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Spontaneous IPSCs and glycine receptors with slow kinetics in wide-field amacrine cells in the mature rat retina

Veruki, Margaret Lin; Gill, Silje Bakken; Hartveit, Espen
Fonte: Blackwell Science Inc Publicador: Blackwell Science Inc
Tipo: Artigo de Revista Científica
Português
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The functional properties of glycine receptors were analysed in different types of wide-field amacrine cells, narrowly stratifying cells considered to play a role in larger-scale integration across the retina. The patch-clamp technique was used to record spontaneous IPSCs (spIPSCs) and glycine-evoked patch responses from mature rat retinal slices (4–7 weeks postnatal). Glycinergic spIPSCs were blocked reversibly by strychnine (300 nm). Compared to previously described spIPSCs in AII amacrine cells, the spIPSCs in wide-field amacrine cells displayed a very slow decay time course (τfast ∼ 15 ms; τslow ∼ 57 ms). The kinetic properties of spIPSCs in whole-cell recordings were paralleled by even slower deactivation kinetics of responses evoked by brief pulses of glycine (3 mm) to outside-out patches from wide-field amacrine cells (τfast ∼ 45 ms; τslow ∼ 350 ms). Non-stationary noise analysis of patch responses and spIPSCs yielded similar average single-channel conductances (∼31 and ∼34 pS, respectively). Similar, as well as both lower- and higher-conductance levels could be identified from directly observed single-channel gating during the decay phase of spIPSCs and patch responses. These results suggest that the slow glycinergic spIPSCs in wide-field amacrine cells involve α2β heteromeric receptors. Taken together with previous work...

Wide-Field Motion Integration in Fly VS Cells: Insights from an Inverse Approach

Torben-Nielsen, Benjamin; Stiefel, Klaus M.
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Português
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Fly lobula plate tangential cells are known to perform wide-field motion integration. It is assumed that the shape of these neurons, and in particular the shape of the subclass of VS cells, is responsible for this type of computation. We employed an inverse approach to investigate the morphology-function relationship underlying wide-field motion integration in VS cells. In the inverse approach detailed, model neurons are optimized to perform a predefined computation: here, wide-field motion integration. We embedded the model neurons to be optimized in a biologically plausible model of fly motion detection to provide realistic inputs, and subsequently optimized model neuron with and without active conductances (gNa, gK, gK(Na)) along their dendrites to perform this computation. We found that both passive and active optimized model neurons perform well as wide-field motion integrators. In addition, all optimized morphologies share the same blueprint as real VS cells. In addition, we also found a recurring blueprint for the distribution of gK and gNa in the active models. Moreover, we demonstrate how this morphology and distribution of conductances contribute to wide-field motion integration. As such, by using the inverse approach we can predict the still unknown distribution of gK and gNa and their role in motion integration in VS cells.

Lensfree Fluorescent On-Chip Imaging of Transgenic Caenorhabditis elegans Over an Ultra-Wide Field-of-View

Coskun, Ahmet F.; Sencan, Ikbal; Su, Ting-Wei; Ozcan, Aydogan
Fonte: Public Library of Science Publicador: Public Library of Science
Tipo: Artigo de Revista Científica
Publicado em 06/01/2011 Português
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We demonstrate lensfree on-chip fluorescent imaging of transgenic Caenorhabditis elegans (C. elegans) over an ultra-wide field-of-view (FOV) of e.g., >2–8 cm2 with a spatial resolution of ∼10µm. This is the first time that a lensfree on-chip platform has successfully imaged fluorescent C. elegans samples. In our wide-field lensfree imaging platform, the transgenic samples are excited using a prism interface from the side, where the pump light is rejected through total internal reflection occurring at the bottom facet of the substrate. The emitted fluorescent signal from C. elegans samples is then recorded on a large area opto-electronic sensor-array over an FOV of e.g., >2–8 cm2, without the use of any lenses, thin-film interference filters or mechanical scanners. Because fluorescent emission rapidly diverges, such lensfree fluorescent images recorded on a chip look blurred due to broad point-spread-function of our platform. To combat this resolution challenge, we use a compressive sampling algorithm to uniquely decode the recorded lensfree fluorescent patterns into higher resolution images, demonstrating ∼10 µm resolution. We tested the efficacy of this compressive decoding approach with different types of opto-electronic sensors to achieve a similar resolution level...

Adaptive optics scanning laser ophthalmoscope with integrated wide-field retinal imaging and tracking

Ferguson, R. Daniel; Zhong, Zhangyi; Hammer, Daniel X.; Mujat, Mircea; Patel, Ankit H.; Deng, Cong; Zou, Weiyao; Burns, Stephen A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/11/2010 Português
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We have developed a new, unified implementation of the adaptive optics scanning laser ophthalmoscope (AOSLO) incorporating a wide-field line-scanning ophthalmoscope (LSO) and a closed-loop optical retinal tracker. AOSLO raster scans are deflected by the integrated tracking mirrors so that direct AOSLO stabilization is automatic during tracking. The wide-field imager and large-spherical-mirror optical interface design, as well as a large-stroke deformable mirror (DM), enable the AOSLO image field to be corrected at any retinal coordinates of interest in a field of >25 deg. AO performance was assessed by imaging individuals with a range of refractive errors. In most subjects, image contrast was measurable at spatial frequencies close to the diffraction limit. Closed-loop optical (hardware) tracking performance was assessed by comparing sequential image series with and without stabilization. Though usually better than 10 μm rms, or 0.03 deg, tracking does not yet stabilize to single cone precision but significantly improves average image quality and increases the number of frames that can be successfully aligned by software-based post-processing methods. The new optical interface allows the high-resolution imaging field to be placed anywhere within the wide field without requiring the subject to re-fixate...

Wide-field Functional Imaging of Blood Flow and Hemoglobin Oxygen Saturation in the Rodent Dorsal Window Chamber

Moy, Austin J.; White, Sean M.; Indrawan, Elmer S.; Lotfi, Justin; Nudelman, Matthew J.; Costantini, Samantha J.; Agarwal, Nikita; Jia, Wangcun; Kelly, Kristen M.; Sorg, Brian S.; Choi, Bernard
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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The rodent dorsal window chamber is a widely used in vivo model of the microvasculature. The model consists of a 1cm region of exposed microvasculature in the rodent dorsal skin that is immobilized by surgically implanted titanium frames, allowing the skin microvasculature to be visualized. We describe a detailed protocol for surgical implantation of the dorsal window chamber which enables researchers to perform the window chamber implantation surgery. We further describe subsequent wide-field functional imaging of the chamber to obtain hemodynamic information in the form of blood oxygenation and blood flow on a cm size region of interest. Optical imaging techniques, such as intravital microscopy, have been applied extensively to the dorsal window chamber to study microvascular-related disease and conditions. Due to the limited field of view of intravital microscopy, detailed hemodynamic information typically is acquired from small regions of interest, typically on the order of hundreds of μm. The wide-field imaging techniques described herein complement intravital microscopy, allowing researchers to obtain hemodynamic information at both microscopic and macroscopic spatial scales. Compared with intravital microscopy, wide-field functional imaging requires simple instrumentation...

Optical sectioning by wide-field photobleaching imprinting microscopy

Li, Chiye; Gao, Liang; Liu, Yan; Wang, Lihong V.
Fonte: AIP Publishing LLC Publicador: AIP Publishing LLC
Tipo: Artigo de Revista Científica
Português
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We present a generic wide-field optical sectioning scheme, photobleaching imprinting microscopy (PIM), for depth-resolved cross-sectional fluorescence imaging. Wide-field PIM works by extracting a nonlinear component that depends on the excitation fluence as a result of photobleaching-induced fluorescence decay. Since no specific fluorescent dyes or illumination modules are required, wide-field PIM is easy to implement on a standard microscope. Moreover, wide-field PIM is superior to deconvolution microscopy in removing background fluorescence, yielding a six-fold improvement in image contrast.

Foregrounds in wide-field redshifted 21 cm power spectra

Thyagarajan, Nithyanandan; Jacobs, Daniel C.; Bowman, Judd D.; Barry, N.; Beardsley, A. P.; Bernardi, G.; Briggs, F.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; Oliveira-Costa, A. de; Dillon, Joshua S.; Emrich, D.; Ewall-Wice, A.; Feng, L.; Goeke, R.; Gr
Fonte: American Astronomical Society Publicador: American Astronomical Society
Tipo: Artigo de Revista Científica
Português
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Detection of 21 cm emission of H i from the epoch of reionization, at redshifts $z\gt 6$, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the H i signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic pitchfork signature on the "foreground wedge" in Fourier delay space. Based on these results...

The Wide Field Imager Lyman-Alpha Search (WFILAS) for Galaxies at Redshift ~ 5.7. II. Survey design and sample analysis

Westra, Eduard; Jones, D Heath; Lidman, Christopher; Meisenheimer, Klaus; Athreya, Ramana M; Wolf, Christian; Szeifert, Thomas; Pompei, Emanuela; Vanzi, Leonardo
Fonte: Springer Publicador: Springer
Tipo: Artigo de Revista Científica
Português
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Context. Wide-field narrowband surveys are an efficient way of searching large volumes of high-redshift space for distant galaxies. Aims. We describe the Wide Field Imager Lyman-Alpha Search (WFILAS) over 0.74 sq. degree for bright emission-line galaxies

The Wide Field Spectrograph (WiFeS)

Dopita, Michael; Hart, John; McGregor, Peter; Oates, Paddy; Bloxham, Gabe; Jones, Damian
Fonte: Kluwer Academic Publishers Publicador: Kluwer Academic Publishers
Tipo: Artigo de Revista Científica
Português
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This paper describes the Wide Field Spectrograph (WiFeS) under construction at the Research School of Astronomy and Astrophysics (RSAA) of the Australian National University (ANU) for the ANU 2.3 m telescope at the Siding Spring Observatory. WiFeS is a po

Revisiting the theory of interferometric wide-field synthesis

Pety, Jérôme; Rodriguez-Fernandez, Nemesio J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 26/04/2010 Português
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After several generations of interferometers in radioastronomy, wide-field imaging at high angular resolution is today a major goal for trying to match optical wide-field performances. All the radio-interferometric, wide-field imaging methods currently belong to the mosaicking family. Based on a 30 years old, original idea from Ekers & Rots, we aim at proposing an alternate formalism. Starting from their ideal case, we successively evaluate the impact of the standard ingredients of interferometric imaging. A comparison with standard nonlinear mosaicking shows that both processing schemes are not mathematically equivalent, though they both recover the sky brightness. In particular, the weighting scheme is very different in both methods. Moreover, the proposed scheme naturally processes the short spacings from both single-dish antennas and heterogeneous arrays. Finally, the sky gridding of the measured visibilities, required by the proposed scheme, may potentially save large amounts of hard-disk space and cpu processing power over mosaicking when handling data sets acquired with the on-the-fly observing mode. We propose to call this promising family of imaging methods wide-field synthesis because it explicitly synthesizes visibilities at a much finer spatial frequency resolution than the one set by the diameter of the interferometer antennas.; Comment: 22 pages...

Wide Field X-ray Telescope: Mission Overview

Rosati, P.; Borgani, S.; Gilli, R.; Paolillo, M.; Tozzi, P.; Murray, S.; Giacconi, R.; Ptak, A.; Weisskopf, M.; Forman, W.; Jones, C.; Team, the WFXT
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 29/10/2010 Português
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The Wide Field X-Ray Telescope (WFXT) is a medium-class mission designed to be 2-orders-of-magnitude more sensitive than any previous or planned X-ray mission for large area surveys and to match in sensitivity the next generation of wide-area optical, IR and radio surveys. Using an innovative wide-field X-ray optics design, WFXT provides a field of view of 1 square degree (10 times Chandra) with an angular resolution of 5" (Half Energy Width, HEW) nearly constant over the entire field of view, and a large collecting area (up to 1 m^2 at 1 keV, > 10x Chandra) over the 0.1-7 keV band. WFXTs low-Earth orbit also minimizes the particle background. In five years of operation, WFXT will carry out three extragalactic surveys at unprecedented depth and address outstanding questions in astrophysics, cosmology and fundamental physics. In this article, we illustrate the mission concept and the connection between science requirements and mission parameters.; Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in Bologna, Italy, Nov. 25-26 2009. To appear in Memorie della Societ\`a Astronomica Italiana 2010 (arXiv:1010.5889)

Interferometric imaging with the 32 element Murchison Wide-field Array

Ord, S. M.; Mitchell, D. A.; Wayth, R. B.; Greenhill, L. J.; Bernardi, G.; Gleadow, S.; Edgar, R. G.; Clark, M. A.; Allen, G.; Arcus, W.; Benkevitch, L.; Bowman, J. D.; Briggs, F. H.; Bunton, J. D.; Burns, S.; Cappallo, R. J.; Coles, W. A.; Corey, B. E.;
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 08/10/2010 Português
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The Murchison Wide-field Array (MWA) is a low frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of re-ionisation (EOR) and to probe the structure of the solar corona. Sited in Western Australia, the full MWA will comprise 8192 dipoles grouped into 512 tiles, and be capable of imaging the sky south of 40 degree declination, from 80 MHz to 300 MHz with an instantaneous field of view that is tens of degrees wide and a resolution of a few arcminutes. A 32-station prototype of the MWA has been recently commissioned and a set of observations taken that exercise the whole acquisition and processing pipeline. We present Stokes I, Q, and U images from two ~4 hour integrations of a field 20 degrees wide centered on Pictoris A. These images demonstrate the capacity and stability of a real-time calibration and imaging technique employing the weighted addition of warped snapshots to counter extreme wide field imaging distortions.; Comment: Accepted for publication in PASP. This is the draft before journal typesetting corrections and proofs so does contain formatting and journal style errors, also has with lower quality figures for space requirements

EVLA Observations of Galactic Supernova Remnants: Wide-field Continuum and Spectral-index Imaging

Bhatnagar, S.; Rau, U.; Green, D. A.; Rupen, M. P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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The radio continuum emission from the Galaxy has a rich mix of thermal and non-thermal emission. This very richness makes their interpretation challenging since the low radio opacity means that a radio image represents the sum of all emission regions along the line-of-sight. These challenges make the existing narrow-band radio surveys of the Galactic plane difficult to interpret: e.g. a small region of emission might be a supernova remnant (SNR) or an HII region, or a complex combination of both. Instantaneous wide bandwidth radio observations in combination with the capability for high resolution spectral index mapping, can be directly used to disentangle these effects. Here we demonstrate simultaneous continuum and spectral index imaging capability at the full continuum sensitivity and resolution using newly developed wide-band wide-field imaging algorithms. Observations were done in the L- and C-Band with a total bandwidth of 1 and 2 GHz respectively. We present preliminary results in the form of a full-field continuum image covering the wide-band sensitivity pattern of the EVLA centered on a large but poorly studied SNR (G55.7+3.4) and relatively narrower field continuum and spectral index maps of three fields containing SNR and diffused thermal emission. We demonstrate that spatially resolved spectral index maps differentiates regions with emission of different physical origin (spectral index variation across composite SNRs and separation of thermal and non-thermal emission)...

Wide-Field InfrarRed Survey Telescope-Astrophysics Focused Telescope Assets WFIRST-AFTA 2015 Report

Spergel, D.; Gehrels, N.; Baltay, C.; Bennett, D.; Breckinridge, J.; Donahue, M.; Dressler, A.; Gaudi, B. S.; Greene, T.; Guyon, O.; Hirata, C.; Kalirai, J.; Kasdin, N. J.; Macintosh, B.; Moos, W.; Perlmutter, S.; Postman, M.; Rauscher, B.; Rhodes, J.; Wa
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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This report describes the 2014 study by the Science Definition Team (SDT) of the Wide-Field Infrared Survey Telescope (WFIRST) mission. It is a space observatory that will address the most compelling scientific problems in dark energy, exoplanets and general astrophysics using a 2.4-m telescope with a wide-field infrared instrument and an optical coronagraph. The Astro2010 Decadal Survey recommended a Wide Field Infrared Survey Telescope as its top priority for a new large space mission. As conceived by the decadal survey, WFIRST would carry out a dark energy science program, a microlensing program to determine the demographics of exoplanets, and a general observing program utilizing its ultra wide field. In October 2012, NASA chartered a Science Definition Team (SDT) to produce, in collaboration with the WFIRST Study Office at GSFC and the Program Office at JPL, a Design Reference Mission (DRM) for an implementation of WFIRST using one of the 2.4-m, Hubble-quality telescope assemblies recently made available to NASA. This DRM builds on the work of the earlier WFIRST SDT, reported by Green et al. (2012) and the previous WFIRST-2.4 DRM, reported by Spergel et. (2013). The 2.4-m primary mirror enables a mission with greater sensitivity and higher angular resolution than the 1.3-m and 1.1-m designs considered previously...

Science with a wide-field UV transient explorer

Sagiv, I.; Gal-Yam, A.; Ofek, E. O.; Waxman, E.; Aharonson, O.; Nakar, E.; Maoz, D.; Trakhtenbrot, B.; Kulkarni, S. R.; Phinney, E. S.; Topaz, J.; Beichman, C.; Murthy, J.; Worden, S. P.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/03/2013 Português
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The time-variable electromagnetic sky has been well-explored at a wide range of wavelengths. Numerous high-energy space missions take advantage of the dark Gamma-ray and X-ray sky and utilize very wide field detectors to provide almost continuous monitoring of the entire celestial sphere. In visible light, new wide-field ground-based surveys cover wide patches of sky with ever decreasing cadence, progressing from monthly-weekly time scale surveys to sub-night sampling. In the radio, new powerful instrumentation offers unprecedented sensitivity over wide fields of view, with pathfinder experiments for even more ambitious programs underway. In contrast, the ultra-violet (UV) variable sky is relatively poorly explored, even though it offers exciting scientific prospects. Here, we review the potential scientific impact of a wide-field UV survey on the study of explosive and other transient events, as well as known classes of variable objects, such as active galactic nuclei and variable stars. We quantify our predictions using a fiducial set of observational parameters which are similar to those envisaged for the proposed ULTRASAT mission. We show that such a mission would be able to revolutionize our knowledge about massive star explosions by measuring the early UV emission from hundreds of events...

Wide-field VLBI Imaging

Garrett, M. A.; Porcas, R. W.; Pedlar, A.; Muxlow, T. W. B.; Garrington, S. T.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/06/1999 Português
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We discuss the technique of Wide-field imaging as it applies to Very Long Baseline Interferometry (VLBI). In the past VLBI data sets were usually averaged so severely that the field-of-view was typically restricted to regions extending a few hundred milliarcseconds from the phase centre of the field. Recent advances in data analysis techniques, together with increasing data storage capabilities, and enhanced computer processing power, now permit VLBI images to be made whose angular size represents a significant fraction of an individual antenna's primary beam. This technique has recently been successfully applied to several large separation gravitational lens systems, compact Supernova Remnants in the starburst galaxy M82, and two faint radio sources located within the same VLA FIRST field. It seems likely that other VLBI observing programmes might benefit from this wide-field approach to VLBI data analysis. With the raw sensitivity of global VLBI set to improve by a factor 4-5 over the coming few years, the number of sources that can be detected in a given field will rise considerably. In addition, a continued progression in VLBI's ability to image relatively faint and extended low brightness temperature features (such as hot-spots in large-scale astrophysical jets) is also to be expected. As VLBI sensitivity approaches the $\mu$Jy level...

Wide-field VLBA Observations of the Chandra Deep Field South

Middelberg, Enno; Deller, Adam; Morgan, John; Rottmann, Helge; Alef, Walter; Tingay, Steven; Norris, Ray; Bach, Uwe; Brisken, Walter; Lenc, Emil
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/11/2010 Português
Relevância na Pesquisa
46.86391%
Wide-field surveys are a commonly-used method for studying thousands of objects simultaneously, to investigate, e.g., the joint evolution of star-forming galaxies and active galactic nuclei. VLBI observations can yield valuable input to such studies because they are able to identify AGN. However, VLBI observations of large swaths of the sky are impractical using standard methods, because the fields of view of VLBI observations are of the order of 10" or less. We have embarked on a project to carry out Very Long Baseline Array (VLBA) observations of all 96 known radio sources in one of the best-studied areas in the sky, the Chandra Deep Field South (CDFS). The challenge was to develop methods which could significantly reduce the amount of observing (and post-processing) time. We have developed an extension to the DiFX software correlator which allows one to correlate hundreds of positions within the primary beams. This extension enabled us to target many sources, at full resolution and high sensitivity, using only a small amount of observing time. The combination of wide fields-of-view and high sensitivity across the field in this survey is unprecedented. We have observed with the VLBA a single pointing containing the Chandra Deep Field South...

Design drivers for a wide-field multi-object spectrograph for the William Herschel Telescope

Balcells, Marc; Benn, Chris R.; Carter, David; Dalton, Gavin B.; Trager, Scott C.; Feltzing, Sofia; Verheijen, Marc A. W.; Jarvis, Matt; Percival, Will; Abrams, Don C.; Agocs, Tibor; Brown, Anthony G. A.; Cano, Diego; Evans, Chris; Helmi, Amina; Lewis, Ia
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 03/08/2010 Português
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Wide-field multi-object spectroscopy is a high priority for European astronomy over the next decade. Most 8-10m telescopes have a small field of view, making 4-m class telescopes a particularly attractive option for wide-field instruments. We present a science case and design drivers for a wide-field multi-object spectrograph (MOS) with integral field units for the 4.2-m William Herschel Telescope (WHT) on La Palma. The instrument intends to take advantage of a future prime-focus corrector and atmospheric-dispersion corrector that will deliver a field of view 2 deg in diameter, with good throughput from 370 to 1,000 nm. The science programs cluster into three groups needing three different resolving powers R: (1) high-precision radial-velocities for Gaia-related Milky Way dynamics, cosmological redshift surveys, and galaxy evolution studies (R = 5,000), (2) galaxy disk velocity dispersions (R = 10,000) and (3) high-precision stellar element abundances for Milky Way archaeology (R = 20,000). The multiplex requirements of the different science cases range from a few hundred to a few thousand, and a range of fibre-positioner technologies are considered. Several options for the spectrograph are discussed, building in part on published design studies for E-ELT spectrographs. Indeed...

Foregrounds in Wide-Field Redshifted 21 cm Power Spectra

Thyagarajan, Nithyanandan; Jacobs, Daniel C.; Bowman, Judd D.; Barry, N.; Beardsley, A. P.; Bernardi, G.; Briggs, F.; Cappallo, R. J.; Carroll, P.; Corey, B. E.; de Oliveira-Costa, A.; Dillon, Joshua S.; Emrich, D.; Ewall-Wice, A.; Feng, L.; Goeke, R.; Gr
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
46.892583%
Detection of 21~cm emission of HI from the epoch of reionization, at redshifts z>6, is limited primarily by foreground emission. We investigate the signatures of wide-field measurements and an all-sky foreground model using the delay spectrum technique that maps the measurements to foreground object locations through signal delays between antenna pairs. We demonstrate interferometric measurements are inherently sensitive to all scales, including the largest angular scales, owing to the nature of wide-field measurements. These wide-field effects are generic to all observations but antenna shapes impact their amplitudes substantially. A dish-shaped antenna yields the most desirable features from a foreground contamination viewpoint, relative to a dipole or a phased array. Comparing data from recent Murchison Widefield Array observations, we demonstrate that the foreground signatures that have the largest impact on the HI signal arise from power received far away from the primary field of view. We identify diffuse emission near the horizon as a significant contributing factor, even on wide antenna spacings that usually represent structures on small scales. For signals entering through the primary field of view, compact emission dominates the foreground contamination. These two mechanisms imprint a characteristic "pitchfork" signature on the "foreground wedge" in Fourier delay space. Based on these results...

Interferometric Imaging with the 32 Element Murchison Wide-Field Array

Ord, S. M.; Bowman, J. D.
Fonte: Astronomical Society of the Pacific Publicador: Astronomical Society of the Pacific
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em /11/2010 Português
Relevância na Pesquisa
46.86575%
The Murchison Wide-Field Array (MWA) is a low-frequency radio telescope, currently under construction, intended to search for the spectral signature of the epoch of reionization (EOR) and to probe the structure of the solar corona. Sited in western Australia, the full MWA will comprise 8192 dipoles grouped into 512 tiles and will be capable of imaging the sky south of 40° declination, from 80 MHz to 300 MHz with an instantaneous field of view that is tens of degrees wide and a resolution of a few arcminutes. A 32 station prototype of the MWA has been recently commissioned and a set of observations has been taken that exercise the whole acquisition and processing pipeline. We present Stokes I, Q, and U images from two ~4 hr integrations of a field 20° wide centered on Pictoris A. These images demonstrate the capacity and stability of a real-time calibration and imaging technique employing the weighted addition of warped snapshots to counter extreme wide-field imaging distortions.