2,413 research outputs found
SN1997cy/GRB970514 - A New Piece in the GRB Puzzle?
We present observations of SN1997cy, a supernova discovered as part of the
Mount Stromlo Abell Cluster SN Search, which does not easily fit into the
traditional classification scheme for supernovae. This object's extraordinary
optical properties and coincidence with GRB970514, a short duration gamma ray
burst, suggest a second case, after SN1998bw/GRB980425, for a SN-GRB
association. SN1997cy is among the most luminous SNe yet discovered and has a
peculiar spectrum. We present evidence that SN1997cy ejected approximately 2
solar masses of 56Ni, supported by its late-time light curve, and FeII/[FeIII]
lines in its spectrum, although it is possible that both these observations can
be explained via circumstellar interaction. While SN1998bw and SN1997cy appear
to be very different objects with respect to both their gamma ray and optical
properties, SN1997cy and the optical transient associated with GRB970508 have
roughly similar late-time optical behavior. This similarity may indicate that
the late-time optical output of these two intrinsically bright transient events
have a common physical process. Although the connection between GRB970514 and
SN1997cy is suggestive, it is not conclusive. However, if this association is
real, followup of short duration GRBs detected with BATSE or HETE2 should
reveal objects similar to SN1997cy.Comment: 26 pages including 6 postscript figures and 3 tables. Submitted to
ApJ. Re-calibrated photometry - objects are about 0.3mags brighter than in
original versio
The Detection of a Cooling Flow Elliptical Galaxy from OVI Emission
Cooling flow models for the hot gas in elliptical galaxies predict that gas
is cooling at a rate of ~ 1 solar mass/yr, yet there is little evidence for
this phenomenon beyond the X-ray waveband. If hot gas is cooling, it will pass
through the 3x10^5 K regime and radiate in the OVI 1032,1038 ultraviolet lines,
which can be detected with the Far Ultraviolet Spectroscopic Explorer (FUSE)
and here we report on FUSE observations of the X-ray bright early-type galaxies
NGC 1404 and NGC 4636. In NGC 1404, the OVI doublet is not detected, implying a
cooling rate < 0.3 solar masses/yr, which is below the predicted values from
the cooling flow model of 0.4-0.9 solar masses/yr. In NGC 4636, both OVI lines
are clearly detected, indicating a cooling rate of 0.43 +/- 0.06 solar
masses/yr, which falls within the range of values from the cooling flow
prediction, 0.36-2.3 solar masses/yr and is closest to the model where the
production of the cooled gas is distributed through the galaxy. The emission
line widths, 44 +/- 15 km/s, are close to the Doppler broadening value (30
km/s), indicating that the flow is quiescent rather than turbulent, and that
the flow velocity is < 30 km/s.Comment: to be published in ApJ Letters; 8 Latex pages with 2 embedded figure
Effects of combined conservation practices on soil and water quality in the Central Mississippi River Basin
Conventional cultivation of claypan soils leads to soil and water quality degradation because of high runoff and associated soil erosion. The Goodwater Creek Experimental Watershed, which is part of the USDA Agricultural Research Service Benchmark Conservation Effects Assessment Project, Watershed Assessment Studies, was established to address these issues. Plot studies have highlighted trade-offs between erosion control and herbicide or nutrient runoff. There is a need for long-term field-scale evaluation of combined practices that reduce sediment, nutrient, and herbicide losses by runoff. A 36 ha field located in Missouri was under a conventional corn (Zea mays L.)-soybean (Glycine max L.) system from 1993 to 2003 with fertilizer application and tillage prior to planting in the spring. A precision agriculture system defined by two main management zones was implemented from 2004 to 2014: Wheat (Triticum aestivum L.) and soybean in 60% of the field, and corn and soybean in the remaining 40%. The system included no-till, cover crops, atrazine split-applications based on weed pressure, variable rates of nitrogen (N), and variable rates of fall-applied phosphorus (P). The objective of this study was to compare runoff water quality from the two management systems, based on flow and load duration curves, cumulative distribution functions, and conclusions from replicated plot studies. The precision agriculture system did not affect annual runoff, but it did increase the frequency of low flows. Sediment losses were reduced by 87% as a result of no-till and cover crops. Atrazine and P losses were lower than expected, despite the lack of incorporation into the soil. Atrazine losses were possibly lower because of the wheat area acting as a buffer, greater atrazine adsorption and retention in the field, and faster decay. Dissolved P losses as a fraction of applied remained the same, likely because of greater adsorption and lower runoff risk when applying P. Finally, nitrate-N (NO3-N) losses decreased and resulted in an overall decrease of N losses despite a slight increase of ammonium-N (NH4-N) losses. Explanations includeincluded a greater soil water content, a different timing of N applications, and N uptake by cover crops. Building on these successes, an aspirational management system is proposed to further improve on the performance and practicality of the precision agriculture system
The CoNFIG Catalogue - II. Comparison of Space Densities in the FR Dichotomy
This paper focuses on a comparison of the space densities of FRI and FRII
sources at different epochs, with a particular focus on FRI sources. First, we
present the concluding steps in constructing the Combined NVSS-FIRST Galaxy
catalogue (CoNFIG), including new VLA observations, optical identifications and
redshift estimates. The final catalogue consists of 859 sources over 4 samples
(CoNFIG-1, 2, 3 and 4 with flux density limits of S_1.4GHz = 1.3, 0.8, 0.2 and
0.05 Jy respectively). It is 95.7% complete in radio morphology classification
and 74.3% of the sources have redshift data. Combining CoNFIG with
complementary samples, the distribution and evolution of FRI and FRII sources
are investigated. We find that FRI sources undergo mild evolution and that, at
the same radio luminosity, FRI and FRII sources show similar space density
enhancements in various redshift ranges, possibly implying a common evolution.Comment: 15 pages, 15 figures, 6 tables + appendix (80 pages). accepted in
M.N.R.A.
Extended Emission Line Gas in Radio Galaxies - PKS0349-27
PKS0349-27 is a classical FRII radio galaxy with an AGN host which has a
spectacular, spiral-like structure in its extended emission line gas (EELG). We
have measured the velocity field in this gas and find that it splits into 2
cloud groups separated by radial velocities which at some points approach 400
km/s Measurements of the diagnostic emission line ratios [OIII]5007/H-beta,
[SII]6716+6731/H-alpha, and [NII]6583/H-alpha in these clouds show no evidence
for the type of HII region emission associated with starburst activity in
either velocity system. The measured emission line ratios are similar to those
found in the nuclei of narrow-line radio galaxies, but the extended
ionization/excitation cannot be produced by continuum emission from the active
nucleus alone. We present arguments which suggest that the velocity
disturbances seen in the EELG are most likely the result of a galaxy-galaxy
collision or merger but cannot completely rule out the possibility that the gas
has been disrupted by the passage of a radio jet.Comment: 12 pages, 3 fig pages, to appear in the Astrophys.
Pictor A (PKS 0518-45) - From Nucleus to Lobes
We present radio and optical imaging and kinematic data for the radio galaxy
Pictor A, including HST continuum and [OIII], emission-line images (at a
resolution of 25 - 100 mas) and ground-based imaging and spectroscopy (at a
resolution of ~ 1.5". The radio data include 3 cm Australia Telescope images of
the core, at a resolution comparable to that of the optical, ground-based
images, and a VLBI image of a jet in the compact core (at a resolution of 2 -
25 mas), which seems to align with a continuum ``jet'' found in the HST images.
The core radio jet, the HST optical continuum ``jet'', and the NW H-alpha
filaments all appear to point toward the optical-synchrotron hot-spot in the NW
lobe of this object and are associated with a disrupted velocity field in the
extended ionized gas. The ground-based spectra which cover this trajectory also
yield line ratios for the ionized gas which have anomalously low [NII] (6564),
suggesting either a complex, clumpy structure in the gas with a higher
cloud-covering factor at larger radii and with denser clouds than is found in
the nuclear regions of most NLRG and Seyfert 2 galaxies, or some other,
unmodeled, mechanism for the emergent spectrum from this region. The H-alpha
emission-line filaments to the N appear to be associated with a 3 cm radio
continuum knot which lies in a gap in the filaments ~ 4" from the nucleus.
Altogether, the data in this paper provide good circumstantial evidence for
non-disruptive redirection of a radio jet by interstellar gas clouds in the
host galaxy.Comment: 19 pages, 6 ps.gz fig pages, to appear in the Ap.J. Supp
Expression of von Willebrand factor "Normandy": an autosomal mutation that mimics hemophilia A.
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