Showing papers by "Edward L. Wright published in 2009"

Five-year wilkinson microwave anisotropy probe observations: cosmological interpretation

Abstract: The Wilkinson Microwave Anisotropy Probe (WMAP) 5-year data provide stringent limits on deviations from the minimal, six-parameter Λ cold dark matter model. We report these limits and use them to constrain the physics of cosmic inflation via Gaussianity, adiabaticity, the power spectrum of primordial fluctuations, gravitational waves, and spatial curvature. We also constrain models of dark energy via its equation of state, parity-violating interaction, and neutrino properties, such as mass and the number of species. We detect no convincing deviations from the minimal model. The six parameters and the corresponding 68% uncertainties, derived from the WMAP data combined with the distance measurements from the Type Ia supernovae (SN) and the Baryon Acoustic Oscillations (BAO) in the distribution of galaxies, are: Ω b h 2 = 0.02267+0.00058 –0.00059, Ω c h 2 = 0.1131 ± 0.0034, ΩΛ = 0.726 ± 0.015, ns = 0.960 ± 0.013, τ = 0.084 ± 0.016, and at k = 0.002 Mpc-1. From these, we derive σ8 = 0.812 ± 0.026, H 0 = 70.5 ± 1.3 km s-1 Mpc–1, Ω b = 0.0456 ± 0.0015, Ω c = 0.228 ± 0.013, Ω m h 2 = 0.1358+0.0037 –0.0036, z reion = 10.9 ± 1.4, and t 0 = 13.72 ± 0.12 Gyr. With the WMAP data combined with BAO and SN, we find the limit on the tensor-to-scalar ratio of r 1 is disfavored even when gravitational waves are included, which constrains the models of inflation that can produce significant gravitational waves, such as chaotic or power-law inflation models, or a blue spectrum, such as hybrid inflation models. We obtain tight, simultaneous limits on the (constant) equation of state of dark energy and the spatial curvature of the universe: –0.14 < 1 + w < 0.12(95%CL) and –0.0179 < Ω k < 0.0081(95%CL). We provide a set of WMAP distance priors, to test a variety of dark energy models with spatial curvature. We test a time-dependent w with a present value constrained as –0.33 < 1 + w 0 < 0.21 (95% CL). Temperature and dark matter fluctuations are found to obey the adiabatic relation to within 8.9% and 2.1% for the axion-type and curvaton-type dark matter, respectively. The power spectra of TB and EB correlations constrain a parity-violating interaction, which rotates the polarization angle and converts E to B. The polarization angle could not be rotated more than –59 < Δα < 24 (95% CL) between the decoupling and the present epoch. We find the limit on the total mass of massive neutrinos of ∑m ν < 0.67 eV(95%CL), which is free from the uncertainty in the normalization of the large-scale structure data. The number of relativistic degrees of freedom (dof), expressed in units of the effective number of neutrino species, is constrained as N eff = 4.4 ± 1.5 (68%), consistent with the standard value of 3.04. Finally, quantitative limits on physically-motivated primordial non-Gaussianity parameters are –9 < f local NL < 111 (95% CL) and –151 < f equil NL < 253 (95% CL) for the local and equilateral models, respectively.

Five-Year Wilkinson Microwave Anisotropy Probe Observations: Data Processing, Sky Maps, and Basic Results

Abstract: The Wilkinson Microwave Anisotropy Probe (WMAP) is a Medium-Class Explorer (MIDEX) satellite aimed at elucidating cosmology through full-sky observations of the cosmic microwave background (CMB). The WMAP full-sky maps of the temperature and polarization anisotropy in five frequency bands provide our most accurate view to date of conditions in the early universe. The multi-frequency data facilitate the separation of the CMB signal from foreground emission arising both from our Galaxy and from extragalactic sources. The CMB angular power spectrum derived from these maps exhibits a highly coherent acoustic peak structure which makes it possible to extract a wealth of information about the composition and history of the universe. as well as the processes that seeded the fluctuations. WMAP data have played a key role in establishing ACDM as the new standard model of cosmology (Bennett et al. 2003: Spergel et al. 2003; Hinshaw et al. 2007: Spergel et al. 2007): a flat universe dominated by dark energy, supplemented by dark matter and atoms with density fluctuations seeded by a Gaussian, adiabatic, nearly scale invariant process. The basic properties of this universe are determined by five numbers: the density of matter, the density of atoms. the age of the universe (or equivalently, the Hubble constant today), the amplitude of the initial fluctuations, and their scale dependence. By accurately measuring the first few peaks in the angular power spectrum, WMAP data have enabled the following accomplishments: Showing the dark matter must be non-baryonic and interact only weakly with atoms and radiation. The WMAP measurement of the dark matter density puts important constraints on supersymmetric dark matter models and on the properties of other dark matter candidates. With five years of data and a better determination of our beam response, this measurement has been significantly improved. Precise determination of the density of atoms in the universe. The agreement between the atomic density derived from WMAP and the density inferred from the deuterium abundance is an important test of the standard big bang model. Determination of the acoustic scale at redshift z = 1090. Similarly, the recent measurement of baryon acoustic oscillations (BAO) in the galaxy power spectrum (Eisenstein et al. 2005) has determined the acoustic scale at redshift z approx. 0.35. When combined, these standard rulers accurately measure the geometry of the universe and the properties of the dark energy. These data require a nearly flat universe dominated by dark energy consistent with a cosmological constant. Precise determination of the Hubble Constant, in conjunction with BAO observations. Even when allowing curvature (Omega(sub 0) does not equal 1) and a free dark energy equation of state (w does not equal -1), the acoustic data determine the Hubble constant to within 3%. The measured value is in excellent agreement with independent results from the Hubble Key Project (Freedman et al. 2001), providing yet another important consistency test for the standard model. Significant constraint of the basic properties of the primordial fluctuations. The anti-correlation seen in the temperature/polarization (TE) correlation spectrum on 4deg scales implies that the fluctuations are primarily adiabatic and rule out defect models and isocurvature models as the primary source of fluctuations (Peiris et al. 2003).

Five-year wilkinson microwave anisotropy probe * observations: likelihoods and parameters from the wmap data

Abstract: The Wilkinson Microwave Anisotropy Probe (WMAP), launched in 2001, has mapped out the Cosmic Microwave Background with unprecedented accuracy over the whole sky. Its observations have led to the establishment of a simple concordance cosmological model for the contents and evolution of the universe, consistent with virtually all other astronomical measurements. The WMAP first-year and three-year data have allowed us to place strong constraints on the parameters describing the ACDM model. a flat universe filled with baryons, cold dark matter, neutrinos. and a cosmological constant. with initial fluctuations described by nearly scale-invariant power law fluctuations, as well as placing limits on extensions to this simple model (Spergel et al. 2003. 2007). With all-sky measurements of the polarization anisotropy (Kogut et al. 2003; Page et al. 2007), two orders of magnitude smaller than the intensity fluctuations. WMAP has not only given us an additional picture of the universe as it transitioned from ionized to neutral at redshift z approx.1100. but also an observation of the later reionization of the universe by the first stars. In this paper we present cosmological constraints from WMAP alone. for both the ACDM model and a set of possible extensions. We also consider tlle consistency of WMAP constraints with other recent astronomical observations. This is one of seven five-year WMAP papers. Hinshaw et al. (2008) describe the data processing and basic results. Hill et al. (2008) present new beam models arid window functions, Gold et al. (2008) describe the emission from Galactic foregrounds, and Wright et al. (2008) the emission from extra-Galactic point sources. The angular power spectra are described in Nolta et al. (2008), and Komatsu et al. (2008) present and interpret cosmological constraints based on combining WMAP with other data. WMAP observations are used to produce full-sky maps of the CMB in five frequency bands centered at 23, 33, 41, 61, and 94 GHz (Hinshaw et al. 2008). With five years of data, we are now able to place better limits on the ACDM model. as well as to move beyond it to test the composition of the universe. details of reionization. sub-dominant components, characteristics of inflation, and primordial fluctuations. We have more than doubled the amount of polarized data used for cosmological analysis. allowing a better measure of the large-scale E-mode signal (Nolta et al. 2008). To this end we describe an alternative way to remove Galactic foregrounds from low resolution polarization maps in which Galactic emission is marginalized over, providing a cross-check of our results. With longer integration we also better probe the second and third acoustic peaks in the temperature angular power spectrum, and have many more year-to-year difference maps available for cross-checking systematic effects (Hinshaw et al. 2008).

Five-year wilkinson microwave anisotropy probe observations: angular power spectra

Abstract: We present the temperature and polarization angular power spectra of the cosmic microwave background derived from the first five years of Wilkinson Microwave Anisotropy Probe data. The five-year temperature spectrum is cosmic variance limited up to multipole l = 530, and individual l-modes have signal-to-noise ratio S/N >1 for l < 920. The best-fitting six-parameter ΛCDM model has a reduced χ2 for l = 33-1000 of χ2/ν = 1.06, with a probability to exceed of 9.3%. There is now significantly improved data near the third peak which leads to improved cosmological constraints. The temperature-polarization correlation is seen with high significance. After accounting for foreground emission, the low-l reionization feature in the EE power spectrum is preferred by Δχ2 = 19.6 for optical depth τ = 0.089 by the EE data alone, and is now largely cosmic variance limited for l = 2-6. There is no evidence for cosmic signal in the BB, TB, or EB spectra after accounting for foreground emission. We find that, when averaged over l = 2-6, l(l + 1)C BB l/(2π) < 0.15 μK2 (95% CL).

The Spitzer Deep, Wide-field Survey

Abstract: The Spitzer Deep, Wide-Field Survey (SDWFS) is a four-epoch infrared survey of 10 deg^(2) in the Bootes field of the NOAO Deep Wide-Field Survey using the IRAC instrument on the Spitzer Space Telescope. SDWFS, a Spitzer Cycle 4 Legacy project, occupies a unique position in the area-depth survey space defined by other Spitzer surveys. The four epochs that make up SDWFS permit-for the first time-the selection of infrared-variable and high proper motion objects over a wide field on timescales of years. Because of its large survey volume, SDWFS is sensitive to galaxies out to z ~ 3 with relatively little impact from cosmic variance for all but the richest systems. The SDWFS data sets will thus be especially useful for characterizing galaxy evolution beyond z ~ 1.5. This paper explains the SDWFS observing strategy and data processing, presents the SDWFS mosaics and source catalogs, and discusses some early scientific findings. The publicly released, full-depth catalogs contain 6.78, 5.23, 1.20, and 0.96 x 10^(5) distinct sources detected to the average 5 sigma, 4"-diameter, aperture-corrected limits of 19.77, 18.83, 16.50, and 15.82 Vega mag at 3.6, 4.5, 5.8, and 8.0 mu m, respectively. The SDWFS number counts and color-color distribution are consistent with other, earlier Spitzer surveys. At the 6 minute integration time of the SDWFS IRAC imaging, > 50% of isolated Faint Images of the Radio Sky at Twenty cm radio sources and > 80% of on-axis XBootes sources are detected out to 8.0 mu m. Finally, we present the four highest proper motion IRAC-selected sources identified from the multi-epoch imaging, two of which are likely field brown dwarfs of mid-T spectral class.

Five-year wilkinson microwave anisotropy probe * observations: galactic foreground emission

Abstract: We present a new estimate of foreground emission in the Wilkinson Microwave Anisotropy Probe (WMAP) data, using a Markov chain Monte Carlo method. The new technique delivers maps of each foreground component for a variety of foreground models with estimates of the uncertainty of each foreground component, and it provides an overall goodness-of-fit estimate. The resulting foreground maps are in broad agreement with those from previous techniques used both within the collaboration and by other authors. We find that for WMAP data, a simple model with power-law synchrotron, free-free, and thermal dust components fits 90% of the sky with a reduced χ2 ν of 1.14. However, the model does not work well inside the Galactic plane. The addition of either synchrotron steepening or a modified spinning dust model improves the fit. This component may account for up to 14% of the total flux at the Ka band (33 GHz). We find no evidence for foreground contamination of the cosmic microwave background temperature map in the 85% of the sky used for cosmological analysis.

Five-Year Wilkinson Microwave Anisotropy Probe (WMAP) Observations: Bayesian Estimation of Cosmic Microwave Background Polarization Maps

Abstract: We describe a sampling method to estimate the polarized cosmic microwave background (CMB) signal from observed maps of the sky. We use a Metropolis-within-Gibbs algorithm to estimate the polarized CMB map, containing Q and U Stokes parameters at each pixel, and its covariance matrix. These can be used as inputs for cosmological analyses. The polarized sky signal is parameterized as the sum of three components: CMB, synchrotron emission, and thermal dust emission. The polarized Galactic components are modeled with spatially varying power-law spectral indices for the synchrotron, and a fixed power law for the dust, and their component maps are estimated as by-products. We apply the method to simulated low-resolution maps with pixels of side 7.2 deg, using diagonal and full noise realizations drawn from the WMAP noise matrices. The CMB maps are recovered with goodness of fit consistent with errors. Computing the likelihood of the E-mode power in the maps as a function of optical depth to reionization, {tau}, for fixed temperature anisotropy power, we recover {tau} = 0.091 {+-} 0.019 for a simulation with input {tau} = 0.1, and mean {tau} = 0.098 averaged over 10 simulations. A 'null' simulation with no polarized CMB signal has maximum likelihoodmore » consistent with {tau} = 0. The method is applied to the five-year WMAP data, using the K, Ka, Q, and V channels. We find {tau} = 0.090 {+-} 0.019, compared to {tau} = 0.086 {+-} 0.016 from the template-cleaned maps used in the primary WMAP analysis. The synchrotron spectral index, {beta}, averaged over high signal-to-noise pixels with standard deviation {sigma}({beta}) < 0.25, but excluding {approx}6% of the sky masked in the Galactic plane, is -3.03 {+-} 0.04. This estimate does not vary significantly with Galactic latitude, although includes an informative prior.« less

Five-year wilkinson microwave anisotropy probe observations: source catalog

Abstract: We present the list of point sources found in the Wilkinson Microwave Anisotropy Probe (WMAP) five-year maps. The technique used in the first-year and three-year analyses now finds 390 point sources, and the five-year source catalog is complete for regions of the sky away from the Galactic plane to a 2 Jy limit, with SNR >4.7 in all bands in the least covered parts of the sky. The noise at high frequencies is still mainly radiometer noise, but at low frequencies the cosmic microwave background (CMB) anisotropy is the largest uncertainty. A separate search of CMB-free V-W maps finds 99 sources of which all but one can be identified with known radio sources. The sources seen by WMAP are not strongly polarized. Many of the WMAP sources show significant variability from year to year, with more than a 2:1 range between the minimum and maximum fluxes.

Five-year wilkinson microwave anisotropy probe ∗ observations: beam maps and window functions

Abstract: Cosmology and other scientific results from the WMAP mission require an accurate knowledge of the beam patterns in flight. While the degree of beam knowledge for the WMAP one-year and three-year results was unprecedented for a CMB experiment, we have significantly improved the beam determination as part of the five-year data release. Physical optics fits are done on both the A and the B sides for the first time. The cutoff scale of the fitted distortions on the primary mirror is reduced by a factor of approximately 2 from previous analyses. These changes enable an improvement in the hybridization of Jupiter data with beam models, which is optimized with respect to error in the main beam solid angle. An increase in main-beam solid angle of approximately 1% is found for the V2 and W1-W4 differencing assemblies. Although the five-year results are statistically consistent with previous ones, the errors in the five-year beam transfer functions are reduced by a factor of approximately 2 as compared to the three-year analysis. We present radiometry of the planet Jupiter as a test of the beam consistency and as a calibration standard; for an individual differencing assembly. errors in the measured disk temperature are approximately 0.5%.

SPACE: the spectroscopic all-sky cosmic explorer

Abstract: We describe the scientific motivations, the mission concept and the instrumentation of SPACE, a class-M mission proposed for concept study at the first call of the ESA Cosmic-Vision 2015–2025 planning cycle. SPACE aims to produce the largest three-dimensional evolutionary map of the Universe over the past 10 billion years by taking near-IR spectra and measuring redshifts for more than half a billion galaxies at 0 < z < 2 down to AB~23 over 3π sr of the sky. In addition, SPACE will also target a smaller sky field, performing a deep spectroscopic survey of millions of galaxies to AB~26 and at 2 < z < 10 +. These goals are unreachable with ground-based observations due to the ≈500 times higher sky background (see e.g. Aldering, LBNL report number LBNL-51157, 2001). To achieve the main science objectives, SPACE will use a 1.5 m diameter Ritchey-Chretien telescope equipped with a set of arrays of Digital Micro-mirror Devices covering a total field of view of 0.4 deg2, and will perform large-multiplexing multi-object spectroscopy (e.g. ≈6000 targets per pointing) at a spectral resolution of R~400 as well as diffraction-limited imaging with continuous coverage from 0.8 to 1.8 μm. Owing to the depth, redshift range, volume coverage and quality of its spectra, SPACE will reveal with unique sensitivity most of the fundamental cosmological signatures, including the power spectrum of density fluctuations and its turnover. SPACE will also place high accuracy constraints on the dark energy equation of state parameter and its evolution by measuring the baryonic acoustic oscillations imprinted when matter and radiation decoupled, the distance-luminosity relation of cosmological supernovae, the evolution of the cosmic expansion rate, the growth rate of cosmic large-scale structure, and high-z galaxy clusters. The datasets from the SPACE mission will represent a long lasting legacy for the whole astronomical community whose data will be mined for many years to come.

Design of a G-band sheet-beam Extended-Interaction Klystron

Abstract: The preliminary design of a four-cavity G-band sheet-beam Extended-Interaction Klystron (EIK) Circuit is presented. The circuit design has been performed with the self-consistent particle-in-cell (PIC) code MAGIC-3D. All cavities operate in the 2-π mode. The circuit is powered by a 520 mA, 16.5 kV sheet-electron beam. Output power of 453 W is achieved with an input power of 25 mW, corresponding to an electronic gain of 41.6 dB in a circuit length of approximately of 1.2 cm.

Extragalactic Point Source Search in Five-Year WMAP 41, 61, and 94 Ghz Maps

Abstract: We present the results of an extragalactic point source search using the five-year Wilkinson Microwave Anisotropy Probe (WMAP) 41, 61, and 94 GHz (Q, V, and W bands) temperature maps. This work is an extension of our designing and applying a cosmic microwave background (CMB)-free technique to extract point sources in the WMAP maps. Specifically, we have formed an internal linear combination map of the three-band maps, with the weights chosen to remove the CMB anisotropy signal as well as to favor the selection of flat-spectrum sources. We have also constructed a filter to recover the true point source flux distribution on the sky. A total of 381 sources are found in our study at the >5σ level outside the WMAP point source detection mask, among which 89 are new (i.e., not present in the WMAP catalogs). Source fluxes have been calculated and corrected for the Eddington bias. We have solidly identified 367 (96.3%) of our sources, the 1σ positional uncertainty of which is 2'. The 14 unidentified sources could be either extended radio structure or obscured by Galactic emission. We have also applied the same detection approach to simulated maps, which yielded 364 ± 21 detections on average. The recovered source distribution N(>S) agrees well with the simulation input, which proves the reliability of this method.

Experimental Study and Analysis of an S-Band Multiple-Beam Klystron With 6% Bandwidth

Abstract: We present experimental results and analyses of an eight-beam five-cavity multiple-beam klystron (MBK) operating at a center frequency of ~3.2 GHz. The device met its performance goals in its first hardware implementation, generating a peak RF output power of 600 kW and a 3-dB bandwidth of ~6%. The circuit was modeled with TESLA, a 2.5-D large-signal klystron/MBK code that was extended to enable simulations of the low- Q multiple-gap cavities used to increase the bandwidth. Details of the model and underlying theory are described, and the simulation results are compared with experimental measurements. The good agreement between the model and the experiment provides a validation for our tools and techniques that will be used in the design of future devices.

Broadband High-Power 18-Beam S-Band Klystron Amplifier Design

Abstract: Fundamental-mode multiple-beam klystrons (MBKs) offer the potential of high power and broad bandwidth with low noise at low beam voltages in a compact amplifier form factor. This paper presents the design approach and methodology for an S-band MBK. This amplifier will be driven by a newly developed 41.6-A 42-kV 18-beam electron gun. The high total beam perveance permits the circuit design to achieve a peak power of 670 kW in S-band and a corresponding 1-dB bandwidth of 13% (16% at 3-dB). The high beam perveance, however, requires special considerations in the common collector design, particularly with respect to the spent modulated electron beams. To fully account for the impact of the time-varying beam current, the time-dependent 3-D gun/collector code MICHELLE was employed for this collector design.

A New Era in Extragalactic Background Light Measurements: The Cosmic History of Accretion, Nucleosynthesis and Reionization

Abstract: (Brief Summary) What is the total radiative content of the Universe since the epoch of recombination? The extragalactic background light (EBL) spectrum captures the redshifted energy released from the first stellar objects, protogalaxies, and galaxies throughout cosmic history. Yet, we have not determined the brightness of the extragalactic sky from UV/optical to far-infrared wavelengths with sufficient accuracy to establish the radiative content of the Universe to better than an order of magnitude. Among many science topics, an accurate measurement of the EBL spectrum from optical to far-IR wavelengths, will address: What is the total energy released by stellar nucleosynthesis over cosmic history? Was significant energy released by non-stellar processes? Is there a diffuse component to the EBL anywhere from optical to sub-millimeter? When did first stars appear and how luminous was the reionization epoch? Absolute optical to mid-IR EBL spectrum to an astrophysically interesting accuracy can be established by wide field imagingat a distance of 5 AU or above the ecliptic plane where the zodiacal foreground is reduced by more than two orders of magnitude.

The Spitzer Deep, Wide-Field Survey

Abstract: The Spitzer Deep, Wide-Field Survey (SDWFS) is a four-epoch infrared survey of ten square degrees in the Bootes field of the NOAO Deep Wide-Field Survey using the IRAC instrument on the Spitzer Space Telescope. SDWFS, a Cycle four Spitzer Legacy project, occupies a unique position in the area-depth survey space defined by other Spitzer surveys. The four epochs that make up SDWFS permit -- for the first time -- the selection of infrared-variable and high proper motion objects over a wide field on timescales of years. Because of its large survey volume, SDWFS is sensitive to galaxies out to z~3 with relatively little impact from cosmic variance for all but the richest systems. The SDWFS datasets will thus be especially useful for characterizing galaxy evolution beyond z~1.5. This paper explains the SDWFS observing strategy and data processing, presents the SDWFS mosaics and source catalogs, and discusses some early scientific findings. The publicly-released, full-depth catalogs contain 6.78, 5.23, 1.20, and 0.96 x 10e5 distinct sources detected to the average 5-sigma, 4" diameter, aperture-corrected limits of 19.77, 18.83, 16.50, and 15.82 Vega mag at 3.6, 4.5, 5.8, and 8.0 micron, respectively. The SDWFS number counts and color-color distribution are consistent with other, earlier Spitzer surveys. At the 6 min integration time of the SDWFS IRAC imaging, more than 50% of isolated FIRST radio sources and more than 80% of on-axis XBootes sources are detected out to 8.0 micron. Finally, we present the four highest proper motion IRAC-selected sources identified from the multi-epoch imaging, two of which are likely field brown dwarfs of mid-T spectral class.

A New Era in Extragalactic Background Light Measurements: The Cosmic History of Accretion, Nucleosynthesis and Reionization

Abstract: Asantha Cooray Alexandre Amblard, Charles Beichman, Dominic Benford, Rebecca Bernstein, James J. Bock, Mark Brodwin, Volker Bromm, Renyue Cen, Ranga R. Chary, Mark Devlin, Timothy Dolch, Herve Dole, Eli Dwek, David Elbaz, Michael Fall, Giovanni Fazio, Henry Ferguson, Steven Furlanetto, Jonathan Gardner, Mauro Giavalisco, Rudy Gilmore, Nickolay Gnedin, Anthony Gonzalez, Zoltan Haiman, Michael Hauser, Jiasheng Huang, Sergei Ipatov, Alexander Kashlinsky, Brian Keating, Thomas Kelsall, Eiichiro Komatsu, Guilaine Lagache, Louis R. Levenson, Avi Loeb, Piero Madau, John C. Mather, Toshio Matsumoto, Shuji Matsuura, Kalevi Mattila, Harvey Moseley, Leonidas Moustakas, S. Peng Oh, Larry Petro, Joel Primack, William Reach, Tom Renbarger, Paul Shapiro, Daniel Stern, Ian Sullivan, Aparna Venkatesan, Michael Werner, Rogier Windhorst, Edward L. Wright, Michael Zemcov

Photometric Calibrations for 21st Century Science

Abstract: The answers to fundamental science questions in astrophysics, ranging from the history of the expansion of the universe to the sizes of nearby stars, hinge on our ability to make precise measurements of diverse astronomical objects. As our knowledge of the underlying physics of objects improves along with advances in detectors and instrumentation, the limits on our capability to extract science from measurements is set, not by our lack of understanding of the nature of these objects, but rather by the most mundane of all issues: the precision with which we can calibrate observations in physical units. We stress the need for a program to improve upon and expand the current networks of spectrophotometrically calibrated stars to provide precise calibration with an accuracy of equal to and better than 1% in the ultraviolet, visible and near-infrared portions of the spectrum, with excellent sky coverage and large dynamic range.

Multiple-beam klystron development at the Naval Research Laboratory

Abstract: Multiple-beam klystrons (MBKs) are a vacuum electronic amplifier technology that can provide the high power, low-noise, broadband, compact transmitter technology required to meet the needs of modern surveillance radar systems. We present a review of MBK development at the Naval Research Laboratory and the creation of an accurate, simulation-based MBK design methodology. Examples of specific devices include S-band amplifiers generating up to 670 kW peak power with bandwidths up to 13%. We also present examples of potential radar system applications using MBKs.

A Vigorous Explorer Program

Abstract: Explorers have made breakthroughs in many fields of astrophysics. The science from both these missions contributed to three Nobel Prizes - Giacconi (2002), Mather, and Smoot (2006). Explorers have: marked the definitive beginning of precision cosmology, discovered that short gamma-ray bursts are caused by compact star mergers and have measured metalicity to redshifts z>6. NASA Explorers do cutting-edge science that cannot be done by facility-class instruments. The Explorer program provides a rapid response to changing science and technology, to enable cutting-edge science at moderate cost. Explorers also enable innovation, and engage & train scientists, managers and engineers, adding human capital to NASA and the nation. The astrophysics Explorer launch rate now being achieved is 1 per 3 years, and budget projections are in the $150M/year range for the next five years. A newly Vigorous Explorer Program should be created to: 1. Reach the long-stated goal of annual astrophysics launches; 2. Find additional launch options for Explorers and actively encourage cost savings in launchers and spacecraft, such as new commercial vehicles and innovative partnerships. 3. Mitigate risk via stronger technical development and sub-orbital programs, and through longer, more thorough, Phase A programs, potentially reducing the need for a 30% contingency; 4. Strive to protect the funding for missions that have reached Phase B, to prevent significant launch slips and cancellations, with a goal of 4 to 5 years from Phase B to launch; 5. Review the project management procedures and requirements to seek cost reductions, including the risk management strategy and the review and reporting process; 6. Review and possibly modify the cost caps for all Explorer classes to optimize scientific returns per dollar. [ABRIDGED]

Modeling and design of high-power single-beam and multiple-beam Inductive Output Tubes

Abstract: The Inductive Output Tube (IOT) is today the device-of-choice for terrestrial UHF broadcast applications due to the IOT's high efficiency with linearity and compact size. The accelerator community is also making the transition to IOT technology for a number of high-power UHF and L-band applications as a result of these benefits. Although the IOT appears to be quite simple, the actual operation of the device is quite complex and difficult to analyze quantitatively. Consequently, we are investigating the physics of the beam-wave interaction of the IOT with the goal of achieving significantly higher power operation. The time-domain electrostatic PIC code MICHELLE, in conjunction with the Analyst® suite of electromagnetic codes, were used to model the cathode-grid-anode structure that comprise the input cavity. Our investigation has led to the discovery of a mechanism responsible for intra-bunch charge formation. Time-domain PIC results of this effect will be shown. We will also present simulation results of the large-signal beam wave interaction in the output cavity using the code TESLA. Examples of single beam and multiple-beam (MB) IOT designs will also be shown.

Experimental progress on the development of a multiple-beam klystron with 13% bandwidth

Abstract: We present recent progress on the development of a multiple-beam klystron (MBK) designed to operate in S-band with a 1-dB bandwidth of 13%. The amplifier is powered by an 18-beam electron gun operating at a voltage of 42 kV and a total current of 41.6 A. Measured gun voltage-current characteristics will be compared with the design predictions made by the 3D particle code, MICHELLE. Experimental measurements of the frequency and Q's of individual cavities comprising the interaction circuit will be compared with 3D electromagnetic simulations. Finally, as available, we will also report on hot test measurements of the rf performance of the MBK.

WISE- the Wide-field Infrared Survey Explorer

Abstract: The Wide-field Infrared Survey Explorer (WISE) is a medium class NASA Explorer mission designed to map the entire sky in 4 mid-infrared bands, with band centers at 3.4, 4.6, 12 & 22 μm. The sensitivity requirements are 120, 160, 850 & 4000 μJy in these bands. The angular resolution should be 6" FWHMor better except at 22 μm where diffraction in the 40 cm diameter aperture degrades the resolution to 12" FWHM. WISE takes images simultaneously in all 4 bands in a 47' FOV using 1024 2 pixel arrays and 2.75" pixels. WISE will be launched into a 500 km altitude 97° inclination Sun-synchronous orbit at the terminator. Launch is currently scheduled for 6 AM in late 2009. WISE scans a circle perpendicular to the Earth-Sun line which leads to an all-sky survey in 6 months.

Space-Based Research in Fundamental Physics and Quantum Technologies

Abstract: Space offers unique experimental conditions and a wide range of opportunities to explore the foundations of modern physics with an accuracy far beyond that of ground-based experiments. Space-based experiments today can uniquely address important questions related to the fundamental laws of Nature. In particular, high-accuracy physics experiments in space can test relativistic gravity and probe the physics beyond the Standard Model; they can perform direct detection of gravitational waves and are naturally suited for investigations in precision cosmology and astroparticle physics. In addition, atomic physics has recently shown substantial progress in the development of optical clocks and atom interferometers. If placed in space, these instruments could turn into powerful high-resolution quantum sensors greatly benefiting fundamental physics. We discuss the current status of space-based research in fundamental physics, its discovery potential, and its importance for modern science. We offer a set of recommendations to be considered by the upcoming National Academy of Sciences' Decadal Survey in Astronomy and Astrophysics. In our opinion, the Decadal Survey should include space-based research in fundamental physics as one of its focus areas. We recommend establishing an Astronomy and Astrophysics Advisory Committee's interagency "Fundamental Physics Task Force" to assess the status of both ground- and space-based efforts in the field, to identify the most important objectives, and to suggest the best ways to organize the work of several federal agencies involved. We also recommend establishing a new NASA-led interagency program in fundamental physics that will consolidate new technologies, prepare key instruments for future space missions, and build a strong scientific and engineering community. Our goal is to expand NASA's science objectives in space by including "laboratory research in fundamental physics" as an element in the agency's ongoing space research efforts.

Characterizing Extrasolar Planetary Systems

Abstract: The quest to detect and characterize exoplanets, and learn how they form is one of the most exciting science challenges of this century, one that opens new horizons in human knowledge. To meet this challenge new approaches are needed both observationally and theoretically. This paper summarizes powerful new measurement techniques that will aid in this quest. In particular, we describe how dust structures in debris disks will reveal otherwise undetectable planets, how the atmospheres of non-transiting extrasolar gas and ice giant planets can be probed spectroscopically, how observations can be used to measure the gas dissipation timescale in protoplanetary disks, and how it will be possible to understand the mechanism that delivered water to the Earth’s surface. Sensitive, high angular resolution measurements in the mid-IR to submillimeter spectral range will be needed to exploit these promising techniques. Section 1 of this paper describes four new measurement techniques, each of which has the potential to improve vastly our understanding of exoplanets and the planet formation process. Section 2 summarizes the measurement capabilities needed to implement these techniques. 1.1 Image irregular structures in dusty debris disks to find and characterize exoplanets The locations, masses and orbits of unseen planets can be deduced from the shapes of structures in dusty debris disks and from temporal variations in these structures, just as new Saturnian moons were found after ring gaps and features divulged their hiding places. The orbits of dust grains in developing and established planetary systems (i.e., debris disks) are perturbed gravitationally by any planets that may be present. Orbital resonances with the planets shepherd the dust into clumpy circumstellar ring structures, which have been observed at visible to millimeter wavelengths. These circumstellar structures can be decoded to reveal a planet's mass and orbital parameters, as well as the dominant dust grain size in the disk. Planet-hunting methods reliant upon measurements of the radial or proper motion of a planet’s parent star, or on transits of the star, have been very successful, but these methods all favor the detection of planets in close orbits. A key virtue of the debris disk imagery method is its ability to reveal planets in distant orbits, and thereby enable a more complete census of extrasolar planetary systems. Our understanding of planet formation depends on the availability of such a census. a NASA GSFC; b Caltech; c NASA Postdoctoral Fellow; d Jet Propulsion Laboratory; e U Maryland; f NOAO; g Johns Hopkins U; h IPAC; i UCLA Interplanetary dust at orbital distances likely occupied by planets glows most brightly in the far-infrared spectral range ~20 – 60 μm. Main sequence stars are faint at these wavelengths, so the starlight needn’t be blocked to allow disk imaging. The Spitzer Space Telescope demonstrated the power of far-IR debris disk imagery. Spitzer resolved the nearest four debris disks, at distances of only a few parsecs (Figure 1a), but an important objective is to understand our own solar system in the context of a representative statistical sample of exoplanetary systems. By imaging the disks around stars of many spectral types we will learn how planet formation depends on stellar mass. To achieve this objective, it will be necessary to detect 1 AU structures in debris disks out to a distance of ~10 pc, implying an angular resolution requirement of 0.1 arcsec. ALMA will be well-suited spatially, but its measurements will be far into the Rayleigh-Jeans regime, where the thermal emission from interplanetary dust is relatively faint. JWST will probe debris disks at wavelengths close to the emission peak, but with only 1 arcsecond angular resolution. What is needed instead is a capability for 0.1 arcsecond images in the midto far-IR (Figure 1b). Figure 1 –Spitzer resolves four nearby debris disks, including Fomalhaut, shown here (a) at 24 and 70 μm. A far-IR observatory with angular resolution a hundred-fold better than that of Spitzer could provide clear images of a large statistical sample of debris disks, enabling discoveries of new planets and a great improvement in our understanding of the factors that influence the evolution of planetary systems. The model images in (b), based on Eps Eri but scaled to 30 pc, show the predicted far-IR emission at 40, 60, and 100 μm color-coded as blue, green, and red, respectively. The dust-trapping planet (+) is shown at two orbital phases, and the resonantly trapped dust grains can be seen to have moved. 1.2 Characterize gas and ice giant exoplanets to constrain models of planetary system formation To understand planet migration and gain insight into the planet formation process, it will be imperative to characterize giant exoplanets at all orbital radii. Recent Spitzer observations of transiting extrasolar giant planets demonstrate the value of IR spectroscopy as a tool to constrain a planet’s temperature structure and probe the composition of its atmosphere. Soon JWST observers will be able to use the same technique to probe dimmer planets and fainter spectral features. However, transiting planets tend to be in close orbits and preferentially tell us about “hot Jupiters.” Exoplanets in distant orbits, like the gas and ice giants in our own solar system, have a very low probability of being seen in transit. An alternative technique is needed to characterize such planets. The spectra of non-transiting giant exoplanets could be measured with a Michelson stellar interferometer equipped with a Fourier Transform Spectrometer, a so-called “double Fourier” interferometer. To such an instrument the planet’s light would appear as the modulating signal component when the baseline position angle is varied, while starlight would produce a stable fringe pattern. With sufficient signal-to-noise ratio, the planet’s interferogram could be extracted and Fourier transformed to obtain the desired spectrum, and the planet’s orbital position could be measured. In the far-IR, where the planet-to-star contrast ratio is at a maximum (Figure 2, left), starlight nulling is not necessary and detection is possible if the exoplanet is separated from the star by an angle greater than λ/2B, where λ is the wavelength and B is the length of the interferometric baseline. Taking Jupiter as an example (Figure 2, right), we can expect to detect broad NH3 bands, which dominate the spectrum from 40 to 100 μm, and to study the abundances of key chemical species such as water and methane. The observed spectra of giant planets, when coupled with independent planet mass estimates (e.g., from the debris disk sculpting method described above), will test models for planetary atmospheres and serve as an empirical set of spectral benchmarks. The proposed spectroscopic measurements will be challenging, but not more difficult than the differential measurements (star + planet minus star) required in the transiting technique. A structurally connected infrared interferometer of modest size (~40 m) could probe planets at 0.1 arcsec orbital radii (i.e., 1 AU at 10 pc). Figure 2. Left panel: The atmospheres of giant planets will be seen in highest contrast relative to their parent stars in the far-infrared. Right panel: This spectrum of Jupiter from the Cassini Composite Infrared Spectrometer shows CH4, NH3, and PH3 absorption lines and was used to place chemically interesting limits on the mole fractions of HF, HCl, HBr, and HI in the jovian troposphere. How common are planetary systems like our own? The discovery and characterization of planets in distant orbits around stars with a wide range of masses, ages and heavy element concentrations, will dramatically advance the burgeoning field of comparative planetology and provide stringent new tests of theoretical models for planet formation. 1.3 Observe the transition from protoplanetary to debris disks to learn the effects of gas dissipation on planet formation A white paper by Mundy et al. will discuss observational methods to probe the early phases of star and planetary system formation. Here we discuss the interesting transition phase between a gas-rich proto-planetary disk and an older debris disk from which the gas has vanished. When does gas dissipation occur, and how does this affect the migration of planetary bodies and the outcome of the planet formation process? How does the dissipation process depend on the heavy element composition of the protoplanetary nebula, the mass of the newborn star, and the environment in which star formation takes place? By measuring the gas contents of planet forming disks of various ages it will be possible to constrain the timescale for gas giant planet formation and the migration of planetary bodies of all sizes. Spitzer has already enabled pathfinding studies. The Herschel Space Observatory will observe disks in the far-infrared, measuring numerous lines from hydrides, such as CH and OH, and the strong [C I], [O I] and [C II] fine structure lines at 370, 146, 63 and 158 μm. When coupled with models, far-IR spectral line observations will give us new insight into the chemistry and physical conditions in young planet forming disks. The C/O ratio, derivable from these observations, is thought to affect the composition, surface chemistry, and perhaps the habitability of planets. Following closely behind Herschel, ALMA and JWST will play major roles in studies of gasrich and gas-poor disks. With ALMA we will be able to make spectral line maps in surrogate tracers of total gas density, such as CO and its less abundant isotopes. Unfortunately, total gas density estimates based upon measurements of such proxies can be significantly biased, as CO molecules can be photodissociated or frozen onto grain surfaces. JWST will attack this problem head-on by directly measuring the readily excited 17 and 28 μm rotational lines of H2. JWST will measure the total gas conte

Applications and current status of the finite-element MICHELLE gun & collector simulation code

Abstract: The MICHELLE code is a Finite-Element Electrostatic Particle in Cell code for application to 2D and 3D particle beam formation, transport, and collection. Its primary development focus has been for DC electron guns and depressed collectors, however, it has other applications such as RF electron guns, ion thrusters, photocathodes, etc. Its ability to manage large mesh sizes and large particle counts in complex geometries requiring the resolution of disparate spatial scales in 2D and 3D on desktop computers has allowed it to be applied to devices that could not have been readily modeled in recent years. This presentation gives an overview of recent applications, capabilities, and the current status of MICHELLE. In particular, application to time-dependent problems and optimization will be illustrated