Determination of the Neutron Beta-Decay Asymmetry Parameter \u3cem\u3eA\u3c/em\u3e Using Polarized Ultracold Neutrons

The UCNA Experiment at the Los Alamos Neutron Science Center (LANSCE) is the first measurement of the β-decay asymmetry parameter A0 using polarized ultracold neutrons (UCN). A0 , which represents the parity-violating angular correlation between the direction of the initial neutron spin and the emitted decay electron’s momentum, determines λ = gA /gV , the ratio of the weak axial-vector and vector coupling constants. A high-precision determination of λ is important for weak interaction physics, and when combined with the neutron lifetime it permits an extraction of the CKM matrix element Vud solely from neutron decay. At LANSCE, UCN are produced in a pulsed, spallation driven solid deuterium source and then polarized via transport through a 7 T magnetic field. Their spins can then be flipped via transport through an Adiabatic Fast Passage spin flipper located in a low-field-gradient 1 T field region prior to transport to a decay storage volume situated within a 1 T solenoidal spectrometer. Electron detector packages located at each end of the spectrometer provide for the measurement of decay electrons. Previous UCNA results (based on data collected in 2010 and earlier) were limited by systematic uncertainties, in particular those from the UCN polarization, calibration of the electron energy, electron backscattering, and angular acceptance of events. This dissertation will present a background of neutron decay, an overview of the UCNA Experiment, followed by a detailed report on the entire analysis process for data acquired during run periods in 2011-2012 and 2012-2013

An 11.6 Micron Keck Search For Exozodiacal Dust

We have begun an observational program to search nearby stars for dust disks that are analogous to the disk of zodiacal dust that fills the interior of our solar system. We imaged six nearby main-sequence stars with the Keck telescope at 11.6 microns, correcting for atmosphere-induced wavefront aberrations and deconvolving the point spread function via classical speckle analysis. We compare our data to a simple model of the zodiacal dust in our own system based on COBE/DIRBE observations and place upper limits on the density of exozodiacal dust in these systems.Comment: 10 pages, figure1, figure2, figure3, and figures 4a-

Travel time stability in weakly range-dependent sound channels

Travel time stability is investigated in environments consisting of a range-independent background sound-speed profile on which a highly structured range-dependent perturbation is superimposed. The stability of both unconstrained and constrained (eigenray) travel times are considered. Both general theoretical arguments and analytical estimates of time spreads suggest that travel time stability is largely controlled by a property $\omega ^{\prime}$ of the background sound speed profile. Here, $2\pi/\omega (I)$ is the range of a ray double loop and $I$ is the ray action variable. Numerical results for both volume scattering by internal waves in deep ocean environments and rough surface scattering in upward refracting environments are shown to confirm the expectation that travel time stability is largely controlled by $\omega ^{\prime}$.Comment: Submitted to J. Acoust. Soc. Am., 30 June 200

Planetary astronomy

The authors profile the field of astronomy, identify some of the key scientific questions that can be addressed during the decade of the 1990's, and recommend several facilities that are critically important for answering these questions. Scientific opportunities for the 1990' are discussed. Areas discussed include protoplanetary disks, an inventory of the solar system, primitive material in the solar system, the dynamics of planetary atmospheres, planetary rings and ring dynamics, the composition and structure of the atmospheres of giant planets, the volcanoes of IO, and the mineralogy of the Martian surface. Critical technology developments, proposed projects and facilities, and recommendations for research and facilities are discussed

A photometrically and spectroscopically confirmed population of passive spiral galaxies

We have identified a population of passive spiral galaxies from photometry and integral field spectroscopy. We selected z < 0.035 spiral galaxies that have WISE colours consistent with little mid-infrared emission from warm dust. Matched aperture photometry of 51 spiral galaxies in ultraviolet, optical and mid-infrared show these galaxies have colours consistent with passive galaxies. Six galaxies form a spectroscopic pilot study and were observed using the Wide-Field Spectrograph to check for signs of nebular emission from star formation. We see no evidence of substantial nebular emission found in previous red spiral samples. These six galaxies possess absorption-line spectra with 4000 Å breaks consistent with an average luminosity-weighted age of 2.3 Gyr. Our photometric and integral field spectroscopic observations confirm the existence of a population of local passive spiral galaxies, implying that transformation into early-type morphologies is not required for the quenching of star formation

RR Lyrae Stars in the Andromeda Halo from Deep Imaging with the Advanced Camera for Surveys

We present a complete census of RR Lyrae stars in a halo field of the Andromeda galaxy. These deep observations, taken as part of a program to measure the star formation history in the halo, spanned a period of 41 days with sampling on a variety of time scales, enabling the identification of short and long period variables. Although the long period variables cannot be fully characterized within the time span of this program, the enormous advance in sensitivity provided by the Advanced Camera for Surveys on the Hubble Space Telescope allows accurate characterization of the RR Lyrae population in this field. We find 29 RRab stars with a mean period of 0.594 days, 25 RRc stars with a mean period of 0.316 days, and 1 RRd star with a fundamental period of 0.473 days and a first overtone period of 0.353 days. These 55 RR Lyrae stars imply a specific frequency S_RR=5.6, which is large given the high mean metallicity of the halo, but not surprising given that these stars arise from the old, metal-poor tail of the distribution. This old population in the Andromeda halo cannot be clearly placed into one of the Oosterhoff types: the ratio of RRc/RRabc stars is within the range seen in Oosterhoff II globular clusters, the mean RRab period is in the gap between Oosterhoff types, and the mean RRc period is in the range seen in Oosterhoff I globular clusters. The periods of these RR Lyraes suggest a mean metallicity of [Fe/H]=-1.6, while their brightness implies a distance modulus to Andromeda of 24.5+/-0.1, in good agreement with the Cepheid distance.Comment: 15 pages, latex. Accepted for publication in The Astronomical Journa

High-accuracy comparison of numerical relativity simulations with post-Newtonian expansions

Numerical simulations of 15 orbits of an equal-mass binary black hole system are presented. Gravitational waveforms from these simulations, covering more than 30 cycles and ending about 1.5 cycles before merger, are compared with those from quasi-circular zero-spin post-Newtonian (PN) formulae. The cumulative phase uncertainty of these comparisons is about 0.05 radians, dominated by effects arising from the small residual spins of the black holes and the small residual orbital eccentricity in the simulations. Matching numerical results to PN waveforms early in the run yields excellent agreement (within 0.05 radians) over the first $\sim 15$ cycles, thus validating the numerical simulation and establishing a regime where PN theory is accurate. In the last 15 cycles to merger, however, {\em generic} time-domain Taylor approximants build up phase differences of several radians. But, apparently by coincidence, one specific post-Newtonian approximant, TaylorT4 at 3.5PN order, agrees much better with the numerical simulations, with accumulated phase differences of less than 0.05 radians over the 30-cycle waveform. Gravitational-wave amplitude comparisons are also done between numerical simulations and post-Newtonian, and the agreement depends on the post-Newtonian order of the amplitude expansion: the amplitude difference is about 6--7% for zeroth order and becomes smaller for increasing order. A newly derived 3.0PN amplitude correction improves agreement significantly ($<1$ amplitude difference throughout most of the run, increasing to 4% near merger) over the previously known 2.5PN amplitude terms.Comment: Updated to agree with published version (various minor clarifications; added description of AH finder in Sec IIB; added discussion of tidal heating in Sec VC

Near-ultraviolet signatures of environment-driven galaxy quenching in Sloan Digital Sky Survey groups

© 2016 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. We have investigated the effect of group environment on residual star formation in galaxies, using Galaxy Evolution Explorer near-ultraviolet (NUV) galaxy photometry with the Sloan Digital Sky Survey group catalogue of Yang et al. We compared the (NUV - r) colours of grouped and non-grouped galaxies, and find a significant increase in the fraction of red sequence galaxies with blue (NUV - r) colours outside of groups. When comparing galaxies in mass-matched samples of satellite (non-central), and non-grouped galaxies, we found a > 4σ difference in the distribution of (NUV - r) colours, and an (NUV - r) blue fraction > 3σ higher outside groups. A comparison of satellite and non-grouped samples has found the NUV fraction is a factor of ~2 lower for satellite galaxies between 10 10.5 and 10 10.7 M ⊙ , showing that higher mass galaxies are more likely to have residual star formation when not influenced by a group potential. There was a higher (NUV - r) blue fraction of galaxies with lower Sérsic indices (n < 3) outside of groups, not seen in the satellite sample. We have used stellar population models of Bruzual & Charlot with multiple burst, or exponentially declining star formation histories to find that many of the (NUV - r) blue non-grouped galaxies can be explained by a slow (~2 Gyr) decay of star formation, compared to the satellite galaxies. We suggest that taken together, the difference in (NUV - r) colours between samples can be explained by a population of secularly evolving, non-grouped galaxies, where star formation declines slowly. This slow channel is less prevalent in group environments where more rapid quenching can occur