line is the
first evidence that highly-ionized HVCs can be found near the Galactic disk. We
measure the metallicity of these HVCs to be [O/H]=+0.22\pm0.10, the highest of
any known HVC. Given the clouds' metallicity and distance constraints, we
conclude that these HVCs have a Galactic origin. This sight line probes gas
toward the inner Galaxy, and we discuss the possibility that these HVCs may be
related to a Galactic nuclear wind or Galactic fountain circulation in the
inner regions of the Milky Way.Comment: 23 pages, 11 figures, 7 table
Best Practices for Siting Solar Photovoltaics on Municipal Solid Waste Landfills. A Study Prepared in Partnership with the Environmental Protection Agency for the RE-Powering America's Land Initiative: Siting Renewable Energy on Potentially Contaminated Land and Mine Sites
The Environmental Protection Agency and the National Renewable Energy Laboratory developed this best practices document to address common technical challenges for siting solar photovoltaics (PV) on municipal solid waste (MSW) landfills. The purpose of this document is to promote the use of MSW landfills for solar energy systems. Closed landfills and portions of active landfills with closed cells represent thousands of acres of property that may be suitable for siting solar photovoltaics (PV). These closed landfills may be suitable for near-term construction, making these sites strong candidate to take advantage of the 30% Federal Business Energy Investment Tax Credit. It was prepared in response to the increasing interest in siting renewable energy on landfills from solar developers; landfill owners; and federal, state, and local governments. It contains examples of solar PV projects on landfills and technical considerations and best practices that were gathered from examining the implementation of several of these projects
CRIRES-POP: A library of high resolution spectra in the near-infrared
New instrumental capabilities and the wealth of astrophysical information
extractable from the near-infrared wavelength region have led to a growing
interest in the field of high resolution spectroscopy at 1-5 mu. We aim to
provide a library of observed high-resolution and high signal-to-noise-ratio
near-infrared spectra of stars of various types throughout the
Hertzsprung-Russell diagram. This is needed for the exploration of spectral
features in this wavelength range and for comparison of reference targets with
observations and models.
High quality spectra were obtained using the CRIRES near-infrared
spectrograph at ESO's VLT covering the range from 0.97 to 5.3 mu at high
spectral resolution. Accurate wavelength calibration and correction for of
telluric lines were performed by fitting synthetic transmission spectra for the
Earth's atmosphere to each spectrum individually. We describe the observational
strategy and the current status and content of the library which includes 13
objects. The first examples of finally reduced spectra are presented. This
publication will serve as a reference paper to introduce the library to the
community and explore the extensive amount of material.Comment: accepted for publication in A&A; see also the project webpage
http://www.univie.ac.at/crirespo
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