113 research outputs found
The Fragmenting Superbubble Associated with the HII Region W4
New observations at high latitudes above the HII region W4 show that the
structure formerly identified as a chimney candidate, an opening to the
Galactic halo, is instead a superbubble in the process of fragmenting and
possibly evolving into a chimney. Data at high Galactic latitudes (b > 5
degrees) above the W3/W4 star forming region at 1420 and 408 MHz Stokes I
(total power) and 1420 MHz Stokes Q and U (linear polarization) reveal an
egg-shaped structure with morphological correlations between our data and the
H-alpha data of Dennison, Topasna, & Simonetti. Polarized intensity images show
depolarization extending from W4 up the walls of the superbubble, providing
strong evidence that the radio continuum is generated by thermal emission
coincident with the H-alpha emission regions. We conclude that the parts of the
HII region hitherto known as W4 and the newly revealed thermal emission are all
ionized by the open cluster OCl 352. Assuming a distance of 2.35 kpc, the ovoid
structure is 164 pc wide and extends 246 pc above the mid-plane of the Galaxy.
The shell's emission decreases in total-intensity and polarized intensity in
various locations, appearing to have a break at its top and another on one
side. Using a geometric analysis of the depolarization in the shell's walls, we
estimate that a magnetic field line-of-sight component of 3 to 5 uG exists in
the shell. We explore the connection between W4 and the Galactic halo,
considering whether sufficient radiation can escape from the fragmenting
superbubble to ionize the kpc-scale H-alpha loop discovered by Reynolds,
Sterling & Haffner.Comment: 42 pages, 14 figures; Accepted for publication in Ap
Probing the Interstellar Medium using HI absorption and emission towards the W3 HII region
HI spectra towards the W3 HII complex are presented and used to probe the
Galactic structure and interstellar medium conditions between us and this
region. The overall shape of the spectra is consistent with the predictions of
the Two-Arm Spiral Shock model wherein the gas found in the -40 km/s to -50
km/s range has been accelerated by some 20 km/s from its rotation curve
velocity. Spin temperatures of ~100 K are derived for the Local Arm gas, lower
than found in a previous, similar study towards DR 7. For the interarm region,
values on the order of 300 K are found, implying a negligible filling factor
for the Cold Neutral Medium (<< 1%). Some of the absorbing gas at velocities
near -40 km/s is confirmed to be associated with the HII regions.Comment: 23 pages, 6 figures, accepted for publication in the Astronomical
Journa
Radio polarimetric imaging of the interstellar medium: magnetic field and diffuse ionized gas structure near the W3/W4/W5/HB3 complex
We have used polarimetric imaging to study the magneto-ionic medium of the
Galaxy, obtaining 1420 MHz images with an angular resolution of 1' over more
than 40 square-degrees of sky around the W3/W4/W5/HB3 HII region/SNR complex in
the Perseus Arm. Features detected in polarization angle are imposed on the
linearly polarized Galactic synchrotron background emission by Faraday rotation
arising in foreground ionized gas having an emission measure as low as 1
cm^{-6} pc. Several new remarkable phenomena have been identified, including:
mottled polarization arising from random fluctuations in a magneto-ionic screen
that we identify with a medium in the Perseus Arm, probably in the vicinity of
the HII regions themselves; depolarization arising from very high rotation
measures (several times 10^3 rad m^{-2}) and rotation measure gradients due to
the dense, turbulent environs of the HII regions; highly ordered features
spanning up to several degrees; and an extended influence of the HII regions
beyond the boundaries defined by earlier observations. In particular, the
effects of an extended, low-density ionized halo around the HII region W4 are
evident, probably an example of the extended HII envelopes postulated as the
origin of weak recombination-line emission detected from the Galactic ridge.
Our polarization observations can be understood if the uniform magnetic field
component in this envelope scales with the square-root of electron density and
is 20 microG at the edge of the depolarized region around W4, although this is
probably an over-estimate since the random field component will have a
significant effect.Comment: 18 pages, 8 figures (7 jpeg and 1 postscript), accepted for
publication in the Astrophysical Journa
The Fourth SeaWiFS HPLC Analysis Round-Robin Experiment (SeaHARRE-4)
Ten international laboratories specializing in the determination of marine pigment concentrations using high performance liquid chromatography (HPLC) were intercompared using in situ samples and a mixed pigment sample. Although prior Sea-viewing Wide Field-of-view Sensor (SeaWiFS) High Performance Liquid Chromatography (HPLC) Round-Robin Experiment (SeaHARRE) activities conducted in open-ocean waters covered a wide dynamic range in productivity, and some of the samples were collected in the coastal zone, none of the activities involved exclusively coastal samples. Consequently, SeaHARRE-4 was organized and executed as a strictly coastal activity and the field samples were collected from primarily eutrophic waters within the coastal zone of Denmark. The more restrictive perspective limited the dynamic range in chlorophyll concentration to approximately one and a half orders of magnitude (previous activities covered more than two orders of magnitude). The method intercomparisons were used for the following objectives: a) estimate the uncertainties in quantitating individual pigments and higher-order variables formed from sums and ratios; b) confirm if the chlorophyll a accuracy requirements for ocean color validation activities (approximately 25%, although 15% would allow for algorithm refinement) can be met in coastal waters; c) establish the reduction in uncertainties as a result of applying QA procedures; d) show the importance of establishing a properly defined referencing system in the computation of uncertainties; e) quantify the analytical benefits of performance metrics, and f) demonstrate the utility of a laboratory mix in understanding method performance. In addition, the remote sensing requirements for the in situ determination of total chlorophyll a were investigated to determine whether or not the average uncertainty for this measurement is being satisfied
Spider silk protein structure analysis by FTIR and STXM spectromicroscopy techniques
Spider silk displays incredible strength and elasÂŹticity for its size and weight.[1] These properties have sparked interest in determining the protein structures of the silk fibers allowing for the proÂŹduction of synthetic silks.[2] This study compares the mid-infrared (Mid IR) spectra of silk from five different spider species to investigate the com-monalities between species and web type. The results demonstrate the Mid IR spectra from all types of spider silk to be similar, showing protein peaks in the Amide I and II regions. To study the environmental effects of the acid solution on the silk protein structure, two of the five speciesâ silk: Black & Yellow Orb Weaver (Argiope aurantia) and Black Widow (Latrodectus hesperus), were exposed to either rain water or 0.001 M sulphuric acid solution, similar to acid rain in pH. Spectra obtained at the Mid IR beamline and the data obtained from the X-ray Absorption Near Edge Spectroscopy (XANES) were compared for these samples to see the effect of the acid rain-like soluÂŹtion on the silk proteins. No conclusive evidence from the data is present to suggest that the acid rain solution had an effect on the protein structures of either type of spider silk.La soie dâaraignĂ©e est Ă la fois robuste et flexible pour sa taille et son poids.[1] Ces propriĂ©tĂ©s ont piquĂ© la curiositĂ© de dĂ©terminer la structure des protĂ©ines des fibres de soie qui pourrait permettre Ă©ventuelleÂŹment la production des soies synthĂ©tiques.[2] Cette Ă©tude compare les spectres mi- infrarouges (Mi IR) de soie de cinq espĂšces diffĂ©rentes dâaraignĂ©e afin de trouver des similitudes entre les espĂšces et les genres de toiles. Les rĂ©sultats dĂ©montrent que les spectres mi- infrarouges de tout type de soie dâaraignĂ©e Ă©tudiĂ© sont similaires, prĂ©sentant des apogĂ©es de protĂ©ines dans les rĂ©gions de lâAmide I et II. Afin dâĂ©tudier les effets environnementaux dâune solution acide sur la structure de la protĂ©ÂŹine de soie, la soie de deux des cinq espĂšces, le orbe tisserand noir et jaune (Argiope aurantia) et la veuve noire (Latrodectus Hesperus), ont Ă©tĂ© expoÂŹsĂ© soit Ă la pluie naturelle soit Ă une solution dâacide sulfurique 0.001 M qui est proche au pH de la pluie acide. Les spectres obtenus Ă lâonde dirigĂ©e Mi IR et les donnĂ©es obtenues de lâabsorption de la radiÂŹographie prĂšs du seuil de la spectroscopie (ARSS) ont Ă©tĂ© comparĂ©s de ces Ă©chantillons afin de conÂŹstater lâeffet de la solution dâacide sulfurique sur des protĂ©ines de soie. Il nây avait aucune preuve probante des donnĂ©es suggĂ©rant que la solution dâacide sulfurique avait un effet sur la structure des protĂ©ines de soie des araignĂ©es Ă©tudiĂ©
An international intercomparison of stable carbon isotope composition measurements of dissolved inorganic carbon in seawater
We report results of an intercomparison of stable carbon isotope ratio measurements in seawater dissolved inorganic carbon (ÎŽ 13CâDIC) which involved 16 participating laboratories from various parts of the world. The intercomparison involved distribution of samples of a Certified Reference Material for seawater DIC concentration and alkalinity and a preserved sample of deep seawater collected at 4000âm in the northeastern Atlantic Ocean. The betweenâlab standard deviation of reported uncorrected values measured with diverse analytical, detection, and calibration methods was 0.11â° (1Ï ). The multiâlab average ÎŽ 13CâDIC value reported for the deep seawater sample was consistent within 0.1â° with historical measured values for the same water mass. Application of a correction procedure based on a consensus value for the distributed reference material, improved the betweenâlab standard deviation to 0.06â°. The magnitude of the corrections were similar to those used to correct independent data sets using crossover comparisons, where deep water analyses from different cruises are compared at nearby locations. Our results demonstrate that the accuracy/uncertainty target proposed by the Global Ocean Observing System (±0.05â°) is attainable, but only if an aqueous phase reference material for ÎŽ 13CâDIC is made available and used by the measurement community. Our results imply that existing Certified Reference Materials used for seawater DIC and alkalinity quality control are suitable for this purpose, if a âCertifiedâ or internally consistent âconsensusâ value for ÎŽ 13CâDIC can be assigned to various batches.publishedVersio
Slip pulse and resonance of the Kathmandu basin during the 2015 Gorkha earthquake, Nepal.
This is the author accepted manuscript. The final version is available from AAAS via http://dx.doi.org/10.1126/science.aac6383Detailed geodetic imaging of earthquake ruptures enhances our understanding of earthquake physics and associated ground shaking. The 25 April 2015 moment magnitude 7.8 earthquake in Gorkha, Nepal was the first large continental megathrust rupture to have occurred beneath a high-rate (5-hertz) Global Positioning System (GPS) network. We used GPS and interferometric synthetic aperture radar data to model the earthquake rupture as a slip pulse ~20 kilometers in width, ~6 seconds in duration, and with a peak sliding velocity of 1.1 meters per second, which propagated toward the Kathmandu basin at ~3.3 kilometers per second over ~140 kilometers. The smooth slip onset, indicating a large (~5-meter) slip-weakening distance, caused moderate ground shaking at high frequencies (>1 hertz; peak ground acceleration, ~16% of Earth's gravity) and minimized damage to vernacular dwellings. Whole-basin resonance at a period of 4 to 5 seconds caused the collapse of tall structures, including cultural artifacts.The Nepal Geodetic Array was funded by internal funding to JPA from
Caltech and DASE and by the Gordon and Betty Moore Foundation, through Grant GBMF 423.01 to the Caltech Tectonics Observatory and was maintained thanks to NSF Grant EAR 13-5136. Andrew Miner and the PAcific Northwest Geodetic Array (PANGA) at Central Washington University are thanked for technical assistance with the construction and operation of the Tribhuvan University-CWU network. Additional funding for the TU-CWU network came from United Nations Development Programme and Nepal Academy for Science and Technology. The high rate data were recovered thanks to a rapid intervention funded by NASA (US) and the Department of Foreign International Development (UK). We thank Trimble Navigation Ltd and the Vaidya family for supporting the rapid response as well. The accelerometer record at KATNP was provided by USGS. Research at UC Berkeley was funded by the Gordon and Betty Moore Foundation through grant GBMF 3024. A portion of this work was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. The GPS data were processed by ARIA (JPL) and the Scripps Orbit and Permanent Array Center.
The effort at the Scripps Institution of Oceanography was funded by NASA grants NNX14AQ53G and NNX14AT33G. ALOS-2 data were provided under JAXA (Japan) PI Investigations 1148 and 1413. JPA thanks the Royal Society for support. We thank Susan Hough, Doug Given, Irving Flores and Jim Luetgert for contribution to the installation of this station
Dust in Hot Environments: Giant Dusty Galactic Halos
I review some of the evidences for dust in the Local Bubble and in galactic
halos and show that a general mechanism based on radiation pressure is capable
of evacuating dust grains from regions dominated by massive star energy input
and thus originate huge dusty halos. A Monte Carlo/particle model has been
developed to study the dust dynamics above HII chimneys and the results, among
other findings, show that dust can travel several kpc away from the plane of
the parent galaxy. The cosmological implications of extragalactic dust are
briefly outlined.Comment: 10 pages, LaTeX (lamuphys.sty), 3 figures, IAU166, The Local Bubble
and Beyond, Highlight Tal
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