A. R. Walker - Semiconductor and Dimensional Metrology Division, National Institute of Standards and Technology, Gaithersburg, MD, USA

A. R. Walker
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Name
A. R. Walker
Affiliation
Semiconductor and Dimensional Metrology Division, National Institute of Standards and Technology, Gaithersburg, MD, USA
City
Gaithersburg
Country
United States

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Astrophysics of Galaxies (23)
 
Cosmology and Nongalactic Astrophysics (20)
 
Mathematics - Number Theory (6)
 
High Energy Astrophysical Phenomena (5)
 
Solar and Stellar Astrophysics (5)
 
Instrumentation and Methods for Astrophysics (4)
 
Physics - Materials Science (2)
 
Computer Science - Logic in Computer Science (1)
 
Mathematics - Geometric Topology (1)
 
Mathematics - Commutative Algebra (1)
 
Physics - Mesoscopic Systems and Quantum Hall Effect (1)
 
Computer Science - Learning (1)
 
Mathematics - Combinatorics (1)
 
Earth and Planetary Astrophysics (1)
 
Statistics - Machine Learning (1)
 
Computer Science - Software Engineering (1)
 
Computer Science - Programming Languages (1)

Publications Authored By A. R. Walker

Multi-wavelength CCD photometry over 21 years has been used to produce deep color-magnitude diagrams together with light curves for the variables in the Galactic globular cluster NGC 5824. Twenty-one new cluster RR Lyrae stars are identified, bringing the total to 47, of which 42 have reliable periods determined for the first time. The color-magnitude diagram is matched using BaSTI isochrones with age of $13$~Gyr. Read More

The Gauss circle problem concerns the difference $P_2(n)$ between the area of a circle of radius $\sqrt{n}$ and the number of lattice points it contains. In this paper, we study the Dirichlet series with coefficients $P_2(n)^2$, and prove that this series has meromorphic continuation to $\mathbb{C}$. Using this series, we prove that the Laplace transform of $P_2(n)^2$ satisfies $\int_0^\infty P_2(t)^2 e^{-t/X} \, dt = C X^{3/2} -X + O(X^{1/2+\epsilon})$, which gives a power-savings improvement to a previous result of Ivic. Read More

The generalized Gauss circle problem concerns the lattice point discrepancy of large spheres. In this paper, we study the Dirichlet series associated to $P_k(n)^2$, where $P_k(n)$ is the discrepancy between the volume of the $k$-dimensional sphere of radius $\sqrt{n}$ and the number of integer lattice points contained in that sphere. Using this Dirichlet series, we prove asymptotics with improved power-saving error terms for smoothed sums, including $\sum P_k(n)^2 e^{-n/X}$ and the Laplace transform $\int_0^\infty P_k(t)^2 e^{-t/X}dt$, in dimensions $k \geq 3$. Read More

We present the first results from the ongoing LAGER project (Lyman Alpha Galaxies in the Epoch of Reionization), which is the largest narrowband survey for $z\sim$ 7 galaxies to date. Using a specially built narrowband filter NB964 for the superb large-area Dark-Energy Camera (DECam) on the NOAO/CTIO 4m Blanco telescope, LAGER has collected 34 hours NB964 narrowband imaging data in the 3 deg$^2$ COSMOS field. We have identified 27 Lyman Alpha Emitter (LAE) candidates at $z=$ 6. Read More

We characterize the ability of the Dark Energy Camera (DECam) to perform relative astrometry across its 500~Mpix, 3 deg^2 science field of view, and across 4 years of operation. This is done using internal comparisons of ~4x10^7 measurements of high-S/N stellar images obtained in repeat visits to fields of moderate stellar density, with the telescope dithered to move the sources around the array. An empirical astrometric model includes terms for: optical distortions; stray electric fields in the CCD detectors; chromatic terms in the instrumental and atmospheric optics; shifts in CCD relative positions of up to ~10 um when the DECam temperature cycles; and low-order distortions to each exposure from changes in atmospheric refraction and telescope alignment. Read More

The classical 'Generalised von Neumann Theorem' is a central tool in the study of systems of linear equations with integer coefficients. This theorem reduces the task of counting weighted solutions of these equations to that of counting the weighted solutions for a particular family of forms, the Gowers norms $\Vert f \Vert_{U^{s+1}[N]}$ of the weight $f$. In this paper we consider the related study of systems of linear inequalities with real coefficients, and show that the number of solutions to such weighted Diophantine inequalities may also be bounded by Gowers norms, provided that the weights themselves are bounded. Read More

It has been known since Vinogradov that, for irrational $\alpha$, the sequence of fractional parts $\{\alpha p\}$ is equidistributed in $\mathbb{R}/\mathbb{Z}$ as $p$ ranges over primes. There is a natural second-order equidistribution property, a pair correlation of such fractional parts, which has recently received renewed interest, in particular regarding its relation to additive combinatorics. In this paper we show that the primes do not enjoy this stronger equidistribution property. Read More

Chemically peculiar stars in dwarf galaxies provide a window for exploring the birth environment of stars with varying chemical enrichment. We present a chemical abundance analysis of the brightest star in the newly discovered ultra-faint dwarf galaxy candidate Tucana III. Because it is particularly bright for a star in an ultra-faint Milky Way satellite, we are able to measure the abundance of 28 elements, including 13 neutron-capture species. Read More

We report the observation and physical characterization of the possible dwarf planet \UZ\ ("DeeDee"), a dynamically detached trans-Neptunian object discovered at 92 AU. This object is currently the second-most distant known trans-Neptunian object with reported orbital elements, surpassed in distance only by the dwarf planet Eris. The object was discovered with an $r$-band magnitude of 23. Read More

We present gravitational lens models of the multiply imaged quasar DES J0408-5354, recently discovered in the Dark Energy Survey (DES) footprint, with the aim of interpreting its remarkable quad-like configuration. We first model the DES single-epoch $grizY$ images as a superposition of a lens galaxy and four point-like objects, obtaining spectral energy distributions (SEDs) and relative positions for the objects. Three of the point sources (A,B,D) have SEDs compatible with the discovery quasar spectra, while the faintest point-like image (G2/C) shows significant reddening and a `grey' dimming of $\approx0. Read More

We report the discovery and spectroscopic confirmation of the quad-like lensed quasar system DES J0408-5354 found in the Dark Energy Survey (DES) Year 1 (Y1) data. This system was discovered during a search for DES Y1 strong lensing systems using a method that identified candidates as red galaxies with multiple blue neighbors. DES J0408-5354 consists of a central red galaxy surrounded by three bright (i < 20) blue objects and a fourth red object. Read More

Measurements of the galaxy stellar mass function are crucial to understand the formation of galaxies in the Universe. In a hierarchical clustering paradigm it is plausible that there is a connection between the properties of galaxies and their environments. Evidence for environmental trends has been established in the local Universe. Read More

The Large and Small Magellanic Clouds (LMC and SMC) are unique local laboratories for studying the formation and evolution of small galaxies in exquisite detail. The Survey of the MAgellanic Stellar History (SMASH) is an NOAO community DECam survey of the Clouds mapping 480 square degrees (distributed over ~2400 square degrees at ~20% filling factor) to ~24th mag in ugriz with the goal of identifying broadly distributed, low surface brightness stellar populations associated with the stellar halos and tidal debris of the Clouds. SMASH will also derive spatially-resolved star formation histories covering all ages out to large radii from the MCs that will further complement our understanding of their formation. Read More

We report the discovery of a stellar over-density 8$^{\circ}$ north of the center of the Small Magellanic Cloud (Small Magellanic Cloud Northern Over-Density; SMCNOD) using data from the first two years of the Dark Energy Survey (DES) and the first year of the MAGellanic SatelLITEs Survey (MagLiteS). The SMCNOD is indistinguishable in age, metallicity and distance from the nearby SMC stars, being primarly composed of intermediate-age stars (6 Gyr, Z=0.001), with a small fraction of young stars (1 Gyr, Z=0. Read More

In this paper the effect of weak lensing magnification on galaxy number counts is studied by cross-correlating the positions of two galaxy samples, separated by redshift, using data from the Dark Energy Survey Science Verification dataset. The analysis is carried out for two photometrically-selected galaxy samples, with mean photometric redshifts in the $0.2 < z < 0. Read More

ReLU neural networks define piecewise linear functions of their inputs. However, initializing and training a neural network is very different from fitting a linear spline. In this paper, we expand empirically upon previous theoretical work to demonstrate features of trained neural networks. Read More

The coalescence of a binary neutron star (BNS) pair is expected to produce gravitational waves (GW) and electromagnetic (EM) radiation, both of which may be detectable with currently available instruments. We describe a search for a theoretically predicted r-process optical transient from these mergers, dubbed the kilonova (KN), using griz broadband data from the Dark Energy Survey Supernova Program (DES-SN). Some models predict KNe to be redder, shorter-lived, and dimmer than supernovae (SNe), but at present the event rate of KNe is poorly constrained. Read More

We summarise our experience developing and using Termite, the first reactive synthesis tool intended for use by software development practitioners. We identify the main barriers to making reactive synthesis accessible to software developers and describe the key features of Termite designed to overcome these barriers, including an imperative C-like specification language, an interactive source-level debugger, and a user-guided code generator. Based on our experience applying Termite to synthesising real-world reactive software, we identify several caveats of the practical use of the reactive synthesis technology. Read More

We present a study of quasar selection using the DES supernova fields. We used a quasar catalog from an overlapping portion of the SDSS Stripe 82 region to quantify the completeness and efficiency of selection methods involving color, probabilistic modeling, variability, and combinations of color/probabilistic modeling with variability. We only considered objects that appear as point sources in the DES images. Read More

We search for excess gamma-ray emission coincident with the positions of confirmed and candidate Milky Way satellite galaxies using 6 years of data from the Fermi Large Area Telescope (LAT). Our sample of 45 stellar systems includes 28 kinematically confirmed dark-matter-dominated dwarf spheroidal galaxies (dSphs) and 17 recently discovered systems that have photometric characteristics consistent with the population of known dSphs. For each of these targets, the relative predicted gamma-ray flux due to dark matter annihilation is taken from kinematic analysis if available, and estimated from a distance-based scaling relation otherwise, assuming that the stellar systems are dark-matter-dominated dSphs. Read More

In this note we show that in a commutative ring $R$ with unity, for any $n > 0$, if $I$ is an $n$-absorbing ideal of $R$, then $(\sqrt{I})^{n} \subseteq I$. Read More

2016Oct
Authors: DESI Collaboration, Amir Aghamousa, Jessica Aguilar, Steve Ahlen, Shadab Alam, Lori E. Allen, Carlos Allende Prieto, James Annis, Stephen Bailey, Christophe Balland, Otger Ballester, Charles Baltay, Lucas Beaufore, Chris Bebek, Timothy C. Beers, Eric F. Bell, José Luis Bernal, Robert Besuner, Florian Beutler, Chris Blake, Hannes Bleuler, Michael Blomqvist, Robert Blum, Adam S. Bolton, Cesar Briceno, David Brooks, Joel R. Brownstein, Elizabeth Buckley-Geer, Angela Burden, Etienne Burtin, Nicolas G. Busca, Robert N. Cahn, Yan-Chuan Cai, Laia Cardiel-Sas, Raymond G. Carlberg, Pierre-Henri Carton, Ricard Casas, Francisco J. Castander, Jorge L. Cervantes-Cota, Todd M. Claybaugh, Madeline Close, Carl T. Coker, Shaun Cole, Johan Comparat, Andrew P. Cooper, M. -C. Cousinou, Martin Crocce, Jean-Gabriel Cuby, Daniel P. Cunningham, Tamara M. Davis, Kyle S. Dawson, Axel de la Macorra, Juan De Vicente, Timothée Delubac, Mark Derwent, Arjun Dey, Govinda Dhungana, Zhejie Ding, Peter Doel, Yutong T. Duan, Anne Ealet, Jerry Edelstein, Sarah Eftekharzadeh, Daniel J. Eisenstein, Ann Elliott, Stéphanie Escoffier, Matthew Evatt, Parker Fagrelius, Xiaohui Fan, Kevin Fanning, Arya Farahi, Jay Farihi, Ginevra Favole, Yu Feng, Enrique Fernandez, Joseph R. Findlay, Douglas P. Finkbeiner, Michael J. Fitzpatrick, Brenna Flaugher, Samuel Flender, Andreu Font-Ribera, Jaime E. Forero-Romero, Pablo Fosalba, Carlos S. Frenk, Michele Fumagalli, Boris T. Gaensicke, Giuseppe Gallo, Juan Garcia-Bellido, Enrique Gaztanaga, Nicola Pietro Gentile Fusillo, Terry Gerard, Irena Gershkovich, Tommaso Giannantonio, Denis Gillet, Guillermo Gonzalez-de-Rivera, Violeta Gonzalez-Perez, Shelby Gott, Or Graur, Gaston Gutierrez, Julien Guy, Salman Habib, Henry Heetderks, Ian Heetderks, Katrin Heitmann, Wojciech A. Hellwing, David A. Herrera, Shirley Ho, Stephen Holland, Klaus Honscheid, Eric Huff, Timothy A. Hutchinson, Dragan Huterer, Ho Seong Hwang, Joseph Maria Illa Laguna, Yuzo Ishikawa, Dianna Jacobs, Niall Jeffrey, Patrick Jelinsky, Elise Jennings, Linhua Jiang, Jorge Jimenez, Jennifer Johnson, Richard Joyce, Eric Jullo, Stéphanie Juneau, Sami Kama, Armin Karcher, Sonia Karkar, Robert Kehoe, Noble Kennamer, Stephen Kent, Martin Kilbinger, Alex G. Kim, David Kirkby, Theodore Kisner, Ellie Kitanidis, Jean-Paul Kneib, Sergey Koposov, Eve Kovacs, Kazuya Koyama, Anthony Kremin, Richard Kron, Luzius Kronig, Andrea Kueter-Young, Cedric G. Lacey, Robin Lafever, Ofer Lahav, Andrew Lambert, Michael Lampton, Martin Landriau, Dustin Lang, Tod R. Lauer, Jean-Marc Le Goff, Laurent Le Guillou, Auguste Le Van Suu, Jae Hyeon Lee, Su-Jeong Lee, Daniela Leitner, Michael Lesser, Michael E. Levi, Benjamin L'Huillier, Baojiu Li, Ming Liang, Huan Lin, Eric Linder, Sarah R. Loebman, Zarija Lukić, Jun Ma, Niall MacCrann, Christophe Magneville, Laleh Makarem, Marc Manera, Christopher J. Manser, Robert Marshall, Paul Martini, Richard Massey, Thomas Matheson, Jeremy McCauley, Patrick McDonald, Ian D. McGreer, Aaron Meisner, Nigel Metcalfe, Timothy N. Miller, Ramon Miquel, John Moustakas, Adam Myers, Milind Naik, Jeffrey A. Newman, Robert C. Nichol, Andrina Nicola, Luiz Nicolati da Costa, Jundan Nie, Gustavo Niz, Peder Norberg, Brian Nord, Dara Norman, Peter Nugent, Thomas O'Brien, Minji Oh, Knut A. G. Olsen, Cristobal Padilla, Hamsa Padmanabhan, Nikhil Padmanabhan, Nathalie Palanque-Delabrouille, Antonella Palmese, Daniel Pappalardo, Isabelle Pâris, Changbom Park, Anna Patej, John A. Peacock, Hiranya V. Peiris, Xiyan Peng, Will J. Percival, Sandrine Perruchot, Matthew M. Pieri, Richard Pogge, Jennifer E. Pollack, Claire Poppett, Francisco Prada, Abhishek Prakash, Ronald G. Probst, David Rabinowitz, Anand Raichoor, Chang Hee Ree, Alexandre Refregier, Xavier Regal, Beth Reid, Kevin Reil, Mehdi Rezaie, Constance M. Rockosi, Natalie Roe, Samuel Ronayette, Aaron Roodman, Ashley J. Ross, Nicholas P. Ross, Graziano Rossi, Eduardo Rozo, Vanina Ruhlmann-Kleider, Eli S. Rykoff, Cristiano Sabiu, Lado Samushia, Eusebio Sanchez, Javier Sanchez, David J. Schlegel, Michael Schneider, Michael Schubnell, Aurélia Secroun, Uros Seljak, Hee-Jong Seo, Santiago Serrano, Arman Shafieloo, Huanyuan Shan, Ray Sharples, Michael J. Sholl, William V. Shourt, Joseph H. Silber, David R. Silva, Martin M. Sirk, Anze Slosar, Alex Smith, George F. Smoot, Debopam Som, Yong-Seon Song, David Sprayberry, Ryan Staten, Andy Stefanik, Gregory Tarle, Suk Sien Tie, Jeremy L. Tinker, Rita Tojeiro, Francisco Valdes, Octavio Valenzuela, Monica Valluri, Mariana Vargas-Magana, Licia Verde, Alistair R. Walker, Jiali Wang, Yuting Wang, Benjamin A. Weaver, Curtis Weaverdyck, Risa H. Wechsler, David H. Weinberg, Martin White, Qian Yang, Christophe Yeche, Tianmeng Zhang, Gong-Bo Zhao, Yi Zheng, Xu Zhou, Zhimin Zhou, Yaling Zhu, Hu Zou, Ying Zu

DESI (Dark Energy Spectroscopic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations (BAO) and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. To trace the underlying dark matter distribution, spectroscopic targets will be selected in four classes from imaging data. We will measure luminous red galaxies up to $z=1. Read More

2016Oct
Authors: DESI Collaboration, Amir Aghamousa, Jessica Aguilar, Steve Ahlen, Shadab Alam, Lori E. Allen, Carlos Allende Prieto, James Annis, Stephen Bailey, Christophe Balland, Otger Ballester, Charles Baltay, Lucas Beaufore, Chris Bebek, Timothy C. Beers, Eric F. Bell, José Luis Bernal, Robert Besuner, Florian Beutler, Chris Blake, Hannes Bleuler, Michael Blomqvist, Robert Blum, Adam S. Bolton, Cesar Briceno, David Brooks, Joel R. Brownstein, Elizabeth Buckley-Geer, Angela Burden, Etienne Burtin, Nicolas G. Busca, Robert N. Cahn, Yan-Chuan Cai, Laia Cardiel-Sas, Raymond G. Carlberg, Pierre-Henri Carton, Ricard Casas, Francisco J. Castander, Jorge L. Cervantes-Cota, Todd M. Claybaugh, Madeline Close, Carl T. Coker, Shaun Cole, Johan Comparat, Andrew P. Cooper, M. -C. Cousinou, Martin Crocce, Jean-Gabriel Cuby, Daniel P. Cunningham, Tamara M. Davis, Kyle S. Dawson, Axel de la Macorra, Juan De Vicente, Timothée Delubac, Mark Derwent, Arjun Dey, Govinda Dhungana, Zhejie Ding, Peter Doel, Yutong T. Duan, Anne Ealet, Jerry Edelstein, Sarah Eftekharzadeh, Daniel J. Eisenstein, Ann Elliott, Stéphanie Escoffier, Matthew Evatt, Parker Fagrelius, Xiaohui Fan, Kevin Fanning, Arya Farahi, Jay Farihi, Ginevra Favole, Yu Feng, Enrique Fernandez, Joseph R. Findlay, Douglas P. Finkbeiner, Michael J. Fitzpatrick, Brenna Flaugher, Samuel Flender, Andreu Font-Ribera, Jaime E. Forero-Romero, Pablo Fosalba, Carlos S. Frenk, Michele Fumagalli, Boris T. Gaensicke, Giuseppe Gallo, Juan Garcia-Bellido, Enrique Gaztanaga, Nicola Pietro Gentile Fusillo, Terry Gerard, Irena Gershkovich, Tommaso Giannantonio, Denis Gillet, Guillermo Gonzalez-de-Rivera, Violeta Gonzalez-Perez, Shelby Gott, Or Graur, Gaston Gutierrez, Julien Guy, Salman Habib, Henry Heetderks, Ian Heetderks, Katrin Heitmann, Wojciech A. Hellwing, David A. Herrera, Shirley Ho, Stephen Holland, Klaus Honscheid, Eric Huff, Timothy A. Hutchinson, Dragan Huterer, Ho Seong Hwang, Joseph Maria Illa Laguna, Yuzo Ishikawa, Dianna Jacobs, Niall Jeffrey, Patrick Jelinsky, Elise Jennings, Linhua Jiang, Jorge Jimenez, Jennifer Johnson, Richard Joyce, Eric Jullo, Stéphanie Juneau, Sami Kama, Armin Karcher, Sonia Karkar, Robert Kehoe, Noble Kennamer, Stephen Kent, Martin Kilbinger, Alex G. Kim, David Kirkby, Theodore Kisner, Ellie Kitanidis, Jean-Paul Kneib, Sergey Koposov, Eve Kovacs, Kazuya Koyama, Anthony Kremin, Richard Kron, Luzius Kronig, Andrea Kueter-Young, Cedric G. Lacey, Robin Lafever, Ofer Lahav, Andrew Lambert, Michael Lampton, Martin Landriau, Dustin Lang, Tod R. Lauer, Jean-Marc Le Goff, Laurent Le Guillou, Auguste Le Van Suu, Jae Hyeon Lee, Su-Jeong Lee, Daniela Leitner, Michael Lesser, Michael E. Levi, Benjamin L'Huillier, Baojiu Li, Ming Liang, Huan Lin, Eric Linder, Sarah R. Loebman, Zarija Lukić, Jun Ma, Niall MacCrann, Christophe Magneville, Laleh Makarem, Marc Manera, Christopher J. Manser, Robert Marshall, Paul Martini, Richard Massey, Thomas Matheson, Jeremy McCauley, Patrick McDonald, Ian D. McGreer, Aaron Meisner, Nigel Metcalfe, Timothy N. Miller, Ramon Miquel, John Moustakas, Adam Myers, Milind Naik, Jeffrey A. Newman, Robert C. Nichol, Andrina Nicola, Luiz Nicolati da Costa, Jundan Nie, Gustavo Niz, Peder Norberg, Brian Nord, Dara Norman, Peter Nugent, Thomas O'Brien, Minji Oh, Knut A. G. Olsen, Cristobal Padilla, Hamsa Padmanabhan, Nikhil Padmanabhan, Nathalie Palanque-Delabrouille, Antonella Palmese, Daniel Pappalardo, Isabelle Pâris, Changbom Park, Anna Patej, John A. Peacock, Hiranya V. Peiris, Xiyan Peng, Will J. Percival, Sandrine Perruchot, Matthew M. Pieri, Richard Pogge, Jennifer E. Pollack, Claire Poppett, Francisco Prada, Abhishek Prakash, Ronald G. Probst, David Rabinowitz, Anand Raichoor, Chang Hee Ree, Alexandre Refregier, Xavier Regal, Beth Reid, Kevin Reil, Mehdi Rezaie, Constance M. Rockosi, Natalie Roe, Samuel Ronayette, Aaron Roodman, Ashley J. Ross, Nicholas P. Ross, Graziano Rossi, Eduardo Rozo, Vanina Ruhlmann-Kleider, Eli S. Rykoff, Cristiano Sabiu, Lado Samushia, Eusebio Sanchez, Javier Sanchez, David J. Schlegel, Michael Schneider, Michael Schubnell, Aurélia Secroun, Uros Seljak, Hee-Jong Seo, Santiago Serrano, Arman Shafieloo, Huanyuan Shan, Ray Sharples, Michael J. Sholl, William V. Shourt, Joseph H. Silber, David R. Silva, Martin M. Sirk, Anze Slosar, Alex Smith, George F. Smoot, Debopam Som, Yong-Seon Song, David Sprayberry, Ryan Staten, Andy Stefanik, Gregory Tarle, Suk Sien Tie, Jeremy L. Tinker, Rita Tojeiro, Francisco Valdes, Octavio Valenzuela, Monica Valluri, Mariana Vargas-Magana, Licia Verde, Alistair R. Walker, Jiali Wang, Yuting Wang, Benjamin A. Weaver, Curtis Weaverdyck, Risa H. Wechsler, David H. Weinberg, Martin White, Qian Yang, Christophe Yeche, Tianmeng Zhang, Gong-Bo Zhao, Yi Zheng, Xu Zhou, Zhimin Zhou, Yaling Zhu, Hu Zou, Ying Zu

DESI (Dark Energy Spectropic Instrument) is a Stage IV ground-based dark energy experiment that will study baryon acoustic oscillations and the growth of structure through redshift-space distortions with a wide-area galaxy and quasar redshift survey. The DESI instrument is a robotically-actuated, fiber-fed spectrograph capable of taking up to 5,000 simultaneous spectra over a wavelength range from 360 nm to 980 nm. The fibers feed ten three-arm spectrographs with resolution $R= \lambda/\Delta\lambda$ between 2000 and 5500, depending on wavelength. Read More

We use weak-lensing shear measurements to determine the mean mass of optically selected galaxy clusters in Dark Energy Survey Science Verification data. In a blinded analysis, we split the sample of more than 8,000 redMaPPer clusters into 15 subsets, spanning ranges in the richness parameter $5 \leq \lambda \leq 180$ and redshift $0.2 \leq z \leq 0. Read More

We prove that, if $x$ and $q\leqslant x^{1/16}$ are two parameters, then for any invertible residue class $a$ modulo $q$ there exists a product of exactly three primes, each one below $x^{1/3}$, that is congruent to $a$ modulo $q$. Read More

2016Sep
Affiliations: 1Department of Physics, Università di Roma Tor Vergata, 2NRC-Herzberg, Dominion Astrophysical Observatory, 3Department of Physics, Università di Roma Tor Vergata, 4INAF-Osservatorio Astronomico di Capodimonte, 5INAF-Osservatorio Astronomico di Roma, 6INAF-Osservatorio Astronomico di Bologna, 7Jeremiah Horrocks Institute of Astrophysics, University of Central Lancashire, 8INAF-Osservatorio Astronomico di Roma, 9Department of Physics and Astronomy, Iowa State University, 10Department of Physics and Astronomy, Iowa State University, 11European Southern Observatory, 12Department of Physics, Università di Roma Tor Vergata, 13National Optical Astronomy Observatory, 14INAF-Osservatorio Astronomico di Roma, 15INAF-Osservatorio Astronomico di Roma, 16INFN, Sezione di Pisa, 17INAF-Osservatorio Astronomico di Teramo, 18INAF-Osservatorio Astronomico di Teramo, 19Department of Astronomy & Astrophysics, University of Chicago, 20INAF-Osservatorio Astronomico di Roma, 21Sterrewacht Leiden, Leiden University, 22The Observatories of the Carnegie Institution for Science, 23INAF-Osservatorio Astronomico di Capodimonte, 24INAF-Osservatorio Astronomico di Roma, 25Kiso Observatory, Institute of Astronomy, School of Science, The University of Tokyo, 26Instituto de Astrofísica de Canarias, 27The Observatories of the Carnegie Institution for Science, 28INAF-Osservatorio Astronomico di Teramo, 29INAF-Osservatorio Astronomico di Teramo, 30INFN, Sezione di Pisa, 31INAF-Osservatorio Astronomico di Roma, 32Stellingwerf Consulting, 33INFN, Sezione di Pisa, 34Cerro Tololo Inter-American Observatory, National Optical Astronomy Observatory

New accurate and homogeneous optical UBVRI photometry has been obtained for variable stars in the Galactic globular $\omega$ Cen (NGC 5139). We secured 8202 CCD images covering a time interval of 24 years and a sky area of 84x48 arcmin. The current data were complemented with data available in the literature and provided new, homogeneous pulsation parameters (mean magnitudes, luminosity amplitudes,periods) for 187 candidate $\omega$ Cen RR Lyrae (RRLs). Read More

We report a new ultra-faint stellar system found in Dark Energy Camera data from the first observing run of the Magellanic Satellites Survey (MagLiteS). MagLiteS J0644-5953 (Pictor II or Pic II) is a low surface brightness ({\mu} = 28.5 mag arcsec$^{-2}$ within its half-light radius) resolved overdensity of old and metal-poor stars located at a heliocentric distance of 45 kpc. Read More

2016Sep
Affiliations: 1Saarland University, 2Graz University of Technology, 3University of Oxford, 4Graz University of Technology, 5Saarland University, 6Graz University of Technology, 7Saarland University, 8Data 61, CSIRO, 9Samsung Research America, 10Université Libre de Bruxelles, 11Université Libre de Bruxelles, 12Samsung Research America, 13CNRS, Irisa, 14Johannes-Kepler-University Linz, 15Saarland University, 16Independent Researcher

We report on the benchmarks, participants and results of the third reactive synthesis competition(SYNTCOMP 2016). The benchmark library of SYNTCOMP 2016 has been extended to benchmarks in the new LTL-based temporal logic synthesis format (TLSF), and 2 new sets of benchmarks for the existing AIGER-based format for safety specifications. The participants of SYNTCOMP 2016 can be separated according to these two classes of specifications, and we give an overview of the 6 tools that entered the competition in the AIGER-based track, and the 3 participants that entered the TLSF-based track. Read More

The ray graph is a Gromov hyperbolic graph on which the mapping class group of the plane minus a Cantor set acts by isometries. We give a description of the Gromov boundary of the ray graph in terms of cliques of long rays on the plane minus a Cantor set. As a consequence, we prove that the Gromov boundary of the ray graph is homeomorphic to a quotient of a subset of the circle. Read More

We present the identification of 634 variable stars in the Milky Way dSph satellite Sculptor based on archival ground-based optical observations spanning $\sim$24 years and covering $\sim$ 2.5 deg$^2$. We employed the same methodologies as the "Homogeneous Photometry" series published by Stetson. Read More

We present new radial velocity (RV) measurements of old (horizontal branch) and intermediate-age (red clump) stellar tracers in the Carina dwarf spheroidal. They are based on more than 2,200 low-resolution spectra collected with VIMOS at VLT. The targets are faint (20Read More

The correlation between active galactic nuclei (AGN) and environment provides important clues to AGN fueling and the relationship of black hole growth to galaxy evolution. In this paper, we analyze the fraction of galaxies in clusters hosting AGN as a function of redshift and cluster richness for X-ray detected AGN associated with clusters of galaxies in Dark Energy Survey (DES) Science Verification data. The present sample includes 33 AGN with L_X > 10^43 ergs s^-1 in non-central, host galaxies with luminosity greater than 0. Read More

2016Jun

We report the results of a Dark Energy Camera (DECam) optical follow-up of the gravitational wave (GW) event GW151226, discovered by the Advanced LIGO detectors. Our observations cover 28.8 deg$^2$ of the localization region in the $i$ and $z$ bands (containing 3% of the BAYESTAR localization probability), starting 10 hours after the event was announced and spanning four epochs at $2-24$ days after the GW detection. Read More

2016Jun

The construction of the KAT-7 array in the Karoo region of the Northern Cape in South Africa was intended primarily as an engineering prototype for technologies and techniques applicable to the MeerKAT telescope. This paper looks at the main engineering and scien- tific highlights from this effort, and discusses their applicability to both MeerKAT and other next-generation radio telescopes. In particular we found that the composite dish surface works well, but it becomes complicated to fabricate for a dish lacking circular symmetry; the Stir- ling cycle cryogenic system with ion pump to achieve vacuum works but demands much higher maintenance than an equivalent Gifford-McMahon cycle system; the ROACH (Recon- figurable Open Architecture Computing Hardware)-based correlator with SPEAD (Stream- ing Protocol for Exchanging Astronomical Data) protocol data transfer works very well and KATCP (Karoo Array Telescope Control Protocol) control protocol has proven very flexible and convenient. Read More

We extend the axiomatization for detecting and quantifying sign changes of Meher and Murty to sequences of complex numbers. We further generalize this result when the sequence is comprised of the coefficients of an $L$-function. As immediate applications, we prove that there are sign changes in intervals within sequences of coefficients of GL(2) holomorphic cusp forms, GL(2) Maass forms, and GL(3) Maass forms. Read More

We study the Sunyaev-Zel'dovich effect (SZE) signature in South Pole Telescope (SPT) data for an ensemble of 719 optically identified galaxy clusters selected from 124.6 deg$^2$ of the Dark Energy Survey (DES) science verification data, detecting a stacked SZE signal down to richness $\lambda\sim20$. The SZE signature is measured using matched-filtered maps of the 2500 deg$^2$ SPT-SZ survey at the positions of the DES clusters, and the degeneracy between SZE observable and matched-filter size is broken by adopting as priors SZE and optical mass-observable relations that are either calibrated using SPT selected clusters or through the Arnaud et al. Read More

Structural, interfacial, optical, and transport properties of large-area MoS2 ultra-thin films on BN-buffered silicon substrates fabricated using magnetron sputtering are investigated. A relatively simple growth strategy is demonstrated here that simultaneously promotes superior interfacial and bulk MoS2 properties. Few layers of MoS2 are established using X-ray reflectivity, diffraction, ellipsometry, and Raman spectroscopy measurements. Read More

We report the discovery of an optical Einstein Ring in the Sculptor constellation, IAC J010127-334319, in the vicinity of the Sculptor Dwarf Spheroidal Galaxy. It is an almost complete ring ($\sim 300^{\circ}$) with a diameter of $\sim 4.5\, {\rm arcsec}$. Read More

Galaxies and their dark matter halos populate a complicated filamentary network around large, nearly empty regions known as cosmic voids. Cosmic voids are usually identified in spectroscopic galaxy surveys, where 3D information about the large-scale structure of the Universe is available. Although an increasing amount of photometric data is being produced, its potential for void studies is limited since photometric redshifts induce line-of-sight position errors of $\sim50$ Mpc/$h$ or more that can render many voids undetectable. Read More