23,237 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
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
Emergency conflict-related psychosocial interventions in Sierra Leone and Uganda: lessons from Médecins Sans Frontières
Médecins Sans Frontières has been involved in emergency mental health or psychosocial programmes since 1990. In this article the intervention model developed for emergency settings is shared. Psychosocial programmes distinguish two elements. The 'psycho'-component facilitates the reconnection of the affected individual to his environment. The 'socio'-element aims to create an environment that facilitates the individual to re-integrate. The nature of mental health and psychosocial programmes requires a multidisciplinary approach. Emotional support can also be provided by regular medical staff and does not always require a specialist. The years ahead of us are important for the development of psychosocial interventions. Fundamental issues such as programme evaluation need systematic research
Morphological Evolution of Distant Galaxies from Adaptive Optics Imaging
We report here on a sample of resolved, infrared images of galaxies at z~0.5
taken with the 10-m Keck Telescope's Adaptive Optics (AO) system. We regularly
achieve a spatial resolution of 0.05'' and are thus able to resolve both the
disk and bulge components. We have extracted morphological information for ten
galaxies and compared their properties to those of a local sample. The
selection effects of both samples were explicitly taken into account in order
to derive the unbiased result that disks at z~0.5 are ~0.6 mag arcsec^-2
brighter than, and about the same size as, local disks. The
no-luminosity-evolution case is ruled out at 90% confidence. We also find, in a
more qualitative analysis, that the bulges of these galaxies have undergone a
smaller amount of surface brightness evolution and have also not changed
significantly in size from z~0.5 to today. This is the first time this type of
morphological evolution has been measured in the infrared and it points to the
unique power of AO in exploring galaxy evolution.Comment: 27 pages, 7figures, 2 tables. Accepted for publication in the
Astrophysical Journa
Evolution in the Dust Lane Fraction of Edge-on L* Spiral Galaxies since z=0.8
The presence of a well-defined and narrow dust lane in an edge-on spiral
galaxy is the observational signature of a thin and dense molecular disk, in
which gravitational collapse has overcome turbulence. Using a sample of
galaxies out to z~1 extracted from the COSMOS survey, we identify the fraction
of massive disks that display a dust lane. Our goal is to explore the evolution
in the stability of the molecular ISM disks in spiral galaxies over a cosmic
timescale. We check the reliability of our morphological classifications
against changes in restframe wavelength, resolution, and cosmic dimming with
(artificially redshifted) images of local galaxies from SDSS. We find that the
fraction of L* disks with dust lanes in COSMOS is consistent with the local
fraction (~80%) out to z~0.7. At z=0.8, the dust lane fraction is only slightly
lower. A somewhat lower dust lane fraction in starbursting galaxies tentatively
supports the notion that a high specific star formation rate can efficiently
destroy or inhibit a dense molecular disk. A small subsample of higher redshift
COSMOS galaxies display low internal reddening (E[B-V]), as well as a low
incidence of dust lanes. These may be disks in which the growth of the dusty
ISM disk lags behind that of the stellar disk. We note that at z=0.8, the most
massive galaxies display a lower dust lane fraction than lower mass galaxies. A
small contribution of recent mergers or starbursts to this most massive
population may be responsible. The fact that the fraction of galaxies with dust
lanes in COSMOS is consistent with little or no evolution implies that models
to explain the Spectral Energy Distribution or the host galaxy dust extinction
of supernovae based on local galaxies are still applicable to higher redshift
spirals. It also suggests that dust lanes are long lived phenomena or can be
reformed over very short time-scales.Comment: 14 pages, 9 figures, 2 tables, accepted for publication by Ap
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
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