30,746 research outputs found
SkyMapper and the Southern Sky Survey - a resource for the southern sky
SkyMapper is amongst the first of a new generation of dedicated, wide-field
survey telescopes. The 1.3m SkyMapper telescope features a 5.7 square degree
field-of-view Cassegrain imager and will see first light in late 2007. The
primary goal of the facility is to conduct the Southern Sky Survey a six
colour, six epoch survey of the southern sky. The survey will provide
photometry for objects between 8th and 23rd magnitude with global photometric
accuracy of 0.03 magnitudes and astrometry to 50 mas. This will represent a
valuable scientific resource for the southern sky and in addition provide a
basis for photometric and astrometric calibration of imaging data.Comment: 6 pages, 4 figures, proceedings of ESO Calibration Workshop 200
The origin of amorphous rims on lunar plagioclase grains: Solar wind damage or vapor condensates
A distinctive feature of micron sized plagioclase grains from mature lunar soils is a thin (20 to 100 nm) amorphous rim surrounding the grains. These rims were originally described from high voltage electron microscope observations of lunar plagioclase grains by Dran et al., who observed rims up to 100 nm thick on plagioclase grains from Apollo 11 and 12 soils. These rims are believed to be the product of solar wind damage. The amorphous rims were studied on micron sized plagioclase grains from a mature Apollo 16 soil using a JEOL 200FX transmission electron microscope equipped with an energy dispersive x ray spectrometer. It was found that the amorphous rims are compositionally distinct from the interior plagioclase and it is proposed that a major component of vapor condensates is present in the rims
Spin-Wave Lifetimes Throughout the Brillouin Zone
We use a neutron spin-echo method with eV resolution to determine the
lifetimes of spin waves in the prototypical antiferromagnet MnF over the
entire Brillouin zone. A theory based on the interaction of magnons with
longitudinal spin fluctuations provides an excellent, parameter-free
description of the data, except at the lowest momenta and temperatures. This is
surprising, given the prominence of alternative theories based on magnon-magnon
interactions in the literature. The results and technique open up a new avenue
for the investigation of fundamental concepts in magnetism. The technique also
allows measurement of the lifetimes of other elementary excitations (such as
lattice vibrations) throughout the Brillouin zone.Comment: 12 pages, 4 figure
Finding RR Lyrae Stars with SkyMapper: an Observational Test
One of the major science goals of the SkyMapper Survey of the Southern
Hemisphere sky is the determination of the shape and extent of the halo of the
Galaxy. In this paper we quantify the likely efficiency and completeness of the
survey as regards the detection of RR Lyrae variable stars, which are excellent
tracers of the halo stellar population. We have accomplished this via
observations of the RR Lyrae-rich globular cluster NGC 3201. We find that for
single epoch uvgri observations followed by two further epochs of g, r imaging,
as per the intended three-epoch survey strategy, we recover known RR Lyraes
with a completeness exceeding 90%. We also investigate boundaries in the
gravity-sensitive single-epoch two-color diagram that yield high completeness
and high efficiency (i.e., minimal contamination by non-RR Lyraes) and the
general usefulness of this diagram in separating populations.Comment: 10 pages, 5 figures, to appear in the Publications of the
Astronomical Society of Australia (PASA), published by Cambridge University
Pres
Red Giants in the Small Magellanic Cloud. II. Metallicity Gradient and Age-Metallicity Relation
We present results from the largest CaII triplet line metallicity study of
Small Magellanic Cloud (SMC) field red giant stars to date, involving 3037
objects spread across approximately 37.5 sq. deg., centred on this galaxy. We
find a median metallicity of [Fe/H]=-0.99+/-0.01, with clear evidence for an
abundance gradient of -0.075+/-0.011 dex / deg. over the inner 5 deg. We
interpret the abundance gradient to be the result of an increasing fraction of
young stars with decreasing galacto-centric radius, coupled with a uniform
global age-metallicity relation. We also demonstrate that the age-metallicity
relation for an intermediate age population located 10kpc in front of the NE of
the Cloud is indistinguishable from that of the main body of the galaxy,
supporting a prior conjecture that this is a stellar analogue of the Magellanic
Bridge. The metal poor and metal rich quartiles of our RGB star sample (with
complementary optical photometry from the Magellanic Clouds Photometric Survey)
are predominantly older and younger than approximately 6Gyr, respectively.
Consequently, we draw a link between a kinematical signature, tentatively
associated by us with a disk-like structure, and the upsurges in stellar
genesis imprinted on the star formation history of the central regions of the
SMC. We conclude that the increase in the star formation rate around 5-6Gyr ago
was most likely triggered by an interaction between the SMC and LMC.Comment: To appear in MNRA
Energy Gaps and Kohn Anomalies in Elemental Superconductors
The momentum and temperature dependence of the lifetimes of acoustic phonons
in the elemental superconductors Pb and Nb was determined by resonant spin-echo
spectroscopy with neutrons. In both elements, the superconducting energy gap
extracted from these measurements was found to converge with sharp anomalies
originating from Fermi-surface nesting (Kohn anomalies) at low temperatures.
The results indicate electron many-body correlations beyond the standard
theoretical framework for conventional superconductivity. A possible mechanism
is the interplay between superconductivity and spin- or charge-density-wave
fluctuations, which may induce dynamical nesting of the Fermi surface
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