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Schultheis M.,University of Nice Sophia Antipolis | Zasowski G.,Johns Hopkins University | Allende Prieto C.,Institute of Astrophysics of Canarias | Allende Prieto C.,University of La Laguna | And 18 more authors.
Astronomical Journal | Year: 2014

Galactic interstellar extinction maps are powerful and necessary tools for Milky Way structure and stellar population analyses, particularly toward the heavily reddened bulge and in the midplane. However, due to the difficulty of obtaining reliable extinction measures and distances for a large number of stars that are independent of these maps, tests of their accuracy and systematics have been limited. Our goal is to assess a variety of photometric stellar extinction estimates, including both two-dimensional and three-dimensional extinction maps, using independent extinction measures based on a large spectroscopic sample of stars toward the Milky Way bulge. We employ stellar atmospheric parameters derived from high-resolution H-band Apache Point Observatory Galactic Evolution Experiment (APOGEE) spectra, combined with theoretical stellar isochrones, to calculate line-of-sight extinction and distances for a sample of more than 2400 giants toward the Milky Way bulge. We compare these extinction values to those predicted by individual near-IR and near+mid-IR stellar colors, two-dimensional bulge extinction maps, and three-dimensional extinction maps. The long baseline, near+mid-IR stellar colors are, on average, the most accurate predictors of the APOGEE extinction estimates, and the two-dimensional and three-dimensional extinction maps derived from different stellar populations along different sightlines show varying degrees of reliability. We present the results of all of the comparisons and discuss reasons for the observed discrepancies. We also demonstrate how the particular stellar atmospheric models adopted can have a strong impact on this type of analysis, and discuss related caveats. © 2014. The American Astronomical Society. All rights reserved.

Nidever D.L.,University of Michigan | Bovy J.,Institute for Advanced Study | Bird J.C.,Vanderbilt University | Andrews B.H.,Ohio State University | And 44 more authors.
Astrophysical Journal | Year: 2014

We employ the first two years of data from the near-infrared, high-resolution SDSS-III/APOGEE spectroscopic survey to investigate the distribution of metallicity and α-element abundances of stars over a large part of the Milky Way disk. Using a sample of ≈10, 000 kinematically unbiased red-clump stars with ∼5% distance accuracy as tracers, the [α/Fe] versus [Fe/H] distribution of this sample exhibits a bimodality in [α/Fe] at intermediate metallicities, -0.9 < [Fe/H] <-0.2, but at higher metallicities ([Fe/H] ∼+0.2) the two sequences smoothly merge. We investigate the effects of the APOGEE selection function and volume filling fraction and find that these have little qualitative impact on the α-element abundance patterns. The described abundance pattern is found throughout the range 5 < R < 11 kpc and 0 < |Z| < 2 kpc across the Galaxy. The [α/Fe] trend of the high-α sequence is surprisingly constant throughout the Galaxy, with little variation from region to region (∼10%). Using simple galactic chemical evolution models, we derive an average star-formation efficiency (SFE) in the high-α sequence of ∼4.5 × 10-10 yr-1, which is quite close to the nearly constant value found in molecular-gas-dominated regions of nearby spirals. This result suggests that the early evolution of the Milky Way disk was characterized by stars that shared a similar star-formation history and were formed in a well-mixed, turbulent, and molecular-dominated ISM with a gas consumption timescale (SFE-1) of ∼2 Gyr. Finally, while the two α-element sequences in the inner Galaxy can be explained by a single chemical evolutionary track, this cannot hold in the outer Galaxy, requiring, instead, a mix of two or more populations with distinct enrichment histories. © 2014. The American Astronomical Society. All rights reserved.

Ross A.J.,University of Portsmouth | Percival W.J.,University of Portsmouth | Carnero A.,Observatorio Nacional | Carnero A.,Laboratorio Interinstitucional Of E Astronomia | And 41 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

We analyse the density field of 264 283 galaxies observed by the Sloan Digital Sky Survey (SDSS)-III Baryon Oscillation Spectroscopic Survey (BOSS) and included in the SDSS Data Release 9 (DR9). In total, the SDSS DR9 BOSS data include spectroscopic redshifts for over 400 000 galaxies spread over a footprint of more than 3000 deg2. We measure the power spectrum of these galaxies with redshifts 0.43 < z < 0.7 in order to constrain the amount of local non-Gaussianity, f localNL, in the primordial density field, paying particular attention to the impact of systematic uncertainties. The BOSS galaxy density field is systematically affected by the local stellar density and this influences the ability to accurately measure f local NL. In the absence of any correction, we find (erroneously) that the probability that f local NL is greater than zero, P(f local NL > 0), is 99.5 per cent. After quantifying and correcting for the systematic bias and including the added uncertainty, we find -45 < flocalNL < 195 at 95 per cent confidence and P(f localNL > 0) = 91.0 per cent. A more conservative approach assumes that we have only learnt the k dependence of the systematic bias and allows any amplitude for the systematic correction; we find that the systematic effect is not fully degenerate with that of f localNL, and we determine that -82 < flocalNL < 178 (at 95 per cent confidence) and P(f localNL > 0) = 68 per cent. This analysis demonstrates the importance of accounting for the impact of Galactic foregrounds on f local NL measurements. We outline the methods that account for these systematic biases and uncertainties. We expect our methods to yield robust constraints on f localNL for both our own and future large-scale structure investigations. © 2012 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society.

Schuler S.C.,National Optical Astronomy Observatory | Cunha K.,National Optical Astronomy Observatory | Cunha K.,University of Arizona | Smith V.V.,National Optical Astronomy Observatory | And 5 more authors.
Astrophysical Journal Letters | Year: 2011

Results of a detailed abundance analysis of the solar twins 16CygA and 16CygB based on high-resolution, high signal-to-noise ratio echelle spectroscopy are presented. 16CygB is known to host a giant planet while no planets have yet been detected around 16CygA. Stellar parameters are derived directly from our high-quality spectra, and the stars are found to be physically similar, with ΔT eff = +43K, Δlog g = -0.02dex, and Δξ = +0.10kms-1 (in the sense of A - B), consistent with previous findings. Abundances of 15 elements are derived and are found to be indistinguishable between the two stars. The abundances of each element differ by ≤0.026dex, and the mean difference is +0.003 ± 0.015 (σ)dex. Aside from Li, which has been previously shown to be depleted by a factor of at least 4.5 in 16CygB relative to 16CygA, the two stars appear to be chemically identical. The abundances of each star demonstrate a positive correlation with the condensation temperature of the elements (T c); the slopes of the trends are also indistinguishable. In accordance with recent suggestions, the positive slopes of the [m/H]-T c relations may imply that terrestrial planets have not formed around either 16CygA or 16CygB. The physical characteristics of the 16Cyg system are discussed in terms of planet formation models, and plausible mechanisms that can account for the lack of detected planets around 16CygA, the disparate Li abundances of 16CygA and B, and the eccentricity of the planet 16CygB b are suggested. © 2011. The American Astronomical Society. All rights reserved.

Comparat J.,Aix - Marseille University | Jullo E.,Aix - Marseille University | Kneib J.-P.,Aix - Marseille University | Kneib J.-P.,Ecole Polytechnique Federale de Lausanne | And 20 more authors.
Monthly Notices of the Royal Astronomical Society | Year: 2013

The baryon acoustic oscillation (BAO) feature in the two-point correlation function of galaxies supplies a standard ruler to probe the expansion history of the Universe. We study here several galaxy selection schemes, aiming at building an emission-line galaxy (ELG) sample in the redshift range 0.6 < z<1.7, that would be suitable for future BAO studies, providing a highly biased galaxy sample. We analyse the angular galaxy clustering of galaxy selections at the redshifts 0.5, 0.7, 0.8, 1 and 1.2 and we combine this analysis with a halo occupation distribution (HOD) model to derive the properties of the haloes these galaxies inhabit, in particular the galaxy bias on large scales. We also perform a weak lensing analysis (aperture statistics) to extract the galaxy bias and the cross-correlation coefficient and compare to theHODprediction. We apply this analysis on a data set composed of the photometry of the deep co-addition on Sloan Digital Sky Survey (SDSS) Stripe 82 (225 deg2), of Canada-France-Hawaii Telescope/Stripe 82 deep i-band weak lensing survey and of the Wide-Field Infrared Survey Explorer infrared photometric band W1. The analysis on the SDSS-III/constant mass galaxies selection at z = 0.5 is in agreement with previous studies on the tracer, moreover we measure its cross-correlation coefficient r = 1.16 ± 0.35. For the higher redshift bins, we confirm the trends that the brightest galaxy populations selected are strongly biased (b > 1.5), but we are limited by current data sets depth to derive precise values of the galaxy bias. A survey using such tracers of the mass field will guarantee a high significance detection of the BAO. © 2013 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society.

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