5,702 research outputs found
Modelling Epsilon Aurigae without solid particles
Three components can be expected to contribute to the emission of epsilon Aurigae. There is a primary F star. There is an opaque disk which occults it, and there is a gas stream which is observed to produce absorption lines. Evidence that the disk is not responsible for the gas stream lines comes both from the radial velocities, which are too small, and from the IR energy distribution out of eclipse, which shows free-free emission that would produce inadequate optical depth in electron scattering. The color temperature of the IR excess can give misleading indications of low temperature material. Free-free emission at 10,000 K between 10 and 20 microns has a color temperature of 350 K. Attempts to mold the system are discussed
Development and Characterization of a Fast Neutron Imaging Telescope (FNIT) for 1--20 MeV Neutrons From the Sun and Nuclear Material
We discuss the development and complete characterization of a double scatter telescope for 1--20 MeV neutrons intended for applications in solar physics and nuclear security. In high-energy solar physics, detecting the presence of low energy accelerated ions in the low corona is recognized as an important goal. The surest indication of the acceleration of these particles is the detection of low energy (\u3c10 MeV) neutrons. These measurements can only be made in the inner heliosphere due to the finite neutron lifetime and flux divergence as they leave the Sun. Additionally, the field of nuclear security has interest in an instrument that can detect, measure, and locate sources of (\u3c10 MeV) neutrons from nuclear material. Materials of interest, namely uranium and transuranics, emit neutrons via spontaneous or induced fission. Unlike other neutral emission from nuclear material, (e.g. gamma rays), copious and penetrating neutron emission is unique to fissionable material.
The FNIT instrument was carefully tailored for both applications with a low energy threshold. A double scatter instrument allows for background rejection techniques to obtain increased sensitivity. A small, modular prototype instrument was constructed at UNH with laboratory calibration completed to tune the pulse height and shape, threshold, and time-of-flight for neutron measurements. Quasi-monoenergetic neutron beams calibrated the prototype over the full energy range and fission neutrons were used to test the response and performance of the instrument.
Simulations characterized the instrument energy response and were used to generate response matrices for data inversion. We used zeroth-order Tikhonov regularization de-convolution algorithms to obtain the true neutron source spectrum for a given regularization (smoothing) parameter, lambda. Independent of the binning strategy, lambda is of order 10-6. We find that lambda +/- sigma results in a 2% error in total neutron counts; an error within +/-5-sigma results in a variation of ≤ 30% in total neutron counts. Double scatter imaging, adopted from gamma-ray telescopes, demonstrate source location identification can be obtained. We apply laboratory and simulation information to obtain performance estimates of future instruments near the Sun and in the field
Temperature and gravity of the pulsating extreme helium star LSS 3184 (BX Cir) through its pulsation cycle
We report the analysis of optical spectra of the extreme helium star LSS 3184
(BX Cir) to determine its effective temperature and gravity throughout its
pulsation cycle. The spectra were also used to measure its chemical abundances.
We report rest gravity, log g = 3.38 +/- 0.02, and a chemical abundance
mixture consistent with those reported earlier in a study using an optical
spectrum with lower spectral resolution and a lower signal to noise ratio. Our
analysis decreases the upper limit for the H abundance to H < 6.0 (mass
fraction < 7.1 x 10^-7). Our gravity corresponds to stellar mass M = 0.47 +/-
0.03 M_sun.
We find that the effective log g varies through the pulsation cycle with an
amplitude of 0.28 dex. The effective gravity is smaller than the rest gravity
except when the star is very near its minimum radius. The change in effective
gravity is primarily caused by acceleration of the stellar surface.
Based on the optical spectra, we find the temperature varies with an
amplitude of 3450 K. We find a time averaged mean temperature, 23390 +/- 90 K,
consistent with that found in the earlier optical spectrum study. The mean
temperature is 1750 K hotter than that found using combined ultraviolet spectra
and V and R photometry and the variation amplitude is larger. This discrepancy
is similar to that found for the extreme helium star V652 Her.Comment: 7 pages, 6 figures, LaTeX, to be published in A&
The MultiSite Spectroscopic Telescope campaign: 2m spectroscopy of the V361 Hya variable PG1605+072
We present results and analysis for the 2m spectroscopic part of the
MultiSite Spectroscopic Telescope (MSST) campaign undertaken in May/June 2002.
The goal of the project was to observe the pulsating subdwarf B star PG1605+072
simultaneously in velocity and photometry and to resolve as many of the >50
known modes as possible, which will allow a detailed asteroseismological
analysis. We have obtained over 150 hours of spectroscopy, leading to an
unprecedented noise level of only 207m/s. We report here the detection of 20
frequencies in velocity, with two more likely just below our detection
threshold. In particular, we detect 6 linear combinations, making PG1605+072
only the second star known to show such frequencies in velocity. We investigate
the phases of these combinations and their parent modes and find relationships
between them that cannot be easily understood based on current theory. These
observations, when combined with our simultaneous photometry, should allow
asteroseismology of this most complicated of sdB pulsators.Comment: 9 pages, 5 figures, accepted for publication in A&A; Figure 1 at
lower resolution than accepted versio
Variability in the extreme helium star LSS 5121
We report a photometric and spectroscopic study of the hot extreme helium
star LSS 5121. We found photometric variability, but no period was evident in
its periodogram. This is consistent with the previous proposal, based on
spectral line variations, that LSS 5121 is a non-radial pulsator similar to
other hot extreme helium stars.Comment: 5 pages, 6 figure
Data specifications for INSPIRE
In Europe a major recent development has been the entering in force of the INSPIRE Directive in May 2007,
establishing an infrastructure for spatial information in Europe to support Community environmental policies, and
policies or activities which may have an impact on the environment.
INSPIRE is based on the infrastructures for spatial information established and operated by the 27 Member
States of the European Union. The Directive addresses 34 spatial data themes needed for environmental
applications, with key components specified through technical implementing rules. This makes INSPIRE a unique
example of a legislative ¿regional¿ approach.
One of the requirements of the INSPIRE Directive is to make existing spatial data sets with relevance for
one of the spatial data themes available in an interoperable way, i.e. where the spatial data from different sources
in Europe can be combined to a coherent result.
Since INSPIRE covers a wide range of spatial data themes, the first step has been the development of a
modelling framework that provides a common foundation for all themes. This framework is largely based on the
ISO 19100 series of standards. The use of common generic spatial modelling concepts across all themes is an
important enabler for interoperability.
As a second step, data specifications for the first set of themes has been developed based on the modelling
framework. The themes include addresses, transport networks, protected sites, hydrography, administrative areas
and others. The data specifications were developed by selected experts nominated by stakeholders from all over
Europe. For each theme a working group was established in early 2008 working on their specific theme and
collaborating with the other working groups on cross-theme issues. After a public review of the draft specifications
starting in December 2008, an open testing process and thorough comment resolution process, the draft
technical implementing rules for these themes have been approved by the INSPIRE Committee. After they enter
into force they become part of the legal framework and European Member States have to implement these rules.
The next step is the development of the remaining 25 spatial data themes, which include many themes of
interest for the Earth Sciences including geology, meteorological and oceanographic geographic features, atmospheric
conditions, habitats and biotopes, species distribution, environmental monitoring facilities, and land cover
to name a few. The process will follow in general the same steps as for the first themes and the working groups are
expected to start their work in March/April 2010. The first draft specifications for public comment are expected at
the end of 2010 and the work is scheduled to be completed in 2012.JRC.DDG.H.6-Spatial data infrastructure
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