117 research outputs found
Spherical Harmonic Representation of Energetic Neutral Atom Flux Components Observed by IBEX
The Interstellar Boundary Explorer (IBEX) images the heliosphere by observing
energetic neutral atoms (ENAs). The IBEX-Hi instrument onboard IBEX provides
full-sky maps of ENA fluxes produced in the heliosphere and very local
interstellar medium (VLISM) through charge exchange of suprathermal ions with
interstellar neutral atoms. The first IBEX-Hi results showed that in addition
to the anticipated globally distributed flux (GDF), a narrow and bright
emission from a circular region in the sky, dubbed the IBEX ribbon, is visible
in all energy steps. While the GDF is mainly produced in the inner heliosheath,
ample evidence indicates that the ribbon forms outside the heliopause in the
regions where the interstellar magnetic field is perpendicular to the lines of
sight. The IBEX maps produced by the mission team distribute the observations
into rectangle pixels in ecliptic coordinates. The overlap
of the GDF and ribbon components complicates qualitative analyses of each
source. Here, we find the spherical harmonic representation of the IBEX maps,
separating the GDF and ribbon components. This representation describes the ENA
flux components in the sky without relying on any pixelization scheme. Using
this separation, we discuss the temporal evolution of each component over the
solar cycle. We find that the GDF is characterized by larger spatial scale
structures than the ribbon. However, we identify two isolated, small-scale
signals in the GDF region that require further study.Comment: 27 pages, 13 figures, v2 accepted for publication in ApJ
Investigating the IBEX Ribbon Structure a Solar Cycle Apart
A Ribbon of enhanced energetic neutral atom (ENA) emissions was discovered by
the Interstellar Boundary Explorer (IBEX) in 2009, redefining our understanding
of the heliosphere boundaries and the physical processes occurring at the
interstellar interface. The Ribbon signal is intertwined with that of a
globally distributed flux (GDF) that spans the entire sky. To a certain extent,
Ribbon separation methods enabled examining its evolution independent of the
underlying GDF. Observations over a full solar cycle revealed the Ribbon's
evolving nature, with intensity variations closely tracking those of the solar
wind (SW) structure after a few years delay accounting for the SW-ENA recycling
process. In this work, we examine the Ribbon structure, namely, its ENA fluxes,
angular extent, width, and circularity properties for two years, 2009 and 2019,
representative of the declining phases of two adjacent solar cycles. We find
that, (i) the Ribbon ENA fluxes have recovered in the nose direction and south
of it down to ~ 25{\deg} (for energies below 1.7 keV) and not at mid and high
ecliptic latitudes; (ii) The Ribbon width exhibits significant variability as a
function of azimuthal angle; (iii) Circularity analysis suggests that the 2019
Ribbon exhibits a statistically consistent radius with that in 2009. The
Ribbon's partial recovery is aligned with the consensus of a heliosphere with
its closest point being southward of the nose region. The large variability of
the Ribbon width as a function of Azimuth in 2019 compared to 2009 is likely
indicative of small-scale processes within the Ribbon.Comment: 5 figure
Individual Differences in Eye-Movements During Reading: Working Memory and Speed-of-Processing Effects
Mathematical models of eye-movement control do not yet incorporate individual differences as a source of variation in reading. These models nonetheless provide an excellent foundation for describing and explaining how and why patterns of eye-movements differ across readers (e.g., Rayner et al., 2006). We focus in this article on two aspects of individual variation: global processing speed (e.g., Salthouse, 1996) and working-memory capacity (e.g., Just & Carpenter, 1992). Using Hierarchical Linear Modeling (HLM) (Raudenbush & Bryk, 2001), we tested the extent to which overall reading speed and working-memory capacity moderate the degree to which syntactic and semantic information affect fixation times. We found that working-memory capacity interacted with sentence-characteristic variables only when processing speed was not included in the model
Data handling with SAM and art at the NOνA experiment
During operations, NOvA produces between 5,000 and 7,000 raw files per day with peaks in excess of 12,000. These files must be processed in several stages to produce fully calibrated and reconstructed analysis files. In addition, many simulated neutrino interactions must be produced and processed through the same stages as data. To accommodate the large volume of data and Monte Carlo, production must be possible both on the Fermilab grid and on off-site farms, such as the ones accessible through the Open Science Grid. To handle the challenge of cataloging these files and to facilitate their off-line processing, we have adopted the SAM system developed at Fermilab. SAM indexes files according to metadata, keeps track of each file's physical locations, provides dataset management facilities, and facilitates data transfer to off-site grids. To integrate SAM with Fermilab's art software framework and the NOvA production workflow, we have developed methods to embed metadata into our configuration files, art files, and standalone ROOT files. A module in the art framework propagates the embedded information from configuration files into art files, and from input art files to output art files, allowing us to maintain a complete processing history within our files. Embedding metadata in configuration files also allows configuration files indexed in SAM to be used as inputs to Monte Carlo production jobs. Further, SAM keeps track of the input files used to create each output file. Parentage information enables the construction of self-draining datasets which have become the primary production paradigm used at NOvA. In this paper we will present an overview of SAM at NOvA and how it has transformed the file production framework used by the experiment
Constraining the Evolution of the Proton Distribution Function in the Heliotail
We use Interstellar Boundary Explorer (IBEX) measurements of energetic neutral atoms (ENAs) to constrain the proton (mostly pickup ion, PUI) distribution in the heliotail. In our previous study, we solved the Parker transport equation and found that the velocity diffusion coefficient D(v) for PUIs is approximately D(v) ~ 1.1 × 10⁻⁸ km² s⁻³ (v/v₀)¹̇͘͘·³, assuming the initial proton distribution processed by the termination shock (TS), fp,₀, is a kappa distribution with kappa index κp,₀ = 1.63. In this study, we test different forms for f p,₀. We find that if f p,₀ is kappa-distributed and D(v) = D₀(v/v₀)¹̇͘͘·³, any kappa index in the range 1.5 2 keV compared to IBEX. However, using a fully kinetic particle-in-cell simulation to process a PUI filled-shell across the TS yields ENA spectra consistent with IBEX, reinforcing the significance of self-consistent, preferential PUI heating and diffusion at the TS. Interestingly, an upstream PUI distribution inferred from the particle-in-cell simulation to reproduce Voyager 2 observations of the nose-ward TS is inconsistent with IBEX observations from the heliotail, suggesting differences in the upstream PUI distribution or TS properties
Interstellar Conditions Deduced from Interstellar Neutral Helium Observed by IBEX and Global Heliosphere Modeling
In situ observations of interstellar neutral (ISN) helium atoms by the
IBEX-Lo instrument onboard the Interstellar Boundary Explorer (IBEX) mission
are used to determine the velocity and temperature of the pristine very local
interstellar medium (VLISM). Most ISN helium atoms penetrating the heliosphere,
known as the primary population, originate in the pristine VLISM. As the
primary atoms travel through the outer heliosheath, they charge exchange with
He ions in slowed and compressed plasma creating the secondary population.
With more than 2.4 million ISN helium atoms sampled by IBEX during ISN seasons
2009-2020, we compare the observations with predictions of a parametrized model
of ISN helium transport in the heliosphere. We account for the filtration of
ISN helium atoms at the heliospheric boundaries by charge exchange and elastic
collisions. We examine the sensitivity of the ISN helium fluxes to the
interstellar conditions described by the pristine VLISM velocity, temperature,
magnetic field, and composition. We show that comprehensive modeling of the
filtration processes is critical for interpreting ISN helium observations, as
the change in the derived VLISM conditions exceeds the statistical
uncertainties when accounting for these effects. The pristine VLISM parameters
found by this analysis are the flow speed (26.6 km s), inflow direction
in ecliptic coordinates (255.7, 5.04), temperature (7350 K),
and B-V plane inclination to the ecliptic plane (53.7). The derived
pristine VLISM He density is cm. Additionally, we
show a strong correlation between the interstellar plasma density and magnetic
field strength deduced from these observations.Comment: 13 pages, 3 figures, 2 tables, accepted for publication in Ap
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