3,914 research outputs found
The Monitoring and Assessment Plan (MAP) Greater Everglades Wetlands Module- Landscape Pattern- Ridge, Slough, and Tree Island Mosaics: Year 1 Annual Report
In the current managed Everglades system, the pre-drainage, patterned mosaic of sawgrass ridges, sloughs and tree islands has been substantially altered or reduced largely as a result of human alterations to historic ecological and hydrological processes that sustained landscape patterns. The pre-compartmentalization ridge and slough landscape was a mosaic of sloughs, elongated sawgrass ridges (50-200m wide), and tree islands. The ridges and sloughs and tree islands were elongated in the direction of the water flow, with roughly equal area of ridge and slough. Over the past decades, the ridge-slough topographic relief and spatial patterning have degraded in many areas of the Everglades. Nutrient enriched areas have become dominated by Typha with little topographic relief; areas of reduced flow have lost the elongated ridge-slough topography; and ponded areas with excessively long hydroperiods have experienced a decline in ridge prevalence and shape, and in the number of tree islands (Sklar et al. 2004, Ogden 2005)
The early spectral evolution of SN 2004dt
Aims. We study the optical spectroscopic properties of Type Ia Supernova (SN
Ia) 2004dt, focusing our attention on the early epochs.
Methods. Observation triggered soon after the SN 2004dt discovery allowed us
to obtain a spectrophotometric coverage from day -10 to almost one year (~353
days) after the B band maximum. Observations carried out on an almost daily
basis allowed us a good sampling of the fast spectroscopic evolution of SN
2004dt in the early stages. To obtain this result, low-resolution, long-slit
spectroscopy was obtained using a number of facilities.
Results. This supernova, which in some absorption lines of its early spectra
showed the highest degree of polarization ever measured in any SN Ia, has a
complex velocity structure in the outer layers of its ejecta. Unburnt oxygen is
present, moving at velocities as high as ~16,700 km/s, with some
intermediate-mass elements (Mg, Si, Ca) moving equally fast. Modeling of the
spectra based on standard density profiles of the ejecta fails to reproduce the
observed features, whereas enhancing the density of outer layers significantly
improves the fit. Our analysis indicates the presence of clumps of
high-velocity, intermediate-mass elements in the outermost layers, which is
also suggested by the spectropolarimetric data.Comment: 13 pages, 15 figures, accepted for pubblication in Astronomy and
Astrophysic
Discovery of the progenitor of the type Ia supernova 2007on
Type Ia supernovae are exploding stars that are used to measure the
accelerated expansion of the Universe and are responsible for most of the iron
ever produced. Although there is general agreement that the exploding star is a
white dwarf in a binary system, the exact configuration and trigger of the
explosion is unclear, which could hamper their use for precision cosmology. Two
families of progenitor models have been proposed. In the first, a white dwarf
accretes material from a companion until it exceeds the Chandrasekhar mass,
collapses and explodes. Alternatively, two white dwarfs merge, again causing
catastrophic collapse and an explosion. It has hitherto been impossible to
determine if either model is correct. Here we report the discovery of an object
in pre-supernova archival X-ray images at the position of the recent type Ia
supernova (2007on) in the elliptical galaxy NGC 1404. Deep optical images (also
archival) show no sign of this object. From this we conclude that the X-ray
source is the progenitor of the supernova, which favours the accretion model
for this supernova, although the host galaxy is older (6-9 Gyr) than the age at
which the explosions are predicted in the accreting models.Comment: Published in Nature See also the two follow-up papers: Roelofs,
Bassa, Voss, Nelemans Nelemans, Voss, Roelofs, Bassa both on astro-ph
02/15/0
First results of the FP7 SOAP Project
* About the project * Highlights: Gold OA journals today * Results from the large-scale survey of researcher
Open Access Publishing - Models and Attributes
The SOAP (Study of Open Access Publishing) project has compiled data on the present offer for open access publishing in online peer-reviewed journals. Starting from the Directory of Open Access Journals, several sources of data are considered, including inspection of journal web site and direct inquiries within the publishing industry. Several results are derived and discussed, together with their correlations: the number of open access journals and articles; their subject area; the starting date of open access journals; the size and business models of open access publishers; the licensing models; the presence of an impact factor; the uptake of hybrid open access. In addition, a number of qualitative features of open access publishing, relevant to understand the present landscape, are described
WD + MS systems as the progenitor of SNe Ia
We show the initial and final parameter space for SNe Ia in a () plane and find that the positions of some famous
recurrent novae, as well as a supersoft X-ray source (SSS), RX J0513.9-6951,
are well explained by our model. The model can also explain the space velocity
and mass of Tycho G, which is now suggested to be the companion star of Tycho's
supernova. Our study indicates that the SSS, V Sge, might be the potential
progenitor of supernovae like SN 2002ic if the delayed dynamical-instability
model due to Han & Podsiadlowski (2006) is appropriate. Following the work of
Meng, Chen & Han (2009), we found that the SD model (WD + MS) with an optically
thick wind can explain the birth rate of supernovae like SN 2006X and reproduce
the distribution of the color excess of SNe Ia. The model also predicts that at
least 75% of all SNe Ia may show a polarization signal in their spectra.Comment: 6 pages, 2 figures, accepted for publication in Astrophysics & Space
Science (Proceeding of the 4th Meeting on Hot Subdwarf Stars and Related
Objects, edited by Zhanwen Han, Simon Jeffery & Philipp Podsiadlowski
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