92 research outputs found
Spallation Neutron Production by 0.8, 1.2 and 1.6 GeV Protons on various Targets
Spallation neutron production in proton induced reactions on Al, Fe, Zr, W,
Pb and Th targets at 1.2 GeV and on Fe and Pb at 0.8, and 1.6 GeV measured at
the SATURNE accelerator in Saclay is reported. The experimental
double-differential cross-sections are compared with calculations performed
with different intra-nuclear cascade models implemented in high energy
transport codes. The broad angular coverage also allowed the determination of
average neutron multiplicities above 2 MeV. Deficiencies in some of the models
commonly used for applications are pointed out.Comment: 20 pages, 32 figures, revised version, accepted fpr publication in
Phys. Rev.
Target Selection for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)
The Apache Point Observatory Galactic Evolution Experiment (APOGEE) is a
high-resolution infrared spectroscopic survey spanning all Galactic
environments (i.e., bulge, disk, and halo), with the principal goal of
constraining dynamical and chemical evolution models of the Milky Way. APOGEE
takes advantage of the reduced effects of extinction at infrared wavelengths to
observe the inner Galaxy and bulge at an unprecedented level of detail. The
survey's broad spatial and wavelength coverage enables users of APOGEE data to
address numerous Galactic structure and stellar populations issues. In this
paper we describe the APOGEE targeting scheme and document its various target
classes to provide the necessary background and reference information to
analyze samples of APOGEE data with awareness of the imposed selection criteria
and resulting sample properties. APOGEE's primary sample consists of ~100,000
red giant stars, selected to minimize observational biases in age and
metallicity. We present the methodology and considerations that drive the
selection of this sample and evaluate the accuracy, efficiency, and caveats of
the selection and sampling algorithms. We also describe additional target
classes that contribute to the APOGEE sample, including numerous ancillary
science programs, and we outline the targeting data that will be included in
the public data releases.Comment: Accepted to AJ. 31 pages, 11 figure
Measurement of the Proton and Deuteron Spin Structure Function g_1 in the Resonance Region
We have measured the proton and deuteron spin structure functions g_1^p and
g_1^d in the region of the nucleon resonances for W^2 < 5 GeV^2 and and GeV^2 by inelastically scattering 9.7 GeV polarized
electrons off polarized and targets. We observe
significant structure in g_1^p in the resonance region. We have used the
present results, together with the deep-inelastic data at higher W^2, to
extract . This is the first
information on the low-Q^2 evolution of Gamma toward the Gerasimov-Drell-Hearn
limit at Q^2 = 0.Comment: 7 pages, 2 figure
Precision Determination of the Neutron Spin Structure Function g1n
We report on a precision measurement of the neutron spin structure function
using deep inelastic scattering of polarized electrons by polarized
^3He. For the kinematic range 0.014<x<0.7 and 1 (GeV/c)^2< Q^2< 17 (GeV/c)^2,
we obtain at an average . We find relatively large negative
values for at low . The results call into question the usual Regge
theory method for extrapolating to x=0 to find the full neutron integral
, needed for testing quark-parton model and QCD sum rules.Comment: 5 pages, 3 figures To be published in Phys. Rev. Let
Planet Populations as a Function of Stellar Properties
Exoplanets around different types of stars provide a window into the diverse
environments in which planets form. This chapter describes the observed
relations between exoplanet populations and stellar properties and how they
connect to planet formation in protoplanetary disks. Giant planets occur more
frequently around more metal-rich and more massive stars. These findings
support the core accretion theory of planet formation, in which the cores of
giant planets form more rapidly in more metal-rich and more massive
protoplanetary disks. Smaller planets, those with sizes roughly between Earth
and Neptune, exhibit different scaling relations with stellar properties. These
planets are found around stars with a wide range of metallicities and occur
more frequently around lower mass stars. This indicates that planet formation
takes place in a wide range of environments, yet it is not clear why planets
form more efficiently around low mass stars. Going forward, exoplanet surveys
targeting M dwarfs will characterize the exoplanet population around the lowest
mass stars. In combination with ongoing stellar characterization, this will
help us understand the formation of planets in a large range of environments.Comment: Accepted for Publication in the Handbook of Exoplanet
Chemical Abundances of M-Dwarfs from the Apogee Survey. I. The Exoplanet Hosting Stars Kepler-138 and Kepler-186
We report the first detailed chemical abundance analysis of the exoplanet-hosting M-dwarf stars Kepler-138 and Kepler-186 from the analysis of high-resolution (R ⌠22,500) H-band spectra from the SDSS-IVâAPOGEE survey. Chemical abundances of 13 elementsâC, O, Na, Mg, Al, Si, K, Ca, Ti, V, Cr, Mn, and Feâare extracted from the APOGEE spectra of these early M-dwarfs via spectrum syntheses computed with an improved line list that takes into account H2O and FeH lines. This paper demonstrates that APOGEE spectra can be analyzed to determine detailed chemical compositions of M-dwarfs. Both exoplanet-hosting M-dwarfs display modest subsolar metallicities: [Fe/H]Kepler-138 = â0.09 ± 0.09 dex and [Fe/H]Kepler-186 = â0.08 ± 0.10 dex. The measured metallicities resulting from this high-resolution analysis are found to be higher by âŒ0.1â0.2 dex than previous estimates from lower-resolution spectra. The C/O ratios obtained for the two planet-hosting stars are near-solar, with values of 0.55 ± 0.10 for Kepler-138 and 0.52 ± 0.12 for Kepler-186. Kepler-186 exhibits a marginally enhanced [Si/Fe] ratio
Measurements of the Proton and Deuteron Spin Structure Functions and
Measurements are reported of the proton and deuteron spin structure functions g1 at beam energies of 29.1, 16.2, and 9.7 GeV and g2 at a beam energy of 29.1 GeV. The integrals of g1 over x have been evaluated at fixed Q**2 = 3 (GeV/c)**2 using the full data set. The Q**2 dependence of the ratio g1/F1 was studied and found to be small for Q**2 > 1 (GeV/c)**2. Within experimental precision the g2 data are well-described by the Wandzura-Wilczek twist-2 contribution. Twist-3 matrix elements were extracted and compared to theoretical predictions. The asymmetry A2 was measured and found to be significantly smaller than the positivity limit for both proton and deuteron targets. A2 for the proton is found to be positive and inconsistent with zero. Measurements of g1 in the resonance region show strong variations with x and Q**2, consistent with resonant amplitudes extracted from unpolarized data. These data allow us to study the Q**2 dependence of the first moments of g1 below the scaling region
Next-to-Leading Order QCD Analysis of Polarized Deep Inelastic Scattering Data
We present a Next-to-Leading order perturbative QCD analysis of world data on
the spin dependent structure functions , and , including
the new experimental information on the dependence of . Careful
attention is paid to the experimental and theoretical uncertainties. The data
constrain the first moments of the polarized valence quark distributions, but
only qualitatively constrain the polarized sea quark and gluon distributions.
The NLO results are used to determine the dependence of the ratio
and evolve the experimental data to a constant . We
determine the first moments of the polarized structure functions of the proton
and neutron and find agreement with the Bjorken sum rule.Comment: 21 pages, 4 figures; final version to be published in Phys. Lett. B.
References updated. Uses elsart.cls version 1996/04/22, 2e-1.4
The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
The Apache Point Observatory Galactic Evolution Experiment (APOGEE), one of the programs in the Sloan Digital Sky Survey III (SDSS-III), has now completed its systematic, homogeneous spectroscopic survey sampling all major populations of the Milky Way. After a three-year observing campaign on the Sloan 2.5 m Telescope, APOGEE has collected a half million high-resolution (R ~ 22,500), high signal-to-noise ratio (>100), infrared (1.51â1.70 ÎŒm) spectra for 146,000 stars, with time series information via repeat visits to most of these stars. This paper describes the motivations for the survey and its overall designâhardware, field placement, target selection, operationsâand gives an overview of these aspects as well as the data reduction, analysis, and products. An index is also given to the complement of technical papers that describe various critical survey components in detail. Finally, we discuss the achieved survey performance and illustrate the variety of potential uses of the data products by way of a number of science demonstrations, which span from time series analysis of stellar spectral variations and radial velocity variations from stellar companions, to spatial maps of kinematics, metallicity, and abundance patterns across the Galaxy and as a function of age, to new views of the interstellar medium, the chemistry of star clusters, and the discovery of rare stellar species. As part of SDSS-III Data Release 12 and later releases, all of the APOGEE data products are publicly available
The Eleventh and Twelfth Data Releases of the Sloan Digital Sky Survey: Final Data from SDSS-III
The third generation of the Sloan Digital Sky Survey (SDSS-III) took data from 2008 to 2014 using the original SDSS wide-field imager, the original and an upgraded multi-object fiber-fed optical spectrograph, a new near-infrared high-resolution spectrograph, and a novel optical interferometer. All of the data from SDSS-III are now made public. In particular, this paper describes Data Release 11 (DR11) including all data acquired through 2013 July, and Data Release 12 (DR12) adding data acquired through 2014 July (including all data included in previous data releases), marking the end of SDSS-III observing. Relative to our previous public release (DR10), DR12 adds one million new spectra of galaxies and quasars from the Baryon Oscillation Spectroscopic Survey (BOSS) over an additional 3000 deg2 of sky, more than triples the number of H-band spectra of stars as part of the Apache Point Observatory (APO) Galactic Evolution Experiment (APOGEE), and includes repeated accurate radial velocity measurements of 5500 stars from the Multi-object APO Radial Velocity Exoplanet Large-area Survey (MARVELS). The APOGEE outputs now include the measured abundances of 15 different elements for each star. In total, SDSS-III added 5200 deg2 of ugriz imaging; 155,520 spectra of 138,099 stars as part of the Sloan Exploration of Galactic Understanding and Evolution 2 (SEGUE-2) survey; 2,497,484 BOSS spectra of 1,372,737 galaxies, 294,512 quasars, and 247,216 stars over 9376 deg2; 618,080 APOGEE spectra of 156,593 stars; and 197,040 MARVELS spectra of 5513 stars. Since its first light in 1998, SDSS has imaged over 1/3 of the Celestial sphere in five bands and obtained over five million astronomical spectra. © 2015. The American Astronomical Society
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