303 research outputs found
Managing Research Data: Gravitational Waves
The project which led to this report was funded by JISC in 2010–2011 as part of its
‘Managing Research Data’ programme, to examine the way in which Big Science data
is managed, and produce any recommendations which may be appropriate.
Big science data is different: it comes in large volumes, and it is shared and
exploited in ways which may differ from other disciplines. This project has explored
these differences using as a case-study Gravitational Wave data generated by the LSC,
and has produced recommendations intended to be useful variously to JISC, the funding
council (STFC) and the LSC community.
In Sect. 1 we define what we mean by ‘big science’, describe the overall data
culture there, laying stress on how it necessarily or contingently differs from other
disciplines.
In Sect. 2 we discuss the benefits of a formal data-preservation strategy, and the
cases for open data and for well-preserved data that follow from that. This leads to our
recommendations that, in essence, funders should adopt rather light-touch prescriptions
regarding data preservation planning: normal data management practice, in the areas
under study, corresponds to notably good practice in most other areas, so that the only
change we suggest is to make this planning more formal, which makes it more easily
auditable, and more amenable to constructive criticism.
In Sect. 3 we briefly discuss the LIGO data management plan, and pull together
whatever information is available on the estimation of digital preservation costs.
The report is informed, throughout, by the OAIS reference model for an open
archive. Some of the report’s findings and conclusions were summarised in [1].
See the document history on page 37
Baade's red sheet resolved into stars with HST in the Blue Compact Dwarf Galaxy VII Zw 403
HST WFPC2 observations of the nearby Blue Compact Dwarf Galaxy VII~Zw~403 (=
UGC 6456) resolve single stars down to M-2.5, deep enough to
identify red giants. This population has a more uniform spatial distribution
than the young main-sequence stars and supergiants, forming the structure known
as "Baade's red sheet". We conclude that VII~Zw~403 is not a primeval galaxy.Comment: submitted to: ApJ Letter
Utilization of photon orbital angular momentum in the low-frequency radio domain
We show numerically that vector antenna arrays can generate radio beams which
exhibit spin and orbital angular momentum characteristics similar to those of
helical Laguerre-Gauss laser beams in paraxial optics. For low frequencies (< 1
GHz), digital techniques can be used to coherently measure the instantaneous,
local field vectors and to manipulate them in software. This opens up for new
types of experiments that go beyond those currently possible to perform in
optics, for information-rich radio physics applications such as radio
astronomy, and for novel wireless communication concepts.Comment: 4 pages, 5 figures. Changed title, identical to the paper published
in PR
The LOFAR ling baseline snapshot calibrator survey
Aims:\ud
An efficient means of locating calibrator sources for international LOw Frequency ARray (LOFAR) is developed and used to determine the average density of usable calibrator sources on the sky for subarcsecond observations at 140 MHz.\ud
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Methods\ud
We used the multi-beaming capability of LOFAR to conduct a fast and computationally inexpensive survey with the full international LOFAR array. Sources were preselected on the basis of 325 MHz arcminute-scale flux density using existing catalogues. By observing 30 different sources in each of the 12 sets of pointings per hour, we were able to inspect 630 sources in two hours to determine if they possess a sufficiently bright compact component to be usable as LOFAR delay calibrators.\ud
\ud
Results:\ud
More than 40% of the observed sources are detected on multiple baselines between international stations and 86 are classified as satisfactory calibrators. We show that a flat low-frequency spectrum (from 74 to 325 MHz) is the best predictor of compactness at 140 MHz. We extrapolate from our sample to show that the sky density of calibrators that are sufficiently bright to calibrate dispersive and non-dispersive delays for the international LOFAR using existing methods is 1.0 per square degree.\ud
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Conclusions:\ud
The observed density of satisfactory delay calibrator sources means that observations with international LOFAR should be possible at virtually any point in the sky provided that a fast and efficient search, using the methodology described here, is conducted prior to the observation to identify the best calibrator
A Kinematic Link between Boxy Bulges, Stellar Bars, and Nuclear Activity in NGC 3079 & NGC 4388
We present direct kinematic evidence for bar streaming motions in two active
galaxies with boxy stellar bulges. The Hawaii Imaging Fabry-Perot
Interferometer was used on the Canada-France-Hawaii 3.6-m telescope and the
University of Hawaii 2.2-m telescope to derive the two-dimensional velocity
field of the line-emitting gas in the disks of the Sc galaxy NGC 3079 and the
Sb galaxy NGC 4388. In contrast to previous work based on long-slit data, the
detection of the bar potential from the Fabry-Perot data does not rely on the
existence of inner Lindblad resonances or strong bar-induced shocks. Simple
kinematic models which approximate the intrinsic gas orbits as nonintersecting,
inclined elliptical annuli that conserve angular momentum characterize the
observed velocity fields. Box-shaped bulges in both NGC 3079 and NGC 4388 are
confirmed using new near-infrared images to reduce dust obscuration.
Morphological analysis of starlight in these galaxies is combined with the gas
kinematics derived from the Fabry-Perot spectra to test evolutionary models of
stellar bars that involve transitory boxy bulges, and to quantify the
importance of such bars in fueling active nuclei. Our data support the
evolutionary bar models, but fail to prove convincingly that the stellar bars
in NGC 3079 and NGC 4388 directly trigger or sustain the nuclear activity.
(abridged)Comment: 31 pages, 18 figures, Latex, requires aaspp4.sty. Accepted for the
Astronomical Journal (November issue
Constraining the magnetic field geometry of the millisecond pulsar PSRJ0030+0451 from joint radio, thermal X-ray, and γ-ray emission
Context. With the advent of multi-wavelength electromagnetic observations of neutron stars - spanning many decades in photon energies - from radio wavelengths up to X-rays and γ-rays, it has become possible to significantly constrain the geometry and the location of the associated emission regions. Aims. In this work, we use results from the modelling of thermal X-ray observations of PSR J0030+0451 from the Neutron Star Interior Composition Explorer (NICER) mission and phase-aligned radio and γ-ray pulse profiles to constrain the geometry of an off-centred dipole that is able to reproduce the light curves in these respective bands simultaneously. Methods. To this aim, we deduced a configuration with a simple dipole off-centred from the location of the centre of the thermal X-ray hot spots. We show that the geometry is compatible with independent constraints from radio and -ray pulsations only, leading to a fixed magnetic obliquity of α ≈ 75° and a line-of-sight inclination angle of ζ ≈ 54°. Results. We demonstrate that an off-centred dipole cannot be rejected by accounting for the thermal X-ray pulse profiles. Moreover, the crescent shape of one spot is interpreted as the consequence of a small-scale surface dipole on top of the large-scale off-centred dipole
The Recent Evolution of the Dwarf Starburst Galaxy NGC 625 from Hubble Space Telescope Imaging
New HST/WFPC2 imaging of the dwarf starburst galaxy NGC 625 is presented.
These data, 80% complete to V and I magnitudes of 26.0 and 25.3, respectively,
allow us to study the recent star formation history of NGC 625. We derive a tip
of the red giant branch (TRGB) distance modulus of 27.95+/-0.07, corresponding
to a distance of 3.89+/-0.22 Mpc, and a location on the far side of the
Sculptor Group. NGC 625 has a well-defined radial stellar population gradient,
evidenced by a central concentration of young MS stars and an RGB/AGB ratio
that increases with galactocentric distance. The prominent AGB is very red, and
RGB stars are detected far from the central star forming regions. Using H Alpha
and H Beta narrow band imaging and previous optical spectroscopy we identify
substantial and varying internal extinction (A_V = 0.0 to 0.6 mag) associated
with the central active star formation regions. To better understand the
effects of internal extinction on the analysis of young stellar populations,
synthetic models are presented which, for the first time, examine and account
for this effect. Using the luminous blue helium burning stars, we construct a
simple model of the recent (< 100 Myr) star formation in which an elevated but
declining star formation rate has been present over this entire period. This is
at odds with the presence of spectroscopic W-R features in the major star
formation region which imply a short duration (<= 5 Myr) for the recent
starburst. This suggests that starbursts displaying W-R features are not
necessarily all of a short duration. Finally, we speculate on the possible
causes of the present burst of star formation in this apparently isolated
galaxy, and compare it to other nearby, well-studied dwarf starburst systems.Comment: 56 pages, including 15 figures (2 in color). Scheduled to appear in
AJ, December, 2003. Full-resolution version may be obtained at
http://www.astro.umn.edu/~Cannon/n625.p
Jordan-Schwinger map, 3D harmonic oscillator constants of motion, and classical and quantum parameters characterizing electromagnetic wave polarization
In this work we introduce a generalization of the Jauch and Rohrlich quantum
Stokes operators when the arrival direction from the source is unknown {\it a
priori}. We define the generalized Stokes operators as the Jordan-Schwinger map
of a triplet of harmonic oscillators with the Gell-Mann and Ne'eman SU(3)
symmetry group matrices. We show that the elements of the Jordan-Schwinger map
are the constants of motion of the three-dimensional isotropic harmonic
oscillator. Also, we show that generalized Stokes Operators together with the
Gell-Mann and Ne'eman matrices may be used to expand the polarization density
matrix. By taking the expectation value of the Stokes operators in a three-mode
coherent state of the electromagnetic field, we obtain the corresponding
generalized classical Stokes parameters. Finally, by means of the constants of
motion of the classical three-dimensional isotropic harmonic oscillator we
describe the geometric properties of the polarization ellips
First results of electric field and density observations by Cluster EFW based on initial months of operation
International audienceHighlights are presented from studies of the electric field data from various regions along the Cluster orbit. They all point towards a very high coherence for phenomena recorded on four spacecraft that are separated by a few hundred kilometers for structures over the whole range of apparent frequencies from 1 mHz to 9 kHz. This presents completely new opportunities to study spatial-temporal plasma phenomena from the magnetosphere out to the solar wind. A new probe environment was constructed for the CLUSTER electric field experiment that now produces data of unprecedented quality. Determination of plasma flow in the solar wind is an example of the capability of the instrument
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