Beam Profile Measurements and Simulations of the PETRA Laser-Wire

The Laser-wire will be an essential diagnostic tool at the International Linear Collider. It uses a finely focussed laser beam to measure the transverse profile of electron bunches by detecting the Compton-scattered photons (or degraded electrons) downstream of where the laser beam intersects the electron beam. Such a system has been installed at the PETRA storage ring at DESY, which uses a piezo-driven mirror to scan the laser-light across the electron beam. Lat- est results of experimental data taking are presented and compared to detailed simulations using the Geant4 based program BDSIM.Comment: 3 pagesm 4 figures. Submitted as a conference paper for the Particle Accelerator Conference 2005 (PAC05

Photometric selection of Type Ia supernovae in the Supernova Legacy Survey

We present a sample of 485 photometrically identified Type Ia supernova candidates mined from the first three years of data of the CFHT SuperNova Legacy Survey (SNLS). The images were submitted to a deferred processing independent of the SNLS real-time detection pipeline. Light curves of all transient events were reconstructed in the g_M, r_M, i_M and z_M filters and submitted to automated sequential cuts in order to identify possible supernovae. Pure noise and long-term variable events were rejected by light curve shape criteria. Type Ia supernova identification relied on event characteristics fitted to their light curves assuming the events to be normal SNe Ia. The light curve fitter SALT2 was used for this purpose, assigning host galaxy photometric redshifts to the tested events. The selected sample of 485 candidates is one magnitude deeper than that allowed by the SNLS spectroscopic identification. The contamination by supernovae of other types is estimated to be 4%. Testing Hubble diagram residuals with this enlarged sample allows us to measure the Malmquist bias due to spectroscopic selections directly. The result is fully consistent with the precise Monte Carlo based estimate used to correct SN Ia distance moduli in the SNLS 3-year cosmological analyses. This paper demonstrates the feasibility of a photometric selection of high redshift supernovae with known host galaxy redshifts, opening interesting prospects for cosmological analyses from future large photometric SN Ia surveys.Comment: (The SNLS collaboration) 23 pages, 28 figures, Accepted in A&

Gemini Spectroscopy of Supernovae from SNLS: Improving High Redshift SN Selection and Classification

We present new techiques for improving the efficiency of supernova (SN) classification at high redshift using 64 candidates observed at Gemini North and South during the first year of the Supernova Legacy Survey (SNLS). The SNLS is an ongoing five year project with the goal of measuring the equation of state of Dark Energy by discovering and following over 700 high-redshift SNe Ia using data from the Canada-France-Hawaii Telescope Legacy Survey. We achieve an improvement in the SN Ia spectroscopic confirmation rate: at Gemini 71% of candidates are now confirmed as SNe Ia, compared to 54% using the methods of previous surveys. This is despite the comparatively high redshift of this sample, where the median SN Ia redshift is z=0.81 (0.155 <= z <= 1.01). These improvements were realized because we use the unprecedented color coverage and lightcurve sampling of the SNLS to predict whether a candidate is an SN Ia and estimate its redshift, before obtaining a spectrum, using a new technique called the "SN photo-z." In addition, we have improved techniques for galaxy subtraction and SN template chi^2 fitting, allowing us to identify candidates even when they are only 15% as bright as the host galaxy. The largest impediment to SN identification is found to be host galaxy contamination of the spectrum -- when the SN was at least as bright as the underlying host galaxy the target was identified more than 90% of the time. However, even SNe on bright host galaxies can be easily identified in good seeing conditions. When the image quality was better than 0.55 arcsec the candidate was identified 88% of the time. Over the five-year course of the survey, using the selection techniques presented here we will be able to add approximately 170 more confirmed SNe Ia than would be possible using previous methods.Comment: ApJ, accepted, 19 pages, 9 figure

The effect of progenitor age and metallicity on luminosity and 56Ni yield in Type Ia supernovae

Timmes, Brown & Truran found that metallicity variations could theoretically account for a 25% variation in the mass of 56Ni synthesized in Type Ia supernovae (SNe Ia), and thus account for a large fraction of the scatter in observed SN Ia luminosities. Higher-metallicity progenitors are more neutron-rich, producing more stable burning products relative to radioactive 56Ni. We develop a new method for estimating bolometric luminosity and 56Ni yield in SNe Ia and use it to test the theory with data from the Supernova Legacy Survey. We find that the average 56Ni yield does drop in SNe Ia from high metallicity environments, but the theory can only account for 7%--10% of the dispersion in SN Ia 56Ni mass, and thus luminosity. This is because the effect is dominant at metallicities significantly above solar, whereas we find that SN hosts have predominantly subsolar or only moderately above-solar metallicities. We also show that allowing for changes in O/Fe with the metallicity [Fe/H] does not have a major effect on the theoretical prediction of Timmes, Brown & Truran, so long as one is using the O/H as the independent variable. Age may have a greater effect than metallicity -- we find that the luminosity weighted age of the host galaxy is correlated with 56Ni yield, and thus more massive progenitors give rise to more luminous explosions. This is hard to understand if most SNe Ia explode when the primaries reach the Chandrasekhar mass. Finally, we test the findings of Gallagher et al., that the residuals of SNe Ia from the Hubble diagram are correlated with host galaxy metallicity, and we find no such correlation.Comment: ApJ, accepted, 34 pages, 11 figures, apologies for one column format -- necessary for the equation

Gravitational red-shift and deflection of slow light

We explore the nature of the classical propagation of light through media with strong frequency-dependent dispersion in the presence of a gravitational field. In the weak field limit, gravity causes a redshift of the optical frequency, which the slow-light medium converts into a spatially-varying index of refraction. This results in the bending of a light ray in the medium. We further propose experimental techniques to amplify and detect the phenomenon using weak value measurements. Independent heuristic and rigorous derivations of this effect are given.Comment: 9 pages, 1 figur

EPIC 219217635: A Doubly Eclipsing Quadruple System Containing an Evolved Binary

We have discovered a doubly eclipsing, bound, quadruple star system in the field of K2 Campaign 7. EPIC 219217635 is a stellar image with $Kp = 12.7$ that contains an eclipsing binary (`EB') with $P_A = 3.59470$ d and a second EB with $P_B = 0.61825$ d. We have obtained followup radial-velocity (`RV') spectroscopy observations, adaptive optics imaging, as well as ground-based photometric observations. From our analysis of all the observations, we derive good estimates for a number of the system parameters. We conclude that (1) both binaries are bound in a quadruple star system; (2) a linear trend to the RV curve of binary A is found over a 2-year interval, corresponding to an acceleration, $\dot \gamma = 0.0024 \pm 0.0007$ cm s$^{-2}$; (3) small irregular variations are seen in the eclipse-timing variations (`ETVs') detected over the same interval; (4) the orbital separation of the quadruple system is probably in the range of 8-25 AU; and (5) the orbital planes of the two binaries must be inclined with respect to each other by at least 25$^\circ$. In addition, we find that binary B is evolved, and the cooler and currently less massive star has transferred much of its envelope to the currently more massive star. We have also demonstrated that the system is sufficiently bright that the eclipses can be followed using small ground-based telescopes, and that this system may be profitably studied over the next decade when the outer orbit of the quadruple is expected to manifest itself in the ETV and/or RV curves.Comment: Accepted for publication in MNRA

Combining airborne gas and aerosol measurements with HYSPLIT: a visualization tool for simultaneous evaluation of air mass history and back trajectory consistency

The history of air masses is often investigated using backward trajectories to gain knowledge about processes along the air parcel path as well as possible source regions. Here, we describe a refined approach that incorporates airborne gas, aerosol, and environmental data into back trajectories and show how this technique allows for simultaneous evaluation of air mass history and back trajectory reliability without the need to calculate trajectory errors. <br><br> We use the HYbrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) model and add a simple semi-automated computing routine to facilitate high-frequency coverage of back trajectories initiated along free tropospheric (FT) flight tracks and profiles every 10 s. We integrate our in situ physiochemical data by color-coding each of these trajectories with its corresponding in situ tracer values measured at the back trajectory start points along the flight path. The unique color for each trajectory aids assessment of trajectory reliability through the visual clustering of air mass pathways of similar coloration. Moreover, marked changes in trajectories associated with marked changes evident in measured physiochemical or thermodynamic properties of an air mass add credence to trajectories. This is particularly true when these air mass properties are linked to trajectory features characteristic of recognized sources or processes. This visual clustering of air mass pathways is of particular value for large-scale 3-D flight tracks common to aircraft experiments where air mass features of interest are often spatially distributed and temporally separated. <br><br> The cluster-visualization tool used here reveals that most FT back trajectories with pollution signatures measured in the central equatorial Pacific reach back to sources on the South American continent over 10 000 km away and 12 days back in time, e.g., the Amazonian basin. We also demonstrate the distinctions in air mass properties between these and trajectories that penetrate deep convection in the Inter-Tropical Convergence Zone. Additionally, for the first time we show consistency of modeled precipitation along back trajectories with scavenging signatures in the aerosol measured for these trajectories

The Type Ia Supernova Rate in Radio and Infrared Galaxies from the CFHT Supernova Legacy Survey

We have combined the large SN Ia database of the Canada-France-Hawaii Telescope Supernova Legacy Survey and catalogs of galaxies with photometric redshifts, VLA 1.4 GHz radio sources, and Spitzer infrared sources. We present eight SNe Ia in early-type host galaxies which have counterparts in the radio and infrared source catalogs. We find the SN Ia rate in subsets of radio and infrared early-type galaxies is ~1-5 times the rate in all early-type galaxies, and that any enhancement is always <~ 2 sigma. Rates in these subsets are consistent with predictions of the two component "A+B" SN Ia rate model. Since infrared properties of radio SN Ia hosts indicate dust obscured star formation, we incorporate infrared star formation rates into the "A+B" model. We also show the properties of SNe Ia in radio and infrared galaxies suggest the hosts contain dust and support a continuum of delay time distributions for SNe Ia, although other delay time distributions cannot be ruled out based on our data.Comment: 14 pages, 6 figures, 7 tables, accepted for publication in A

Footprints in Sand: The Response of a Granular Material to Local Perturbations

We experimentally determine ensemble-averaged responses of granular packings to point forces, and we compare these results to recent models for force propagation in a granular material. We used 2D granular arrays consisting of photoelastic particles: either disks or pentagons, thus spanning the range from ordered to disordered packings. A key finding is that spatial ordering of the particles is a key factor in the force response. Ordered packings have a propagative component that does not occur in disordered packings.Comment: 5 pages, 4 eps figures, Phys. Rev. Lett. 87, 035506 (2001