1,224 research outputs found
Photometry of SN 2002ic and Implications for the Progenitor Mass-Loss History
We present new pre-maximum and late-time optical photometry of the Type
Ia/IIn supernova 2002ic. These observations are combined with the published
V-band magnitudes of Hamuy et al. (2003) and the VLT spectrophotometry of Wang
et al. (2004) to construct the most extensive light curve to date of this
unusual supernova. The observed flux at late time is significantly higher
relative to the flux at maximum than that of any other observed Type Ia
supernova and continues to fade very slowly a year after explosion. Our
analysis of the light curve suggests that a non-Type Ia supernova component
becomes prominent days after explosion. Modeling of the non-Type Ia
supernova component as heating from the shock interaction of the supernova
ejecta with pre-existing circumstellar material suggests the presence of a
cm gap or trough between the progenitor system and the
surrounding circumstellar material. This gap could be due to significantly
lower mass-loss years prior to explosion or
evacuation of the circumstellar material by a low-density fast wind. The latter
is consistent with observed properties of proto-planetary nebulae and with
models of white-dwarf + asymptotic giant branch star progenitor systems with
the asymptotic giant branch star in the proto-planetary nebula phase.Comment: accepted for publication in Ap
Novae as a Mechanism for Producing Cavities around the Progenitors of SN 2002ic and Other SNe Ia
We propose that a nova shell ejected from a recurrent nova progenitor system
created the evacuated region around the explosion center of SN 2002ic. In this
picture, periodic shell ejections due to nova explosions on a white dwarf sweep
up the slow wind from the binary companion, creating density variations and
instabilities that lead to structure in the circumstellar medium (CSM). Our
model naturally explains the observed gap between the supernova explosion
center and the CSM in SN 2002ic, accounts for the density variations observed
in the CSM, and resolves the coincidence problem of the timing of the explosion
of SN 2002ic with respect to the apparent cessation of mass-loss in the
progenitor system. We also consider such nova outburst sweeping as a generic
feature of Type Ia supernovae with recurrent nova progenitors.Comment: Accepted to ApJL. 11 pages, 1 tabl
Status of the 80Mbit/s Receiver for the CMS digital optical link
The first prototype of the 80Mbit/s optical receiver ASIC for the CMS digital optical link has been manufactured in a 0.25”m commercial CMOS process. The circuit design has been made using radiation tolerant layout techniques. Its performance satisfies the low power, wide dynamic range, sensitivity and speed specifications. The radiation hardness of the receiver has been verified irradiating the diode with 6 MeV neutrons (up to 6.5·1014 n/cm2) and the receiver circuit with 10KeV X-rays (up to 20 Mrad). A second prototype has been submitted for fabrication in the same commercial CMOS process. I
Optical links for the CMS tracker
The development phase of the optical data transfer system for the CMS tracker is nearing completion. This paper focuses on three types of validation tests carried out by CERN on Commercial-Off-The-Shelf electro-optic devices: functionality tests, environmental tests and reliability tests. The project status and the preparation for production are also reviewed. 1
The NN2 Flux Difference Method for Constructing Variable Object Light Curves
We present a new method for optimally extracting point-source time
variability information from a series of images. Differential photometry is
generally best accomplished by subtracting two images separated in time, since
this removes all constant objects in the field. By removing background sources
such as the host galaxies of supernovae, such subtractions make possible the
measurement of the proper flux of point-source objects superimposed on extended
sources. In traditional difference photometry, a single image is designated as
the ``template'' image and subtracted from all other observations. This
procedure does not take all the available information into account and for
sub-optimal template images may produce poor results. Given N total
observations of an object, we show how to obtain an estimate of the vector of
fluxes from the individual images using the antisymmetric matrix of flux
differences formed from the N(N-1)/2 distinct possible subtractions and provide
a prescription for estimating the associated uncertainties. We then demonstrate
how this method improves results over the standard procedure of designating one
image as a ``template'' and differencing against only that image.Comment: Accepted to AJ. To be published in November 2005 issue. 16 page, 2
figures, 2 tables. Source code available at
http://www.ctio.noao.edu/essence/nn2
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Climate Change and San Francisco Bay-Delta Tidal Wetlands
Climate change will affect tidal wetlands with higher rates of sea-level rise and higher concentrations of salt in brackish and freshwater tidal systems, in addition to causing increases in atmospheric CO2 concentration, warmer temperatures, and shifts in precipitation. In the San Francisco BayâDelta, the areas most likely to be affectedâbrackish and freshwater tidal wetlandsâare also the sites with the majority of endemic plant species and the greater biodiversity and productivity. Effects on the San Francisco Bayâ Delta estuary are complex and difficult to predict, but a few things are clear. Biodiversity of the tidal wetland system in the San Francisco BayâDelta region will decline, with subsequent effects on ecosystem functioning and services. Altered plant production, physiological tolerances, and shifts in rates of mortality will modify wetland plant communities in ways not yet predictable. Lower ecosystem productivity from salinity increases will affect both primary and detrital-based food webs. Such changes will cascade via the food webs into invertebrate, bird, and pelagic systems. Tidal wetlands are especially sensitive to processes that climate change will alter. Several of these altered processes are exacerbated by water diversions from the Delta
Model-independent determination of the cosmic expansion rate. I. Application to type-Ia supernovae
Aims: In view of the substantial uncertainties regarding the possible
dynamics of the dark energy, we aim at constraining the expansion rate of the
universe without reference to a specific Friedmann model and its parameters.
Methods: We show that cosmological observables integrating over the cosmic
expansion rate can be converted into a Volterra integral equation which is
known to have a unique solution in terms of a Neumann series. Expanding
observables such as the luminosity distances to type-Ia supernovae into a
series of orthonormal functions, the integral equation can be solved and the
cosmic expansion rate recovered within the limits allowed by the accuracy of
the data. Results: We demonstrate the performance of the method applying it to
synthetic data sets of increasing complexity, and to the first-year SNLS data.
In particular, we show that the method is capable of reproducing a hypothetical
expansion function containing a sudden transition.Comment: 9 pages, 8 figures; accepted by A&A; subsection 3.6 added, new
references and minor change
The Tobacco-Related Behavioral Risks of a Nationally Representative Sample of Adolescents
The study\u27s purpose was to determine which factors were the strongest predictors of tobacco smoking behaviors among U.S. adolescents. The population included a nationally representative sample of 6,504 adolescents residing in the U.S. Data were collected in respondents \u27homes using trained interviewers. Weighted population estimates showed that over half (55.6%) of adolescents had ever tried smoking, nearly half of whom (48.2%) reported regular smoking. Those whose closest friends smoked were twice as likely to ever smoke (OR = 2.24, p\u3c.001), twice as likely to be a regular smoker (OK = 2.28, p \u3c.OO1), and more likely (b = 5.15p \u3c.OO1) to have smoked daily than those whose friends do not smoke. Results show the very strong influence of friendships on tobacco initiation and continuance among this national sample of adolescents. Recommendations for primary and secondary prevention are noted
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