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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 883 records · Page 49
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DOE OSTI2012

USING COSMIC MICROWAVE BACKGROUND LENSING TO CONSTRAIN THE MULTIPLICATIVE BIAS OF COSMIC SHEAR

Weak gravitational lensing is one of the key probes of cosmology. Cosmic shear surveys aimed at measuring the distribution of matter in the universe are currently being carried out (Pan-STARRS) or planned for the coming decade (DES, LSST, EUCLID, WFIRST). Crucial to the success of these surveys is the control of systematics. In this work, a new method to constrain one such family of systematics, known as multiplicative bias, is proposed. This method exploits the cross-correlation between weak-lensing measurements from galaxy surveys and the ones obtained from high-resolution cosmic microwave background experiments. This cross-correlation is shown to have the power to break the degeneracy between the normalization of the matter power spectrum and the multiplicative bias of cosmic shear and to be able to constrain the latter to a few percent.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

MULTIPLE PLASMA EJECTIONS AND INTERMITTENT NATURE OF MAGNETIC RECONNECTION IN SOLAR CHROMOSPHERIC ANEMONE JETS

The recent discovery of chromospheric anemone jets with the Solar Optical Telescope (SOT) on board Hinode has shown an indirect evidence of magnetic reconnection in the solar chromosphere. However, the basic nature of magnetic reconnection in chromosphere is still unclear. We studied nine chromospheric anemone jets from SOT/Hinode using Ca II H filtergrams, and we found multiple bright, plasma ejections along the jets. In most cases, the major intensity enhancements (larger than 30% relative to the background intensity) of the loop correspond to the timing of the plasma ejections. The typical lifetime and size of the plasma ejecta are about 20-60 s and 0.3-1.5 Mm, respectively. The height-time plot of jet shows many sub-structures (or individual jets) and the typical lifetime of the individual jet is about one to five minutes. Before the onset of the jet activity, a loop appears in Ca II H and gradually increases in size, and after few minutes several jets are launched from the loop. Once the jet activity starts and several individual jets are launched, the loop starts shrinking with a speed of {approx}4 km s{sup -1}. In some events, a downward moving blob with a speed of {approx}35 km s{sup -1} was observed, associated with the upward moving plasma along one of the legs of the loop hosting the jets. The upward moving plasma gradually developed into jets. Multiple plasma ejections in chromospheric anemone jet show the strongly time-dependent as well as intermittent nature of magnetic reconnection in the solar chromosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

HUBBLE SPACE TELESCOPE REVEALS MULTIPLE SUB-GIANT BRANCH IN EIGHT GLOBULAR CLUSTERS

In the last few years many globular clusters (GCs) have revealed complex color-magnitude diagrams, with the presence of multiple main sequences (MSs), broad or multiple sub-giant branches (SGBs) and MS turnoffs, and broad or split red giant branches (RGBs). After a careful correction for differential reddening, high-accuracy photometry with the Hubble Space Telescope (HST) presented in this paper reveals a broadened or even split SGB in five additional Milky Way GCs: NGC 362, NGC 5286, NGC 6656, NGC 6715, and NGC 7089. In addition, we confirm (with new and archival HST data) the presence of a split SGB in 47 Tuc, NGC 1851, and NGC 6388. The fraction of faint SGB stars with respect to the entire SGB population varies from one cluster to another and ranges from {approx}0.03 for NGC 362 to {approx}0.50 for NGC 6715. The average magnitude difference between the bright SGB and the faint SGB is almost the same at different wavelengths. This peculiarity is consistent with the presence of two groups of stars with either an age difference of about 1-2 Gyr or a significant difference in their overall C+N+O content.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

DIFFERENTIAL EMISSION MEASURE ANALYSIS OF MULTIPLE STRUCTURAL COMPONENTS OF CORONAL MASS EJECTIONS IN THE INNER CORONA

In this paper, we study the temperature and density properties of multiple structural components of coronal mass ejections (CMEs) using differential emission measure (DEM) analysis. The DEM analysis is based on the six-passband EUV observations of solar corona from the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. The structural components studied include the hot channel in the core region (presumably the magnetic flux rope of the CME), the bright loop-like leading front (LF), and coronal dimming in the wake of the CME. We find that the presumed flux rope has the highest average temperature (>8 MK) and density ({approx}1.0 Multiplication-Sign 10{sup 9} cm{sup -3}), resulting in an enhanced emission measure over a broad temperature range (3 {<=} T(MK) {<=} 20). On the other hand, the CME LF has a relatively cool temperature ({approx}2 MK) and a narrow temperature distribution similar to the pre-eruption coronal temperature (1 {<=} T(MK) {<=} 3). The density in the LF, however, is increased by 2%-32% compared with that of the pre-eruption corona, depending on the event and location. In coronal dimmings, the temperature is more broadly distributed (1 {<=} T(MK) {<=} 4), but the density decreases by {approx}35%-{approx}40%. These observational results show that: (1) CME core regions are significantly heated, presumably through magnetic reconnection; (2) CME LFs are a consequence of compression of ambient plasma caused by the expansion of the CME core region; and (3) the dimmings are largely caused by the plasma rarefaction associated with the eruption.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

STAR FORMATION HISTORIES OF GLOBULAR CLUSTERS WITH MULTIPLE POPULATIONS. I. {omega} CEN, M22, AND NGC 1851

There is increasing evidence that some massive globular clusters (GCs) host multiple stellar populations having different heavy element abundances enriched by supernovae. They usually accompany multiple red giant branches (RGBs) in the color-magnitude diagrams (CMDs), and are distinguished from most of the other GCs which display variations only in light element abundances. In order to investigate the star formation histories of these peculiar GCs, we have constructed synthetic CMDs for {omega} Cen, M22, and NGC 1851. Our models are based on the updated versions of Yonsei-Yale (Y{sup 2}) isochrones and horizontal branch (HB) evolutionary tracks which include the cases of enhancements in both helium and the total CNO abundances. To estimate ages and helium abundances of subpopulations in each GC, we have compared our models with the observations on the Hess diagram by employing a {chi}{sup 2} minimization technique. We find that metal-rich subpopulations in each of these GCs are also enhanced in helium abundance, and the age differences between the metal-rich and metal-poor subpopulations are fairly small ({approx}0.3-1.7 Gyr), even in the models with the observed variations in the total CNO content. These are required to simultaneously reproduce the observed extended HB and the splits on the main sequence, subgiant branch, and RGB. Our results are consistent with the hypothesis that these GCs are the relics of more massive primeval dwarf galaxies that merged and disrupted to form the proto-Galaxy.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

RHESSI AND TRACE OBSERVATIONS OF MULTIPLE FLARE ACTIVITY IN AR 10656 AND ASSOCIATED FILAMENT ERUPTION

We present Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and Transition Region and Coronal Explorer (TRACE) observations of multiple flare activity that occurred in the NOAA active region 10656 over a period of 2 hr on 2004 August 18. Out of four successive flares, three were class C events, and the final event was a major X1.8 solar eruptive flare. The activities during the pre-eruption phase, i.e., before the X1.8 flare, are characterized by three localized episodes of energy release occurring in the vicinity of a filament that produces intense heating along with non-thermal emission. A few minutes before the eruption, the filament undergoes an activation phase during which it slowly rises with a speed of {approx}12 km s{sup -1}. The filament eruption is accompanied by an X1.8 flare, during which multiple hard X-ray (HXR) bursts are observed up to 100-300 keV energies. We observe a bright and elongated coronal structure simultaneously in E(UV) and 50-100 keV HXR images underneath the expanding filament during the period of HXR bursts, which provides strong evidence for ongoing magnetic reconnection. This phase is accompanied by very high plasma temperatures of {approx}31 MK, followed by the detachment of the prominence from the solar source region. From the location, timing, strength, and spectrum of HXR emission, we conclude that the prominence eruption is driven by the distinct events of magnetic reconnection occurring in the current sheet below the erupting prominence. These multi-wavelength observations also suggest that the localized magnetic reconnections associated with different evolutionary stages of the filament in the pre-eruption phase play an important role in destabilizing the active-region filament through the tether-cutting process, leading to large-scale eruption and X-class flare.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

MULTIPLE FAST MOLECULAR OUTFLOWS IN THE PRE-PLANETARY NEBULA CRL 618

CRL 618 is a well-studied pre-planetary nebula. It has multiple highly collimated optical lobes, fast molecular outflows along the optical lobes, and an extended molecular envelope that consists of a dense torus in the equator and a tenuous round halo. Here we present our observations of this source in CO J = 3-2 and HCN J = 4-3 obtained with the Submillimeter Array at up to ∼0.''3 resolutions. We spatially resolve the fast molecular outflow region previously detected in CO near the central star and find it to be composed of multiple outflows that have similar dynamical ages and are oriented along the different optical lobes. We also detect fast molecular outflows further away from the central star near the tips of the extended optical lobes and a pair of equatorial outflows inside the dense torus. We find that two episodes of bullet ejections in different directions are needed, one producing the fast molecular outflows near the central star and one producing the fast molecular outflows near the tips of the extended optical lobes. One possibility to launch these bullets is a magneto-rotational explosion of the stellar envelope.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

M-dwarf rapid rotators and the detection of relatively young multiple M-star systems

We have searched the Kepler light curves of ∼3900 M-star targets for evidence of periodicities that indicate, by means of the effects of starspots, rapid stellar rotation. Several analysis techniques, including Fourier transforms, inspection of folded light curves, 'sonograms', and phase tracking of individual modulation cycles, were applied in order to distinguish the periodicities due to rapid rotation from those due to stellar pulsations, eclipsing binaries, or transiting planets. We find 178 Kepler M-star targets with rotation periods, P {sub rot}, of <2 days, and 110 with P {sub rot} < 1 day. Some 30 of the 178 systems exhibit two or more independent short periods within the same Kepler photometric aperture, while several have 3 or more short periods. Adaptive optics imaging and modeling of the Kepler pixel response function for a subset of our sample support the conclusion that the targets with multiple periods are highly likely to be relatively young physical binary, triple, and even quadruple M star systems. We explore in detail the one object with four incommensurate periods all less than 1.2 days, and show that two of the periods arise from one of a close pair of stars, while the other two arise from the second star, which itself is probably a visual binary. If most of these M-star systems with multiple periods turn out to be bound M stars, this could prove a valuable way discovering young hierarchical M-star systems; the same approach may also be applicable to G and K stars. The ∼5% occurrence rate of rapid rotation among the ∼3900 M star targets is consistent with spin evolution models that include an initial contraction phase followed by magnetic braking, wherein a typical M star can spend several hundred Myr before spinning down to periods longer than 2 days.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Magnetohydrostatic equilibrium. II. Three-dimensional multiple open magnetic flux tubes in the stratified solar atmosphere

A system of multiple open magnetic flux tubes spanning the solar photosphere and lower corona is modeled analytically, within a realistic stratified atmosphere subject to solar gravity. This extends results for a single magnetic flux tube in magnetohydrostatic equilibrium, described in Gent et al. Self-similar magnetic flux tubes are combined to form magnetic structures, which are consistent with high-resolution observations. The observational evidence supports the existence of strands of open flux tubes and loops persisting in a relatively steady state. Self-similar magnetic flux tubes, for which an analytic solution to the plasma density and pressure distribution is possible, are combined. We calculate the appropriate balancing forces, applying to the equations of momentum and energy conservation to preserve equilibrium. Multiplex flux tube configurations are observed to remain relatively stable for up to a day or more, and it is our aim to apply our model as the background condition for numerical studies of energy transport mechanisms from the solar surface to the corona. We apply magnetic field strength, plasma density, pressure, and temperature distributions consistent with observational and theoretical estimates for the lower solar atmosphere. Although each flux tube is identical in construction apart from the location of the radial axis, combinations can be applied to generate a non-axisymmetric magnetic field with multiple non-uniform flux tubes. This is a considerable step forward in modeling the realistic magnetized three-dimensional equilibria of the solar atmosphere.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Particle energization during solar maximum: Diffusive shock acceleration at multiple shocks

We present a model for the acceleration of particles at multiple shocks using an approach related to box models. A distribution of particles is diffusively accelerated inside the box while simultaneously experiencing decompression through adiabatic expansion and losses from the convection and diffusion of particles out of the box by either the method used in Melrose and Pope and Pope and Melrose or by the approach introduced in Zank et al. where we solve the transport equation by a method analogous to operator splitting. The second method incorporates the additional loss terms of convection and diffusion and allows for the use of a variable time between shocks. We use a maximum injection energy (E{sub max}) appropriate for quasi-parallel and quasi-perpendicular shocks. We provide a preliminary application of the diffusive acceleration of particles by multiple shocks with frequencies appropriate for solar maximum.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Obliquities of Kepler stars: comparison of single- and multiple-transit systems

The stellar obliquity of a transiting planetary system can be constrained by combining measurements of the star's rotation period, radius, and projected rotational velocity. Here, we present a hierarchical Bayesian technique for recovering the obliquity distribution of a population of transiting planetary systems and apply it to a sample of 70 Kepler objects of interest. With ≈95% confidence, we find that the obliquities of stars with only a single detected transiting planet are systematically larger than those with multiple detected transiting planets. This suggests that a substantial fraction of Kepler's single-transiting systems represent dynamically hotter, less orderly systems than the 'pancake-flat' multiple-transiting systems.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

ON MULTIPLE RECONNECTION X-LINES AND TRIPOLAR PERTURBATIONS OF STRONG GUIDE MAGNETIC FIELDS

We report new multi-spacecraft Cluster observations of tripolar guide magnetic field perturbations at a solar wind reconnection exhaust in the presence of a guide field B{sub M} {sub }which is almost four times as strong as the reversing field B{sub L}. The novel tripolar field consists of two narrow regions of depressed B{sub M}, with an observed 7%–14% ΔB{sub M} magnitude relative to the external field, which are found adjacent to a wide region of enhanced B{sub M} within the exhaust. A stronger reversing field is associated with each B{sub M} depression. A kinetic reconnection simulation for realistic solar wind conditions and the observed strong guide field reveals that tripolar magnetic fields preferentially form across current sheets in the presence of multiple X-lines as magnetic islands approach one another and merge into fewer and larger islands. The simulated ΔB{sub M}/ΔX{sub N} over the normal width ΔX{sub N} between a B{sub M} minimum and the edge of the external region agree with the normalized values observed by Cluster. We propose that a tripolar guide field perturbation may be used to identify candidate regions containing multiple X-lines and interacting magnetic islands at individual solar wind current sheets with a strong guide field.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Observational signatures of planets in protoplanetary disks. I. Gaps opened by single and multiple young planets in disks

It has been suggested that the gaps and cavities recently discovered in transitional disks are opened by planets. To explore this scenario, we combine two-dimensional two fluid (gas + particle) hydrodynamical calculations with three-dimensional Monte Carlo Radiative Transfer simulations and study the observational signatures of gaps opened by one or several planets, making qualitative comparisons with observations. We find that a single planet as small as 0.2 M{sub J} can produce a deep gap at millimeter wavelengths and almost no features at near-infrared (NIR) wavelengths, while multiple planets can open up a few ×10 AU wide common gap at both wavelengths. Both the contrast ratio of the gaps and the wavelength dependence of the gap sizes are broadly consistent with data. We also confirm previous results that NIR gap sizes may be smaller than millimeter gap sizes due to dust–gas coupling and radiative transfer effects. When viewed at a moderate inclination angle, a physically circular on-centered gap could appear to be off-centered from the star due to shadowing. Planet-induced spiral arms are more apparent at NIR than at millimeter wavelengths. Overall, our results suggest that the planet-opening-gap scenario is a promising way to explain the origin of the transitional disks. Finally, inspired by the recent Atacama Large Millimeter Array release of the image of the HL Tau disk, we show that multiple narrow gaps, well separated by bright rings, can be opened by 0.2M{sub J} planets soon after their formation in a relatively massive disk.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

No evidence for multiple stellar populations in the low-mass galactic globular cluster E3

Multiple stellar populations are a widespread phenomenon among Galactic globular clusters. Even though the origin of the enriched material from which new generations of stars are produced remains unclear, it is likely that self-enrichment will be feasible only in clusters massive enough to retain this enriched material. We searched for multiple populations in the low mass (M∼1.4×10{sup 4} M{sub ⊙}) globular cluster E3, analyzing SOAR/Goodman multi-object spectroscopy centered on the blue cyanogen (CN) absorption features of 23 red giant branch stars. We find that the CN abundance does not present the typical bimodal behavior seen in clusters hosting multistellar populations, but rather a unimodal distribution that indicates the presence of a genuine single stellar population, or a level of enrichment much lower than in clusters that show evidence for two populations from high-resolution spectroscopy. E3 would be the first bona fide Galactic old globular cluster where no sign of self-enrichment is found.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

EVALUATING THE MORPHOLOGY OF THE LOCAL INTERSTELLAR MEDIUM: USING NEW DATA TO DISTINGUISH BETWEEN MULTIPLE DISCRETE CLOUDS AND A CONTINUOUS MEDIUM

Ultraviolet and optical spectra of interstellar gas along the lines of sight to nearby stars have been interpreted by Redfield and Linsky and previous studies as a set of discrete warm, partially ionized clouds each with a different flow vector, temperature, and metal depletion. Recently, Gry and Jenkins proposed a fundamentally different model consisting of a single cloud with nonrigid flows filling space out to 9 pc from the Sun that they propose better describes the local ISM. Here we test these fundamentally different morphological models against the spatially unbiased Malamut et al. spectroscopic data set, and find that the multiple cloud morphology model provides a better fit to both the new and old data sets. The detection of three or more velocity components along the lines of sight to many nearby stars, the presence of nearby scattering screens, the observed thin elongated structures of warm interstellar gas, and the likely presence of strong interstellar magnetic fields also support the multiple cloud model. The detection and identification of intercloud gas and the measurement of neutral hydrogen density in clouds beyond the Local Interstellar Cloud could provide future morphological tests.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

Multiple gamma lines from semi-annihilation

Hints in the Fermi data for a 130 GeV gamma line from the galactic center have ignited interest in potential gamma line signatures of dark matter. Explanations of this line based on dark matter annihilation face a parametric tension since they often rely on large enhancements of loop-suppressed cross sections. In this paper, we pursue an alternative possibility that dark matter gamma lines could arise from ''semi-annihilation'' among multiple dark sector states. The semi-annihilation reaction ψ{sub i}ψ{sub j} → ψ{sub k}γ with a single final state photon is typically enhanced relative to ordinary annihilation ψ{sub i}ψ-bar {sub i} → γγ into photon pairs. Semi-annihilation allows for a wide range of dark matter masses compared to the fixed mass value required by annihilation, opening the possibility to explain potential dark matter signatures at higher energies. The most striking prediction of semi-annihilation is the presence of multiple gamma lines, with as many as order N{sup 3} lines possible for N dark sector states, allowing for dark sector spectroscopy. A smoking gun signature arises in the simplest case of degenerate dark matter, where a strong semi-annihilation line at 130 GeV would be accompanied by a weaker annihilation line at 173 GeV. As a proof of principle, we construct two explicit models of dark matter semi-annihilation, one based on non-Abelian vector dark matter and the other based on retrofitting Rayleigh dark matter.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

CoLoRe: fast cosmological realisations over large volumes with multiple tracers

We present CoLoRe, a public software package to efficiently generate synthetic realisations of multiple cosmological surveys.CoLoRe can simulate the growth of structure with different degrees of accuracy, with the current implementation supporting lognormal fields, first, and second order Lagrangian perturbation theory.CoLoRe simulates the density field on an all-sky light-cone up to a desired maximum redshift, and uses it to generate multiple 2D and 3D maps: galaxy positions and velocities, lensing (shear, magnification, convergence), integrated Sachs-Wolfe effect, line intensity mapping, and line of sight skewers for simulations of the Lyman-α forest. We test the accuracy of the simulated maps against analytical theoretical predictions, and showcase its performance with a multi-survey simulation including DESI galaxies and quasars, LSST galaxies and lensing, and SKA intensity mapping and radio galaxies. We expect CoLoRe to be particularly useful in studies aiming to characterise the impact of systematics in multi-experiment analyses, quantify the covariance between different datasets, and test cross-correlation pipelines for near-future surveys.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Cosmology before noon with multiple galaxy populations

Near-future facilities observing the high-redshift universe (2 < z < 5) will have an opportunity to take advantage of "multi-tracer" cosmology by observing multiple tracers of the matter density field: Lyman alpha emitters (LAE), Lyman break galaxies (LBG), and CMB lensing κ. Here, in this work we use Fisher forecasts to investigate the effect of multi-tracers on next-generation facilities. In agreement with previous work, we show that multiple tracers improve constraints primarily from degeneracy breaking, instead of the traditional intuition of sample variance cancellation. Then, we forecast that for both BBN and CMB primary priors, the addition of lensing and LAEs onto a LBG-only sample will gain 25% or more in many parameters, with the largest gains being factor of ~ 10 improvement for f EDE . We include a preliminary approach towards modelling the impact of radiative transfer (RT) on forecasts involving LAEs by introducing a simplified model at linear theory level. Our results, albeit preliminary, show that while RT influences LAE-only forecasts strongly, its effect on composite multi-tracer forecasts is limited.

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