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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 1,297 records · Page 72
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

3D WHOLE-PROMINENCE FINE STRUCTURE MODELING. II. PROMINENCE EVOLUTION

We use the new three-dimensional (3D) whole-prominence fine structure model to study the evolution of prominences and their fine structures in response to changes in the underlying photospheric magnetic flux distribution. The applied model combines a detailed 3D prominence magnetic field configuration with a realistic description of the prominence plasma distributed along multiple fine structures. In addition, we utilize an approximate Hα visualization technique to study the evolution of the visible cool prominence plasma both in emission (prominence) and absorption (filament). We show that the initial magnetic field configuration of the modeled prominence is significantly disturbed by the changing position of a single polarity of a magnetic bipole as the bipole is advected toward the main body of the filament. This leads to the creation of a barb, which becomes the dominant feature visible in the synthetic Hα images of both the prominence and filament views. The evolution of the bipole also creates conditions that lead to the disappearance and reappearance of large portions of the main body. We also show that an arch-like region containing a dark void (a bubble) can be naturally produced in the synthetic prominence Hα images. While not visible in terms of the magnetic field lines, it is due to a lack of Hα emission from low-pressure, low-density plasma located in shallow magnetic dips lying along the lines of sight intersecting the dark void. In addition, a quasi-vertical small-scale feature consisting of short and deep dips, piled one above the other, is produced.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

CONSTRAINT ON LIGHT DIPOLE DARK MATTER FROM HELIOSEISMOLOGY

We investigate the effects of a magnetic dipole moment of asymmetric dark matter (DM) in the evolution of the Sun. The dipole interaction can lead to a sizable DM scattering cross section even for light DM, and asymmetric DM can lead to a large DM number density in the Sun. We find that solar model precision tests, using as diagnostic the sound speed profile obtained from helioseismology data, exclude dipolar DM particles with a mass larger than 4.3 GeV and magnetic dipole moment larger than 1.6 × 10{sup –17} e cm.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ON THE CAUSE OF SOLAR-LIKE EQUATORWARD MIGRATION IN GLOBAL CONVECTIVE DYNAMO SIMULATIONS

We present results from four convectively driven stellar dynamo simulations in spherical wedge geometry. All of these simulations produce cyclic and migrating mean magnetic fields. Through detailed comparisons, we show that the migration direction can be explained by an αΩ dynamo wave following the Parker-Yoshimura rule. We conclude that the equatorward migration in this and previous work is due to a positive (negative) α effect in the northern (southern) hemisphere and a negative radial gradient of Ω outside the inner tangent cylinder of these models. This idea is supported by a strong correlation between negative radial shear and toroidal field strength in the region of equatorward propagation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

MAGNETIC FIELD STRUCTURE IN THE FLATTENED ENVELOPE AND JET IN THE YOUNG PROTOSTELLAR SYSTEM HH 211

HH 211 is a young Class 0 protostellar system with a flattened envelope, a possible rotating disk, and a collimated jet. We have mapped it with the Submillimeter Array in the 341.6 GHz continuum and SiO J = 8-7 at ∼0.''6 resolution. The continuum traces the thermal dust emission in the flattened envelope and the possible disk. Linear polarization is detected in the continuum in the flattened envelope. The field lines implied from the polarization have different orientations, but they are not incompatible with current gravitational collapse models, which predict a different orientation depending on the region/distance. Also, we might have detected for the first time polarized SiO line emission in the jet due to the Goldreich-Kylafis effect. Observations at higher sensitivity are needed to determine the field morphology in the jet.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

IMAGING AND SPECTROSCOPIC OBSERVATIONS OF MAGNETIC RECONNECTION AND CHROMOSPHERIC EVAPORATION IN A SOLAR FLARE

Magnetic reconnection is believed to be the dominant energy release mechanism in solar flares. The standard flare model predicts both downward and upward outflow plasmas with speeds close to the coronal Alfvén speed. Yet, spectroscopic observations of such outflows, especially the downflows, are extremely rare. With observations of the newly launched Interface Region Imaging Spectrograph (IRIS), we report the detection of a greatly redshifted (∼125 km s{sup –1} along the line of sight) Fe XXI 1354.08 Å emission line with a ∼100 km s{sup –1} nonthermal width at the reconnection site of a flare. The redshifted Fe XXI feature coincides spatially with the loop-top X-ray source observed by RHESSI. We interpret this large redshift as the signature of downward-moving reconnection outflow/hot retracting loops. Imaging observations from both IRIS and the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory also reveal the eruption and reconnection processes. Fast downward-propagating blobs along these loops are also found from cool emission lines (e.g., Si IV, O IV, C II, Mg II) and images of AIA and IRIS. Furthermore, the entire Fe XXI line is blueshifted by ∼260 km s{sup –1} at the loop footpoints, where the cool lines mentioned above all exhibit obvious redshift, a result that is consistent with the scenario of chromospheric evaporation induced by downward-propagating nonthermal electrons from the reconnection site.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Systematic exploration of heavy element nucleosynthesis in protomagnetar outflows

ABSTRACT We study the nucleosynthesis products in neutrino-driven winds from rapidly rotating, highly magnetized and misaligned protomagnetars using the nuclear reaction network SkyNet. We adopt a semi-analytic parametrized model for the protomagnetar and systematically study the capabilities of its neutrino-driven wind for synthesizing nuclei and eventually producing ultra-high energy cosmic rays (UHECRs). We find that for neutron-rich outflows (Ye < 0.5), synthesis of heavy elements ($\overline{A}\sim 20-65$) is possible during the first $\sim 10\, {\rm s}$ of the outflow, but these nuclei are subjected to composition-altering photodisintegration during the epoch of particle acceleration at the dissipation radii. However, after the first $\sim 10\, {\rm s}$ of the outflow, nucleosynthesis reaches lighter elements ($\overline{A}\sim 10-50$) that are not subjected to subsequent photodisintegration. For proton-rich (Ye ≥ 0.5) outflows, synthesis is more limited ($\overline{A}\sim 4-15$). These suggest that while protomagnetars typically do not synthesize nuclei heavier than second r-process peak elements, they are intriguing sources of intermediate/heavy mass UHECRs. For all configurations, the most rapidly rotating protomagnetars are more conducive for nucleosynthesis with a weaker dependence on the magnetic field strength.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

On the nature of radio filaments near the Galactic Centre

We suggest that narrow, long radio filaments near the Galactic Centre arise as kinetic jets – streams of high-energy particles escaping from ram pressure confined pulsar wind nebulae (PWNe). The reconnection between the PWN and interstellar magnetic field allows pulsar wind particles to escape, creating long narrow features. They are the low-frequency analogues of kinetic jets seen around some fast-moving pulsars, such as The Guitar and The Lighthouse PWNe. The radio filaments trace a population of pulsars also responsible for the Fermi GeV excess produced by the Inverse Compton scattering by the pulsar wind particles. The magnetic flux tubes are stretched radially by the large-scale Galactic winds. In addition to PWNe accelerated particles can be injected at supernovae remnants. The model predicts variations of the structure of the largest filaments on scales of ~dozens of years – smaller variations can occur on shorter time-scales. We also encourage targeted observations of the brightest sections of the filaments and of the related unresolved point sources in search of the powering PWNe and pulsars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Cycloidal paths in physics as superpositions of translational and rotational motions

Cycloidal paths are ubiquitous in physics. Here, we show that representative cycloidal paths in physics can be described as superpositions of translations and rotations of a point through space. Using this unifying principle, the parametric equations of the path of a point on a rolling disk are derived for rolling without slipping, rolling with frictionless slipping, and when kinetic solid-on-solid friction is present during rolling with slipping. In a similar way, the parametric equations versus time for the orbit with respect to a star of a moon in a circular orbit about a planet that is in a circular orbit about a star are derived, where the orbits are coplanar. The parametric equations versus time for the path of the magnetization vector during undamped electron-spin resonance are found using the same principle, which show that cycloidal paths can occur under specified conditions.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2016

THE NONLINEAR EVOLUTION OF A TWIST IN A MAGNETIC SHOCKTUBE

The interaction between a small twist and a horizontal chromospheric shocktube is investigated. The magnetic flux tube is modeled using 1.5-D magnetohydrodynamics. The presence of a supersonic yet sub-Alfvénic flow along the flux tube allows the Alfvénic pulse driven at the photospheric boundary to become trapped and amplified between the stationary shock front and photosphere. The amplification of the twist leads to the formation of slow and fast shocks. The pre-existing stationary shock is destabilized and pushed forward as it merges with the slow shock. The propagating fast shock extracts the kinetic energy of the flow and launches rapid twists of 10–15 km s{sup −1} upon each reflection. A cavity is formed between the slow and fast shocks where the flux tube becomes globally twisted within less than an hour. The resultant highly twisted magnetic flux tube is similar to those prone to kink instabilities, which may be responsible for solar eruptions. The generated torsional flux is calculated.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

FORMATION AND PLASMA CIRCULATION OF SOLAR PROMINENCES

Solar prominences are long-lived cool and dense plasma curtains in the hot and rarefied outer solar atmosphere or corona. The physical mechanism responsible for their formation and especially for their internal plasma circulation has been uncertain for decades. The observed ubiquitous downflows in quiescent prominences are difficult to interpret because plasma with high conductivity seems to move across horizontal magnetic field lines. Here we present three-dimensional numerical simulations of prominence formation and evolution in an elongated magnetic flux rope as a result of in situ plasma condensations fueled by continuous plasma evaporation from the solar chromosphere. The prominence is born and maintained in a fragmented, highly dynamic state with continuous reappearance of multiple blobs and thread structures that move mainly downward, dragging along mass-loaded field lines. The circulation of prominence plasma is characterized by the dynamic balance between the drainage of prominence plasma back to the chromosphere and the formation of prominence plasma via continuous condensation. Plasma evaporates from the chromosphere, condenses into the prominence in the corona, and drains back to the chromosphere, establishing a stable chromosphere–corona plasma cycle. Synthetic images of the modeled prominence with the Solar Dynamics Observatory Atmospheric Imaging Assembly closely resemble actual observations, with many dynamical threads underlying an elliptical coronal cavity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

TIME-DEPENDENT SUPPRESSION OF OSCILLATORY POWER IN EVOLVING SOLAR MAGNETIC FIELDS

Oscillation amplitudes are generally smaller within magnetically active regions like sunspots and plage when compared to their surroundings. Such magnetic features, when viewed in spatially resolved power maps, appear as regions of suppressed power due to reductions in the oscillation amplitudes. Employing high spatial- and temporal-resolution observations from the Dunn Solar Telescope (DST) in New Mexico, we study the power suppression in a region of evolving magnetic fields adjacent to a pore. By utilizing wavelet analysis, we study for the first time how the oscillatory properties in this region change as the magnetic field evolves with time. Image sequences taken in the blue continuum, G-band, Ca ii K, and H α filters were used in this study. It is observed that the suppression found in the chromosphere occupies a relatively larger area, confirming previous findings. Also, the suppression is extended to structures directly connected to the magnetic region, and is found to get enhanced as the magnetic field strength increased with time. The dependence of the suppression on the magnetic field strength is greater at longer periods and higher formation heights. Furthermore, the dominant periodicity in the chromosphere was found to be anti-correlated with increases in the magnetic field strength.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A NEW TECHNIQUE FOR THE PHOTOSPHERIC DRIVING OF NON-POTENTIAL SOLAR CORONAL MAGNETIC FIELD SIMULATIONS

In this paper, we develop a new technique for driving global non-potential simulations of the Sun’s coronal magnetic field solely from sequences of radial magnetic maps of the solar photosphere. A primary challenge to driving such global simulations is that the required horizontal electric field cannot be uniquely determined from such maps. We show that an “inductive” electric field solution similar to that used by previous authors successfully reproduces specific features of the coronal field evolution in both single and multiple bipole simulations. For these cases, the true solution is known because the electric field was generated from a surface flux-transport model. The match for these cases is further improved by including the non-inductive electric field contribution from surface differential rotation. Then, using this reconstruction method for the electric field, we show that a coronal non-potential simulation can be successfully driven from a sequence of ADAPT maps of the photospheric radial field, without including additional physical observations which are not routinely available.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

FRiED: A NOVEL THREE-DIMENSIONAL MODEL OF CORONAL MASS EJECTIONS

We present a novel three-dimensional (3D) model of coronal mass ejections (CMEs) that unifies all key evolutionary aspects of CMEs and encapsulates their 3D magnetic field configuration. This fully analytic model is capable of reproducing the global geometrical shape of a CME with all major deformations taken into account, i.e., deflection, rotation, expansion, “pancaking,” front flattening, and rotational skew. Encapsulation of 3D magnetic structure allows the model to reproduce in-situ measurements of magnetic field for trajectories of spacecraft-CME encounters of any degree of complexity. As such, the model can be used single-handedly for the consistent analysis of both remote and in-situ observations of CMEs at any heliocentric distance. We demonstrate the latter by successfully applying the model for the analysis of two CMEs.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Timing Solution and Single-pulse Properties for Eight Rotating Radio Transients

Rotating radio transients (RRATs), loosely defined as objects that are discovered through only their single pulses, are sporadic pulsars that have a wide range of emission properties. For many of them, we must measure their periods and determine timing solutions relying on the timing of their individual pulses, while some of the less sporadic RRATs can be timed by using folding techniques as we do for other pulsars. Here, based on Parkes and Green Bank Telescope (GBT) observations, we introduce our results on eight RRATs including their timing-derived rotation parameters, positions, and dispersion measures (DMs), along with a comparison of the spin-down properties of RRATs and normal pulsars. Using data for 24 RRATs, we find that their period derivatives are generally larger than those of normal pulsars, independent of any intrinsic correlation with period, indicating that RRATs’ highly sporadic emission may be associated with intrinsically larger magnetic fields. We carry out Lomb–Scargle tests to search for periodicities in RRATs’ pulse detection times with long timescales. Periodicities are detected for all targets, with significant candidates of roughly 3.4 hr for PSR J1623−0841 and 0.7 hr for PSR J1839−0141. We also analyze their single-pulse amplitude distributions, finding that log-normal distributions provide the best fits, as is the case for most pulsars. However, several RRATs exhibit power-law tails, as seen for pulsars emitting giant pulses. This, along with consideration of the selection effects against the detection of weak pulses, imply that RRAT pulses generally represent the tail of a normal intensity distribution.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

How Far Is Quasar UV/Optical Variability from a Damped Random Walk at Low Frequency?

Studies have shown that UV/optical light curves of quasars can be described using the prevalent damped random walk (DRW) model, also known as the Ornstein–Uhlenbeck process. A white noise power spectral density (PSD) is expected at low frequency in this model; however, a direct observational constraint to the low-frequency PSD slope is difficult due to the limited lengths of the light curves available. Meanwhile, quasars show scatter in their DRW parameters that is too large to be attributed to uncertainties in the measurements and dependence on the variation of known physical factors. In this work we present simulations showing that, if the low-frequency PSD deviates from the DRW, the red noise leakage can naturally produce large scatter in the variation parameters measured from simulated light curves. The steeper the low-frequency PSD slope, the larger scatter we expect. Based on observations of SDSS Stripe 82 quasars, we find that the low-frequency PSD slope should be no steeper than −1.3. The actual slope could be flatter, which consequently requires that the quasar variabilities should be influenced by other unknown factors. We speculate that the magnetic field and/or metallicity could be such additional factors.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Dipole Magnetic Field and Spin-down Evolutions of the High Braking Index Pulsar PSR J1640–4631

In this work, we interpreted the high braking index of PSR J1640−4631 with a combination of the magneto-dipole radiation and dipole magnetic field decay models. By introducing a mean rotation energy conversion coefficient ζ-bar , the ratio of the total high-energy photon energy to the total rotation energy loss in the whole life of the pulsar, and combining the pulsar’s high-energy and timing observations with a reliable nuclear equation of state, we estimate the pulsar’s initial spin period, P{sub 0}∼(17--44) ms, corresponding to the moment of inertia I∼(0.8--2.1)×10{sup 45} g cm{sup 2}. Assuming that PSR J1640−4631 has experienced a long-term exponential decay of the dipole magnetic field, we calculate the true age t{sub age}, the effective magnetic field decay timescale τ{sub D}, and the initial surface dipole magnetic field at the pole B{sub p}(0) of the pulsar to be 2900−3100 yr, 1.07(2)×10{sup 5} yr, and (1.84--4.20)×10{sup 13} G, respectively. The measured braking index of n=3.15(3) for PSR J1640−4631 is attributed to its long-term dipole magnetic field decay and a low magnetic field decay rate, dB{sub p}/dt∼−(1.66--3.85)×10{sup 8} G yr{sup −1}. Our model can be applied to both the high braking index (n>3) and low braking index (n<3) pulsars, tested by the future polarization, timing, and high-energy observations of PSR J1640−4631.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

Possible ambiguities in the equation of state for neutron stars

We addressed possible ambiguities on the properties of neutron stars (NSs) estimated in theoretical sides. First, roles of hyperons inside the NS are discussed through various relativistic mean field (RMF) theories. In particular, the extension of SU(6) spin-flavor symmetry to SU(3) flavor symmetry is shown to give rise to the increase of hyperon threshold density, similarly to the Fock term effects in RMF theories. As a result, about 2.0 solar mass is obtained with the hyperons. Second, the effect by the modified f(R) gravity, which leaves a room for the dark energy in the Einstein equation to be taken into account, is discussed for the NS in a strong magnetic field (MF). Our results show that the modified gravity with the Kaluza-Klein electro-magnetism theory expanded in terms of a length scale parameter may reasonably describe the NS in strong MF, so called magnetar. Even the super-soft equation of state is shown to be revived by the modified f(R) gravity.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

NEAR-INFRARED CIRCULAR POLARIZATION IMAGES OF NGC 6334-V

We present results from deep imaging linear and circular polarimetry of the massive star-forming region NGC 6334-V. These observations show high degrees of circular polarization (CP), as much as 22% in the K{sub s} band, in the infrared nebula associated with the outflow. The CP has an asymmetric positive/negative pattern and is very extended ({approx}80'' or 0.65 pc). Both the high CP and its extended size are larger than those seen in the Orion CP region. Three-dimensional Monte Carlo light-scattering models are used to show that the high CP may be produced by scattering from the infrared nebula followed by dichroic extinction by an optically thick foreground cloud containing aligned dust grains. Our results show not only the magnetic field orientation of around young stellar objects, but also the structure of circumstellar matter such as outflow regions and their parent molecular cloud along the line of sight. The detection of the large and extended CP in this source and the Orion nebula may imply the CP origin of the biological homochirality on Earth.

79 ASTRONOMY AND ASTROPHYSICS↗