23,716 research outputs found
Search for the magnetic field of the O7.5 III star xi Persei
Cyclical wind variability is an ubiquitous but as yet unexplained feature
among OB stars. The O7.5 III(n)((f)) star xi Persei is the brightest
representative of this class on the Northern hemisphere. As its prominent
cyclical wind properties vary on a rotational time scale (2 or 4 days) the star
has been already for a long time a serious magnetic candidate. As the cause of
this enigmatic behavior non-radial pulsations and/or a surface magnetic field
are suggested. We present a preliminary report on our attempts to detect a
magnetic field in this star with high-resolution measurements obtained with the
spectropolarimeter Narval at TBL, France during 2 observing runs of 5 nights in
2006 and 5 nights in 2007. Only upper limits could be obtained, even with the
longest possible exposure times. If the star hosts a magnetic field, its
surface strength should be less than about 300 G. This would still be enough to
disturb the stellar wind significantly. From our new data it seems that the
amplitude of the known non-radial pulsations has changed within less than a
year, which needs further investigation.Comment: 2 pages, 6 figures, contributed poster at IAU Symposium 259 "Cosmic
Magnetic Fields: from Planets, to Stars and Galaxies", Tenerife, Spain,
November 3-7, 200
A holistic approach to the evaluation of sustainable housing
Residential housing is often evaluated against single or at best a limited number of similar criteria. These include quantifiable indicators such as energy use and its associated greenhouse gas emissions. It might also include material consumption from an embodied energy or resource use perspective. Social factors or qualitative indicators may be evaluated but are rarely placed or juxtaposed alongside these quantifiable indicators. A one-dimensional approach will be limiting because sustainable development includes both environmental and social factors. This paper describes the methodologies that have been developed to assess housing developments against five quite different criteria. These are: energy use, resource use, neighbourhood character, neighbourhood connectedness and diversity. In each case, high and low sustainability practice has been identified so that ranking is possible. These methodologies have then been tested by evaluating a typical precinct (approximately 400 m by 400 m) of a 1970-80s housing development in a suburb of Geelong. The rankings of the particular precinct have then been combined in a visual way to assist in the evaluation of the housing in a more holistic way. The results of this evaluation method are presented, along with a discussion of the strengths and weaknesses of the methodologies. The research is the outcome of collaboration by a cross-disciplinary group of academics within Deakin’s School of Architecture and Building
The Central Region in M100: Observations and Modeling
We present new high-resolution observations of the center of the late-type
spiral M100 (NGC 4321) supplemented by 3D numerical modeling of stellar and gas
dynamics, including star formation (SF). NIR imaging has revealed a stellar
bar, previously inferred from optical and 21 cm observations, and an
ovally-shaped ring-like structure in the plane of the disk. The K isophotes
become progressively elongated and skewed to the position angle of the bar
(outside and inside the `ring') forming an inner bar-like region. The galaxy
exhibits a circumnuclear starburst in the inner part of the K `ring'. Two
maxima of the K emission have been observed to lie symmetrically with respect
to the nucleus and equidistant from it slightly leading the stellar bar. We
interpret the twists in the K isophotes as being indicative of the presence of
a double inner Lindblad resonance (ILR) and test this hypothesis by modeling
the gas flow in a self-consistent gas + stars disk embedded in a halo, with an
overall NGC4321-like mass distribution. We have reproduced the basic morphology
of the region (the bar, the large scale trailing shocks, two symmetric K peaks
corresponding to gas compression maxima which lie at the caustic formed by the
interaction of a pair of trailing and leading shocks in the vicinity of the
inner ILR, both peaks being sites of SF, and two additional zones of SF
corresponding to the gas compression maxima, referred usually as `twin peaks').Comment: 31 pages, postscript, compressed, uuencoded. 21 figures available in
postscript, compressed form by anonymous ftp from
ftp://asta.pa.uky.edu/shlosman/main100 , mget *.ps.Z. To appear in Ap.
VLT/VIMOS Observations of an Occulting Galaxy Pair: Redshifts and Effective Extinction Curve
We present VLT/VIMOS IFU observations of an occulting galaxy pair previously
discovered in HST observations. The foreground galaxy is a low-inclination
spiral disk, which causes clear attenuation features seen against the bright
bulge and disk of the background galaxy. We find redshifts of and z=0.065 for the foreground and background galaxy respectively.
This relatively small difference does not rule out gravitational interaction
between the two galaxies. Emission line ratios point to a star-forming, not
AGN-dominated foreground galaxy.
We fit the Cardelli, Clayton & Mathis (CCM) extinction law to the spectra of
individual fibres to derive slope () and normalization (). The
normalization agrees with the HST attenuation map and the slope is lower than
the Milky Way relation (), which is likely linked to the spatial
sampling of the disk. We speculate that the values of point to either
coherent ISM structures in the disk larger than usual ( kpc) or higher
starting values of , indicative of recent processing of the dust.
The foreground galaxy is a low stellar mass spiral () with a high dust content (). The dust disk geometry visible in the HST image would explain the
observed SED properties of smaller galaxies: a lower mean dust temperature, a
high dust-to-stellar mass ratio but relatively little optical attenuation.
Ongoing efforts to find occulting pairs with a small foreground galaxies will
show how common this geometry is.Comment: 16 pages, 3 tables, 13 figures, accepted for publication in MNRA
The cleavage surface of the BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) superconductors: from diversity to simplicity
We elucidate the termination surface of cleaved single crystals of the
BaFe_(2-x)Co_(x)As_(2) and Fe_(y)Se_(1-x)Te_(x) families of the high
temperature iron based superconductors. By combining scanning tunneling
microscopic data with low energy electron diffraction we prove that the
termination layer of the Ba122 systems is a remnant of the Ba layer, which
exhibits a complex diversity of ordered and disordered structures. The observed
surface topographies and their accompanying superstructure reflections in
electron diffraction depend on the cleavage temperature. In stark contrast,
Fe_(y)Se_(1-x)Te_(x) possesses only a single termination structure - that of
the tetragonally ordered Se_(1-x)Te_(x) layer.Comment: 4 pages, 4 figure
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