158 research outputs found
Improvement of a Low-cost DIY Wave Gauge
The impacts of waves on shorelines and nearshore ecosystems has highlighted the need for extension and other environmental professionals to have access to accurate and affordable wave measurements. The development of a low-cost DIY wave gauge improved the accessibility of these measurements; however, the original design was limited in battery life. Here, an improved version of the low-cost DIY wave gauge, the DIY Feather Wave Gauge, is presented with the same performance, longer battery life, smaller design, and cheaper cost along with tutorials, parts lists, and other resources. This new gauge has been used to improve shoreline management recommendations
Optical and Radio Polarimetry of the M87 Jet at 0.2" Resolution
We discuss optical (HST/WFPC2 F555W) and radio (15 GHz VLA) polarimetry
observations of the M87 jet taken during 1994-1995. Many knot regions are very
highly polarized (, approaching the theoretical maximum for
optically thin synchrotron radiation), suggesting highly ordered magnetic
fields. High degrees of polarization are also observed in interknot regions.
While the optical and radio polarization maps share many similarities, we
observe significant differences between the radio and optical polarized
structures, particularly for bright knots in the inner jet, giving us important
insight into the jet's radial structure. Unlike in the radio, the optical
magnetic field position angle becomes perpendicular to the jet at the upstream
ends of knots HST-1, D, E and F. Moreover, the optical polarization decreases
markedly at the position of the flux maxima in these knots. In contrast, the
magnetic field position angle observed in the radio remains parallel to the jet
in most of these regions, and the decreases in radio polarization are smaller.
More minor differences are seen in other jet regions. Many of the differences
between optical and radio polarimetry results can be explained in terms of a
model whereby shocks occur in the jet interior, where higher-energy electrons
are concentrated and dominate both polarized and unpolarized emissions in the
optical, while the radio maps show strong contributions from lower-energy
electrons in regions with {\bf B} parallel, near the jet surface.Comment: 28 pages, 7 figures; accepted for publication in AJ (May 1999
Polarimetry and the High-Energy Emission Mechanisms in Quasar Jets. The Case of PKS 1136-135
Since the discovery of kiloparsec-scale X-ray emission from quasar jets, the
physical processes responsible for their high-energy emission have been poorly
defined. A number of mechanisms are under active debate, including synchrotron
radiation, inverse-Comptonized CMB (IC/CMB) emission, and other Comptonization
processes. In a number of cases, the optical and X-ray emission of jet regions
are inked by a single spectral component, and in those, high- resolution
multi-band imaging and polarimetry can be combined to yield a powerful
diagnostic of jet emission processes. Here we report on deep imaging photometry
of the jet of PKS 1136135 obtained with the {\it Hubble Space Telescope.} We
find that several knots are highly polarized in the optical, with fractional
polarization . When combined with the broadband spectral shape
observed in these regions, this is very difficult to explain via IC/CMB models,
unless the scattering particles are at the lowest-energy tip of the electron
energy distribution, with Lorentz factor , and the jet is also
very highly beamed () and viewed within a few degrees of the
line of sight. We discuss both the IC/CMB and synchrotron interpretation of the
X-ray emission in the light of this new evidence, presenting new models of the
spectral energy distribution and also the matter content of this jet. The high
polarizations do not completely rule out the possibility of IC/CMB
optical-to-X-ray emission in this jet, but they do strongly disfavor the model.
We discuss the implications of this finding, and also the prospects for future
work.Comment: 14 pages, 8 figures, ApJ in pres
An optical-IR jet in 3C133
We report the discovery of a new optical-IR synchrotron jet in the radio
galaxy 3C133 from our HST/NICMOS snapshot survey. The jet and eastern hotspot
are well resolved, and visible at both optical and IR wavelengths. The IR jet
follows the morphology of the inner part of the radio jet, with three distinct
knots identified with features in the radio. The radio-IR SED's of the knots
are examined, along with those of two more distant hotspots at the eastern
extreme of the radio feature. The detected emission appears to be synchrotron,
with peaks in the NIR for all except one case, which exhibits a power-law
spectrum throughout.Comment: ApJ accepted. 14 pages, 6 figure
O/IR Polarimetry for the 2010 Decade (GAN): Science at the Edge, Sharp Tools for All
Science opportunities and recommendations concerning optical/infrared
polarimetry for the upcoming decade in the field of Galactic science.
Community-based White Paper to Astro2010 in response to the call for such
papers.Comment: White Paper to the Galactic Neighborhood (GAN) Science Frontiers
Panel of the Astro2010 Decadal Surve
Heterogeneous N2O5 Uptake During Winter: Aircraft Measurements During the 2015 WINTER Campaign and Critical Evaluation of Current Parameterizations
Nocturnal dinitrogen pentoxide (N2O5) heterogeneous chemistry impacts regional air quality and the distribution and lifetime of tropospheric oxidants. Formed from the oxidation of nitrogen oxides, N2O5 is heterogeneously lost to aerosol with a highly variable reaction probability, γ(N2O5), dependent on aerosol composition and ambient conditions. Reaction products include soluble nitrate (HNO3 or NO3−) and nitryl chloride (ClNO2). We report the first‐ever derivations of γ(N2O5) from ambient wintertime aircraft measurements in the critically important nocturnal residual boundary layer. Box modeling of the 2015 Wintertime INvestigation of Transport, Emissions, and Reactivity (WINTER) campaign over the eastern United States derived 2,876 individual γ(N2O5) values with a median value of 0.0143 and range of 2 × 10−5 to 0.1751. WINTER γ(N2O5) values exhibited the strongest correlation with aerosol water content, but weak correlations with other variables, such as aerosol nitrate and organics, suggesting a complex, nonlinear dependence on multiple factors, or an additional dependence on a nonobserved factor. This factor may be related to aerosol phase, morphology (i.e., core shell), or mixing state, none of which are commonly measured during aircraft field studies. Despite general agreement with previous laboratory observations, comparison of WINTER data with 14 literature parameterizations (used to predict γ(N2O5) in chemical transport models) confirms that none of the current methods reproduce the full range of γ(N2O5) values. Nine reproduce the WINTER median within a factor of 2. Presented here is the first field‐based, empirical parameterization of γ(N2O5), fit to WINTER data, based on the functional form of previous parameterizations
The Optical-Near-IR Spectrum of the M87 Jet From HST Observations
We present 1998 HST observations of M87 which yield the first single-epoch
optical and radio-optical spectral index images of the jet at
resolution. We find , comparable to previous
measurements, and (),
slightly flatter than previous workers. Reasons for this discrepancy are
discussed. These observations reveal a large variety of spectral slopes. Bright
knots exhibit flatter spectra than interknot regions. The flattest spectra
(; comparable to or flatter than ) are
found in two inner jet knots (D-East and HST-1) which contain the fastest
superluminal components. In knots A, B and C, and are
essentially anti-correlated. Near the flux maxima of knots HST-1 and F, changes
in lag changes in , but in knots D and E, the opposite
relationship is observed. This is further evidence that radio and optical
emissions in the M87 jet come from substantially different physical regions.
The delays observed in the inner jet are consistent with localized particle
acceleration, with for optically emitting electrons in
knots HST-1 and F, and for optically emitting electrons
in knots D and E. Synchrotron models yield \nu_B \gsim 10^{16} Hz for knots
D, A and B, and somewhat lower values, Hz, in
other regions. If X-ray emissions from knots A, B and D are co-spatial with
optical and radio emission, we can strongly rule out the ``continuous
injection'' model. Because of the short lifetimes of X-ray synchrotron emitting
particles, the X-ray emission likely fills volumes much smaller than the
optical emission regions.Comment: Text 17 pages, 3 Tables, 11 figures, accepted by Ap
Morphology and kinematics of the ionised gas in early-type galaxies
We present results of our ongoing study of the morphology and kinematics of
the ionised gas in 48 representative nearby elliptical and lenticular galaxies
using the SAURON integral-field spectrograph on the 4.2m William Herschel
Telescope. Making use of a recently developed technique, emission is detected
in 75% of the galaxies. The ionised-gas distributions display varied
morphologies, ranging from regular gas disks to filamentary structures.
Additionally, the emission-line kinematic maps show, in general, regular
motions with smooth variations in kinematic position angle. In most of the
galaxies, the ionised-gas kinematics is decoupled from the stellar counterpart,
but only some of them present signatures of recent accretion of gaseous
material. The presence of dust is very common in our sample and is usually
accompanied by gas emission. Our analysis of the [OIII]/Hbeta emission-line
ratios, both across the whole sample as well as within the individual galaxies,
suggests that there is no unique mechanism triggering the ionisation of the
gas.Comment: 8 pages, 2 figures, submitted to "Adaptive Optics-Assisted
Integral-Field Spectroscopy", Rutten R.G.M., Benn C.R., Mendez J., eds., May
2005, La Palma (Spain), New Astr. Rev. For full resolution PS, see
http://www.strw.leidenuniv.nl/~jfalcon/JFB_AOmeeting_color_hires.ps.g
The infrared-dominated jet of 3C401
We present a Hubble Space Telescope image of the FRII radio galaxy 3C 401,
obtained at 1.6 microns with the NICMOS camera in which we identify the
infrared counterpart of the brightest region of the radio jet. The jet has a
complex radio structure and brightens where bending occurs, most likely as a
result of relativistic beaming. We analyze archival data in the radio, optical
and X-ray bands and we derive its spectral energy distribution. Differently
from all of the previously known optical extragalactic jets, the jet in 3C401
is not detected in the X-rays even in a long 48ksec X-ray Chandra exposure and
the infrared emission dominates the overall SED. We propose that the dominant
radiation mechanism of this jet is synchrotron. The low X-ray emission is then
caused by two different effects: i) the lack of any strong external photon
field and ii) the shape of the electron distribution. This affects the location
of the synchrotron peak in the SED, resulting in a sharp cut-off at energies
lower than the X-rays. Thus 3C401 shows a new type of jet which has
intermediate spectral properties between those of FRI, which are dominated by
synchrotron emission up to X-ray energies, and FRII/QSO, which show a strong
high-energy emission due to inverse-Compton scattering of external photons.
This might be a clue for the presence of a continuous ``sequence'' in the
properties of large scale jets, in analogy with the ``blazar sequence'' already
proposed for sub-pc scale jets.Comment: 7 pages, 5 figures, accepted for publication in the ApJ. A typo in
the value of the radio to X-ray spectral index (sect. 5, paragraph 2, thanks
to T. Cheung) and other minor corrections have been mad
Large-Scale Variation in Wave Attenuation of Oyster Reef Living Shorelines and the Influence of Inundation Duration
One of the paramount goals of oyster reef living shorelines is to achieve sustained and adaptive coastal protection, which requires meeting ecological (i.e., develop a self-sustaining oyster population) and engineering (i.e., provide coastal defense) targets. In a large-scale comparison along the Atlantic and Gulf coasts of the United States, the efficacy of various designs of oyster reef living shorelines at providing wave attenuation was evaluated accounting for the ecological limitations of oysters with regards to inundation duration. A critical threshold for intertidal oyster reef establishment is 50% inundation duration. Living shorelines that spent less than half of the time (\u3c 50%) inundated were not considered suitable habitat for oysters, however, were effective at wave attenuation (68% reduction in wave height). Reefs that experienced \u3e 50% inundation were considered suitable habitat for oysters, but wave attenuation was similar to controls (no reef; ~5% reduction in wave height). Many of the oyster reef living shoreline approaches therefore failed to optimize the ecological and engineering goals. In both inundation regimes, wave transmission decreased with an increasing freeboard (difference between reef crest elevation and water level), supporting its importance in the wave attenuation capacity of oyster reef living shorelines. However, given that the reef crest elevation (and thus freeboard) should be determined by the inundation duration requirements of oysters, research needs to be re-focused on understanding the implications of other reef parameters (e.g. width) for optimising wave attenuation. A broader understanding of the reef characteristics and seascape contexts that result in effective coastal defense by oyster reefs is needed to inform appropriate design and implementation of oyster-based living shorelines globally
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