Spectral Consequences of Deviation from Spherical Composition Symmetry in Type Ia Supernovae

We investigate the prospects for constraining the maximum scale of clumping in composition that is consistent with observed Type Ia supernova flux spectra. Synthetic spectra generated without purely spherical composition symmetry indicate that gross asymmetries make prominent changes to absorption features. Motivated by this, we consider the case of a single unblended line forming in an atmosphere with perturbations of different scales and spatial distributions. Perturbations of about 1% of the area of the photodisk simply weaken the absorption feature by the same amount independent of the line of sight. Conversely, perturbations of about 10% of the area of the photodisk introduce variation in the absorption depth which does depend on the line of sight. Thus, 1% photodisk area perturbations may be consistent with observed profile homogeneity but 10% photodisk area perturbations can not. Based on this, we suggest that the absence of significant variation in the depths of Si II 6355 absorption features in normal Type Ia spectra near maximum light indicates that any composition perturbations in these events are quite small. This also constrains future three-dimensional explosion models to produce ejecta profiles with only small scale inhomogeneities.Comment: 11 pages, 6 figure

High frequency dynamics in a monatomic glass

The high frequency dynamics of glassy Selenium has been studied by Inelastic X-ray Scattering at beamline BL35XU (SPring-8). The high quality of the data allows one to pinpoint the existence of a dispersing acoustic mode for wavevectors ($Q$) of $1.5<Q<12.5$ nm$^{-1}$, helping to clarify a previous contradiction between experimental and numerical results. The sound velocity shows a positive dispersion, exceeding the hydrodynamic value by $\approx$ 10% at $Q<3.5$ nm$^{-1}$. The $Q^2$ dependence of the sound attenuation $\Gamma(Q)$, reported for other glasses, is found to be the low-$Q$ limit of a more general $\Gamma(Q) \propto \Omega(Q)^2$ law which applies also to the higher $Q$ region, where $\Omega(Q)\propto Q$ no longer holds.Comment: Phys. Rev. Lett. (Accepted

On the High--Velocity Ejecta of the Type Ia Supernova 1994D

Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared to spectra of the Type Ia SN 1994D that were obtained before the time of maximum brightness. Evidence is found for the presence of two-component Fe II and Ca II features, forming in high velocity ($\ge 20,000$ \kms) and lower velocity ($\le 16,000$ \kms) matter. Possible interpretations of these spectral splits, and implications for using early--time spectra of SNe Ia to probe the metallicity of the progenitor white dwarf and the nature of the nuclear burning front in the outer layers of the explosion, are discussed.Comment: 15 pages, 3 figures, 3 tables, Astrophysical Journal, in pres

Implementing the GBT Data Transmission Protocol in FPGAs

International audienceThe GBT chip is a radiation tolerant ASIC that can be used to implement bidirectional multipurpose 4.8 Gb/s optical links for high-energy physics experiments. It will be proposed to the LHC experiments for combined transmission of physics data, trigger, timing, fast and slow control and monitoring. Although radiation hardness is required on detectors, it is not necessary for the electronics located in the counting rooms. Therefore, a study is being made to implement these GBT links on FPGAs. This paper will describe the GBT protocol implementation, the configuration of the transceivers on Altera Stratix II GX and Xilinx Virtex 4, the optimization of resource for multi-transceivers, the first data transmission tests and the source code availabilit

Brief Report: The Go/No-Go Task Online: Inhibitory Control Deficits in Autism in a Large Sample.

Autism Spectrum Conditions (ASC, also referred to as Autism Spectrum Disorders) entail difficulties with inhibition: inhibiting action, inhibiting one's own point of view, and inhibiting distractions that may interfere with a response set. However, the association between inhibitory control (IC) and ASC, especially in adulthood, is unclear. The current study measured IC, using the Go/No-Go task online, in a large adult sample of 201 people with ASC and 240 controls. Number of both False Alarm and False Positive responses were significantly associated with autistic traits and diagnostic status, separately, but not jointly. These findings suggest that deficits in inhibition are associated with ASC. Future studies need to investigate the role of inhibition in ASC in everyday difficulties.This research was supported by the Autism Research Trust, the Medical Research Council (MRC) and EU-AIMS. FU was supported by the British Friends of Haifa University, the Israel Science Foundation (Grant No. 449/14), the British Friends of Hebrew University, and the Joseph Levy Charitable Foundatio

Spectral Modeling of SNe Ia Near Maximum Light: Probing the Characteristics of Hydro Models

We have performed detailed NLTE spectral synthesis modeling of 2 types of 1-D hydro models: the very highly parameterized deflagration model W7, and two delayed detonation models. We find that overall both models do about equally well at fitting well observed SNe Ia near to maximum light. However, the Si II 6150 feature of W7 is systematically too fast, whereas for the delayed detonation models it is also somewhat too fast, but significantly better than that of W7. We find that a parameterized mixed model does the best job of reproducing the Si II 6150 line near maximum light and we study the differences in the models that lead to better fits to normal SNe Ia. We discuss what is required of a hydro model to fit the spectra of observed SNe Ia near maximum light.Comment: 29 pages, 14 figures, ApJ, in pres

Type Ia Supernova Spectral Line Ratios as Luminosity Indicators

Type Ia supernovae have played a crucial role in the discovery of the dark energy, via the measurement of their light curves and the determination of the peak brightness via fitting templates to the observed lightcurve shape. Two spectroscopic indicators are also known to be well correlated with peak luminosity. Since the spectroscopic luminosity indicators are obtained directly from observed spectra, they will have different systematic errors than do measurements using photometry. Additionally, these spectroscopic indicators may be useful for studies of effects of evolution or age of the SNe Ia progenitor population. We present several new variants of such spectroscopic indicators which are easy to automate and which minimize the effects of noise. We show that these spectroscopic indicators can be measured by proposed JDEM missions such as SNAP and JEDI.Comment: 50 pages, 19 figures, 24 tables, submitted to Ap