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Turner, D

Publications and source records attributed to Turner, D.

8 records
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

Plains Elevated Convection at Night (PECAN) Experiment Science Plan

The Plains Elevated Convection at Night (PECAN) experiment is a large field campaign that is being supported by the National Science Foundation (NSF) with contributions from the National Oceanic and Atmospheric Administration (NOAA), the National Atmospheric and Space Administration (NASA), and the U.S. Department of Energy (DOE). The overarching goal of the PECAN experiment is to improve the understanding and simulation of the processes that initiate and maintain convection and convective precipitation at night over the central portion of the Great Plains region of the United States (Parsons et al. 2013). These goals are important because (1) a large fraction of the yearly precipitation in the Great Plains comes from nocturnal convection, (2) nocturnal convection in the Great Plains is most often decoupled from the ground and, thus, is forced by other phenomena aloft (e.g., propagating bores, frontal boundaries, low-level jets [LLJ], etc.), (3) there is a relative lack of understanding how these disturbances initiate and maintain nocturnal convection, and (4) this lack of understanding greatly hampers the ability of numerical weather and climate models to simulate nocturnal convection well. This leads to significant uncertainties in predicting the onset, location, frequency, and intensity of convective cloud systems and associated weather hazards over the Great Plains.

Turner, D↗
DOE OSTI2012

THE IMPACT OF CONTAMINATED RR LYRAE/GLOBULAR CLUSTER PHOTOMETRY ON THE DISTANCE SCALE

RR Lyrae variables and the stellar constituents of globular clusters are employed to establish the cosmic distance scale and age of the universe. However, photometry for RR Lyrae variables in the globular clusters M3, M15, M54, M92, NGC 2419, and NGC 6441 exhibit a dependence on the clustercentric distance. For example, variables and stars positioned near the crowded high-surface brightness cores of the clusters may suffer from photometric contamination, which invariably affects a suite of inferred parameters (e.g., distance, color excess, absolute magnitude, etc.). The impetus for this study is to mitigate the propagation of systematic uncertainties by increasing awareness of the pernicious impact of contaminated and radial-dependent photometry.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DISCOVERY OF THE HOST CLUSTER FOR THE FUNDAMENTAL CEPHEID CALIBRATOR ZETA GEMINORUM

New and existing CORAVEL, UBVJHK{sub s} , HST, HIP/Tycho, ARO, KPNO, and DAO observations imply that the fundamental Cepheid calibrator {zeta} Gem is a cluster member. The following parameters were inferred for {zeta} Gem from cluster membership and are tied to new spectral classifications (DAO) established for 26 nearby stars (e.g., HD53588/B7.5IV, HD54692/B9.5IV): E{sub B-V} = 0.02 {+-} 0.02, log {tau} = 7.85 {+-} 0.15, and d = 355 {+-} 15 pc. The mean distance to {zeta} Gem from cluster membership and six recent estimates (e.g., IRSB) is d=363{+-}9({sigma}{sub x}-bar ){+-}26 ({sigma}) pc. The results presented here support the color-excess and HST parallax derived for the Cepheid by Benedict et al. Forthcoming precise proper motions (DASCH) and Chandra/XMM-Newton observations of the broader field may be employed to identify cluster members, bolster the cluster's existence, and provide stronger constraints on the Cepheid's fundamental parameters.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

NEW EVIDENCE SUPPORTING CLUSTER MEMBERSHIP FOR THE KEYSTONE CALIBRATOR DELTA CEPHEI

New and existing UBVJHK{sub s} , spectroscopic, NOMAD, Hubble Space Telescope, and revised Hipparcos observations are employed to determine properties for {delta} Cep and its host star cluster. The multi-faceted approach ensured that uncertainties were mitigated ({sigma}/d {approx} 2%). The following fundamental parameters were inferred for {delta} Cep: E(B - V) = 0.073 {+-} 0.018({sigma}), log {tau} = 7.9 {+-} 0.1, and d=272 {+-} 3({sigma}{sub x}-bar) {+-} 5 ({sigma}) pc. The cluster exhibits a turnoff near B6 (M{sub *}/M{sub Sun} {approx} 5), and the brightest host cluster members are the supergiants {zeta} Cep (K1.5Ib) and {delta} Cep. To within the uncertainties, the two stars share common astrometric parameters ({pi}, {mu}{sub {alpha}}, {mu}{sub {delta}}, RV {approx} -17 km s{sup -1}) and are tied to bluer members via the evolutionary track implied by the cluster's UBVJHK{sub s} color-color and color-magnitude diagrams. The cluster's existence is bolstered by the absence of an early-type sequence in color-magnitude diagrams for comparison fields. NOMAD data provided a means to identify potential cluster members (n {approx} 30) and double the existing sample. That number could increase with forthcoming precise proper motions (DASCH) for fainter main-sequence stars associated with classical Cepheids (e.g., {delta} Cep), which may invariably foster efforts to strengthen the Galactic Cepheid calibration and reduce uncertainties tied to H{sub 0}.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

Hidden Superlattice in Tl2(SC6H4S) and Tl2(SeC6H4Se) Solved from Powder X-ray Diffraction

The crystal structures of the isostructural title compounds poly[({mu}-benzene-1,4-dithiolato)dithallium], Tl{sub 2}(SC{sub 6}H{sub 4}S), and poly[({mu}-benzene-1,4-diselenolato)dithallium], Tl{sub 2}(SeC{sub 6}H{sub 4}Se), were solved by simulated annealing from high-resolution synchrotron X-ray powder diffraction. Rietveld refinements of an initial structure with one formula unit per triclinic cell gave satisfactory agreement with the data, but led to a structure with impossibly close non-bonded contacts. A disordered model was proposed to alleviate this problem, but an alternative supercell structure leads to slightly improved agreement with the data. The isostructural superlattice structures were confirmed for both compounds through additional data collection, with substantially better counting statistics, which revealed the presence of very weak superlattice peaks not previously seen. Overall, each structure contains Tl-S or Tl-Se two-dimensional networks, connected by phenylene bridges. The sulfur (or selenium) coordination sphere around each thallium is a highly distorted square pyramid or a 'see-saw' shape, depending upon how many Tl-S or Tl-Se interactions are considered to be bonds. In addition, the two compounds contain pairs of Tl{sup I} ions that interact through a closed-shell 'thallophilic' interaction: in the sulfur compound there are two inequivalent pairs of Tl atoms with Tl-Tl distances of 3.49 and 3.58 {angstrom}, while in the selenium compound those Tl-Tl interactions are at 3.54 and 3.63 {angstrom}.

36 MATERIALS SCIENCE↗
DOE OSTI2011

CONCERNING THE CLASSICAL CEPHEID VI{sub C} WESENHEIT FUNCTION'S STRONG METALLICITY DEPENDENCE

Evidence is presented which supports findings that the classical Cepheid VI{sub C} period Wesenheit function is relatively insensitive to metallicity. The viability of a recently advocated strong metallicity dependence was evaluated by applying the proposed correction ({gamma} = -0.8 mag dex{sup -1}) to distances established for the Magellanic Clouds via a Galactic VI{sub C} Wesenheit calibration, which is anchored to 10 nearby classical Cepheids with measured Hubble Space Telescope (HST) parallaxes. The resulting {gamma}-corrected distances for the Magellanic Clouds (e.g., Small Magellanic Cloud, {mu}{sub 0,{gamma}} {approx} 18.3) are in significant disagreement with that established from a mean of >300 published estimates (NED-D), and a universal Wesenheit template featuring 11 {delta} Scuti, SX Phe, RR Lyrae, and Type II Cepheid variables with HST/Hipparcos parallaxes. Conversely, adopting a null correction (i.e., {gamma} = 0 mag dex{sup -1}) consolidates the estimates. In tandem with existing evidence, the results imply that variations in chemical composition among Cepheids are a comparatively negligible source of uncertainty for W{sub VIc}-based extragalactic distances and determinations of H{sub 0}. A new approach is described which aims to provide additional Galactic Cepheid calibrators to facilitate subsequent assessments of the VI{sub C} Wesenheit function's relative (in) sensitivity to abundance changes. VVV/UKIDSS/Two Micron All Sky Survey JHK{sub s} photometry for clusters in spiral arms shall be employed to establish a precise galactic longitude-distance relation, which can be applied in certain cases to determine the absolute Wesenheit magnitudes for younger Cepheids.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

ARM Cloud Retrieval Ensemble Data Set (ACRED)

This document describes a new Atmospheric Radiation Measurement (ARM) data set, the ARM Cloud Retrieval Ensemble Data Set (ACRED), which is created by assembling nine existing ground-based cloud retrievals of ARM measurements from different cloud retrieval algorithms. The current version of ACRED includes an hourly average of nine ground-based retrievals with vertical resolution of 45 m for 512 layers. The techniques used for the nine cloud retrievals are briefly described in this document. This document also outlines the ACRED data availability, variables, and the nine retrieval products. Technical details about the generation of ACRED, such as the methods used for time average and vertical re-grid, are also provided.

54 ENVIRONMENTAL SCIENCES↗