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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 991 records · Page 55
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DOE OSTI2016

IRAS 16253–2429: THE FIRST PROTO-BROWN DWARF BINARY CANDIDATE IDENTIFIED THROUGH THE DYNAMICS OF JETS

The formation mechanism of brown dwarfs (BDs) is one of the long-standing problems in star formation because the typical Jeans mass in molecular clouds is too large to form these substellar objects. To answer this question, it is crucial to study a BD in the embedded phase. IRAS 16253–2429 is classified as a very low-luminosity object (VeLLO) with an internal luminosity of <0.1 L {sub ⊙}. VeLLOs are believed to be very low-mass protostars or even proto-BDs. We observed the jet/outflow driven by IRAS 16253–2429 in CO (2–1), (6–5), and (7–6) using the IRAM 30 m and Atacama Pathfinder Experiment telescopes and the Submillimeter Array (SMA) in order to study its dynamical features and physical properties. Our SMA map reveals two protostellar jets, indicating the existence of a proto-binary system as implied by the precessing jet detected in H{sub 2} emission. We detect a wiggling pattern in the position–velocity diagrams along the jet axes, which is likely due to the binary orbital motion. Based on this information, we derive the current mass of the binary as ∼0.032 M{sub ⊙}. Given the low envelope mass, IRAS 16253–2429 will form a binary that probably consist of one or two BDs. Furthermore, we found that the outflow force as well as the mass accretion rate are very low based on the multi-transition CO observations, which suggests that the final masses of the binary components are at the stellar/substellar boundary. Since IRAS 16253 is located in an isolated environment, we suggest that BDs can form through fragmentation and collapse, similar to low-mass stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

High-speed bullet ejections during the AGB-to-planetary nebula transition: HST observations of the carbon star, v hydrae

The well-studied carbon star, V Hya, showing evidence for high-speed, collimated outflows and dense equatorial structures, is a key object in the study of the poorly understood transition of AGB stars into aspherical planetary nebulae. Using the Space Telescope Imaging Spectrograph instrument on board the Hubble Space Telescope, we have obtained high spatial-resolution long-slit optical spectra of V Hya that show high-velocity emission in [S ii] and [Fe ii] lines. Our data set, spanning three epochs spaced apart by a year during each of two periods (in 2002–2004 and 2011–2013), shows that V Hya ejects high-speed (∼200–250 km s{sup −1}) bullets once every ∼8.5 years. The ejection axis flip–flops around a roughly eastern direction, both in and perpendicular to the sky-plane, and the radial velocities of the ejecta also vary in concert between low and high values. We propose a model in which the bullet ejection is associated with the periastron passage of a binary companion in an eccentric orbit around V Hya with an orbital period of ∼8.5 years. The flip–flop phenomenon is likely the result of collimated ejection from an accretion disk (produced by gravitational capture of material from the primary) that is warped and precessing, and/or that has a magnetic field that is misaligned with that of the companion or the primary star. We show how a previously observed 17 year period in V Hya’s light-cycle can also be explained in our model. Additionally, we describe how the model proposed here can be extended to account for multipolar nebulae.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

A perturbative analysis of synchrotron spectral index variation over the microwave sky

In this paper, we implement a perturbative approach, first proposed by Bouchet and Gispert, to estimate the variation of the spectral index of galactic polarized synchrotron emission, using a linear combination of simulated Stokes Q polarization maps of selected frequency bands from WMAP and Planck observations on a region of sky dominated by the synchrotron Stokes Q signal. We find that a first order perturbative analysis recovers the input spectral index map well. Along with the spectral index variation map, our method provides a fixed reference index, β-hat {sub 0s}, over the sky portion being analyzed. Using Monte-Carlo simulations, we find that 〈 β-hat {sub 0s}〉=−2.84±0.01, which matches very closely with the position of a peak at β{sub s}(p)=−2.85 of the empirical probability density function of input synchrotron indices obtained from the same sky region. For thermal dust, the mean recovered spectral index 〈 β-hat {sub d}〉=2.00±0.004 from simulations, matches very well with the spatially fixed input thermal dust spectral index β{sub d}=2.00. As accompanying results of the method, we reconstruct cosmic microwave background, thermal dust, and a synchrotron template components with fixed spectral indices over the entire sky region. We use, in our analysis, full pixel–pixel noise covariance matrices of all frequency bands, estimated from the sky region being analyzed. The perturbative technique of this work (1) can build a model with an arbitrary but sufficient degree of accuracy (and precession) as allowed by the data and (2) can produce maximum likelihood estimators for reference indices and templates asymptotically.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Giant Metrewave Radio Telescope Observations of Head–Tail Radio Galaxies

We present results from a study of seven large known head–tail radio galaxies based on observations using the Giant Metrewave Radio Telescope at 240 and 610 MHz. These observations are used to study the radio morphologies and distribution of the spectral indices across the sources. The overall morphology of the radio tails of these sources is suggestive of random motions of the optical host around the cluster potential. The presence of multiple bends and wiggles in several head–tail sources is possibly due to the precessing radio jets. We find steepening of the spectral index along the radio tails. The prevailing equipartition magnetic field also decreases along the radio tails of these sources. These steepening trends are attributed to the synchrotron aging of plasma toward the ends of the tails. The dynamical ages of these sample sources have been estimated to be ∼10{sup 8} yr, which is a factor of six more than the age estimates from the radiative losses due to synchrotron cooling.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2018

Obliquity Variations of Habitable Zone Planets Kepler-62f and Kepler-186f

Obliquity variability could play an important role in the climate and habitability of a planet. Orbital modulations caused by planetary companions and the planet’s spin axis precession due to the torque from the host star may lead to resonant interactions and cause large-amplitude obliquity variability. Here we consider the spin axis dynamics of Kepler-62f and Kepler-186f, both of which reside in the habitable zone around their host stars. Using N-body simulations and secular numerical integrations, we describe their obliquity evolution for particular realizations of the planetary systems. We then use a generalized analytic framework to characterize regions in parameter space where the obliquity is variable with large amplitude. We find that the locations of variability are fine-tuned over the planetary properties and system architecture in the lower-obliquity regimes (≲40°). As an example, assuming a rotation period of 24 hr, the obliquities of both Kepler-62f and Kepler-186f are stable below ∼40°, whereas the high-obliquity regions (60°–90°) allow moderate variabilities. However, for some other rotation periods of Kepler-62f or Kepler-186f, the lower-obliquity regions could become more variable owing to resonant interactions. Even small deviations from coplanarity (e.g., mutual inclinations ∼3°) could stir peak-to-peak obliquity variations up to ∼20°. Undetected planetary companions and/or the existence of a satellite could also destabilize the low-obliquity regions. In all cases, the high-obliquity region allows for moderate variations, and all obliquities corresponding to retrograde motion (i.e., >90°) are stable.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Late Delivery of Nitrogen to the Earth

Atmospheric nitrogen may be a necessary ingredient for the habitability of a planet as its presence helps to prevent water loss from a planet. The present-day nitrogen isotopic ratio, {sup 15}N/{sup 14}N, in the Earth’s atmosphere is a combination of the primitive Earth’s ratio and the ratio that might have been delivered in comets and asteroids. Asteroids have a nitrogen isotopic ratio that is close to the Earth’s. This indicates either a similar formation environment to the Earth or that the main source of nitrogen was delivery by asteroids. However, according to geological records, the Earth’s atmosphere could have been enriched in {sup 15}N during the Archean era. Comets have a higher {sup 15}N/{sup 14}N ratio than the current atmosphere of the Earth, and we find that about 5% ∼ 10% of nitrogen in the atmosphere of the Earth may have been delivered by comets to explain the current atmosphere of the Earth or the enriched {sup 15}N atmosphere of the Earth. We model the evolution of the radii of the snow lines of molecular nitrogen and ammonia in a protoplanetary disk and find that both have radii that put them farther from the Sun than the main asteroid belt. With an analytic secular resonance model and N-body simulations we find that the ν {sub 8} apsidal precession secular resonance with Neptune, which is located in the Kuiper Belt, is a likely origin for the nitrogen-delivering comets that impact the Earth.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2019

Shape and Rotational Motion Models for Tumbling and Monolithic Asteroid 2012 TC{sub 4}: High Time Resolution Light Curve with the Tomo-e Gozen Camera

We present visible and near-infrared observations of a near-Earth object (NEO), 2012 TC{sub 4}. The NEO 2012 TC{sub 4} approached close to Earth at a distance of about 50,000 km in 2017 October. This close approach provided a practical exercise for planetary defense. This apparition was also an appropriate opportunity to investigate 2012 TC{sub 4}, which is a monolithic asteroid. We conducted the observation campaign of 2012 TC{sub 4} using six small- and medium-sized telescopes. The multiband photometry analysis showed the taxonomic class of 2012 TC{sub 4} to be an X type. In particular, we successfully obtained the high time resolution light curve of 2012 TC{sub 4} with the Tomo-e Gozen camera, which is the world’s first wide-field CMOS camera, mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The shape and rotational motion models of 2012 TC{sub 4} were derived from the light curve. When 2012 TC{sub 4} was assumed to be a triaxial ellipsoid, the rotational and precession periods were 8.47 ± 0.01 minutes and 12.25 ± 0.01 minutes, respectively, with the long-axis mode. This indicates that 2012 TC{sub 4} is a tumbling and monolithic asteroid. The shape models showed the plausible axial lengths to be 6.2 × 8.0 × 14.9 m or 3.3 × 8.0 × 14.3 m. The flattened and elongated shape indicates that 2012 TC{sub 4} is a fragment produced by an impact event. We also estimated the excitation timescale, which implied that the impact event happened within ∼3 × 10{sup 5} yr and 2012 TC{sub 4} has a fresh surface.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Secular Eccentricity Oscillations in Axisymmetric Disks of Eccentric Orbits

Massive bodies undergo orbital eccentricity oscillations when embedded in an axisymmetric disk of smaller mass orbits. These eccentricity oscillations are driven by secular torques that seek to equalize the apsidal precession rates of all the orbits in the disk. We investigate this mechanism within the context of detached objects in the outer solar system, but we find that the oscillation timescale is too long for it to be dynamically important. It could however be interesting for phenomenon a bit farther from home, namely, feeding supermassive black holes and polluting the surfaces of white dwarf stars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2020

Giant-planet Influence on the Collective Gravity of a Primordial Scattered Disk

Axisymmetric disks of high-eccentricity, low-mass bodies on near-Keplerian orbits are unstable to an out-of-plane buckling. This “inclination instability” exponentially grows the orbital inclinations, raises perihelion distances, and clusters in the argument of perihelion. Here we examine the instability in a massive primordial scattered disk including the orbit-averaged gravitational influence of the giant planets. We show that differential apsidal precession induced by the giant planets will suppress the inclination instability unless the primordial mass is ≳20 Earth masses. We also show that the instability should produce a “perihelion gap” at semimajor axes of hundreds of astronomical units, as the orbits of the remnant population are more likely to have extremely large perihelion distances (O(100 au)) than intermediate values.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

Spin Change of Asteroid 2012 TC4 Probably by Radiation Torques

Asteroid 2012 TC4 is a small (∼10 m) near-Earth object that was observed during its Earth close approaches in 2012 and 2017. Earlier analyses of light curves revealed its excited rotation state. We collected all available photometric data from the two apparitions to reconstruct its rotation state and convex shape model. We show that light curves from 2012 and 2017 cannot be fitted with a single set of model parameters; the rotation and precession periods are significantly different for these two data sets, and they must have changed between or during the two apparitions. Nevertheless, we could fit all light curves with a dynamically self-consistent model assuming that the spin states of 2012 TC4 in 2012 and 2017 were different. To interpret our results, we developed a numerical model of its spin evolution in which we included two potentially relevant perturbations: (i) gravitational torque due to the Sun and Earth and (ii) radiation torque, known as the Yarkovsky–O’Keefe–Radzievskii–Paddack (YORP) effect. Despite our model simplicity, we found that the role of gravitational torques is negligible. Instead, we argue that the observed change of its spin state may be plausibly explained as a result of the YORP torque. To strengthen this interpretation, we verify that (i) the internal energy dissipation due to material inelasticity and (ii) an impact with a sufficiently large interplanetary particle are both highly unlikely causes of its observed spin state change. If true, this is the first case where the YORP effect has been detected for a tumbling body.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2021

Long-period Jovian Tilts the Orbits of Two sub-Neptunes Relative to Stellar Spin Axis in Kepler-129

We present the discovery of Kepler-129 d (P{sub d}=7.2{sub -0.3}{sup +0.4} yr, msini{sub d}=8.3{sub -0.7}{sup +1.1} M{sub Jup}, e{sub d}=0.15{sub -0.05}{sup +0.07}) based on six years of radial-velocity observations from Keck/HIRES. Kepler-129 also hosts two transiting sub-Neptunes: Kepler-129 b (P {sub b} = 15.79 days, r {sub b} = 2.40 ± 0.04 R {sub ⊕}) and Kepler-129 c (P {sub c} = 82.20 days, r {sub c} = 2.52 ± 0.07 R {sub ⊕}) for which we measure masses of m {sub b} < 20 M {sub ⊕} and m{sub c}=43{sub -12}{sup +13} M{sub ⊕}. Kepler-129 is a hierarchical system consisting of two tightly packed inner planets and a massive external companion. In such a system, two inner planets precess around the orbital normal of the outer companion, causing their inclinations to oscillate with time. Based on an asteroseismic analysis of Kepler data, we find tentative evidence that Kepler-129 b and c are misaligned with stellar spin axis by ≳38°, which could be torqued by Kepler-129 d if it is inclined by ≳19° relative to inner planets. Using N-body simulations, we provide additional constraints on the mutual inclination between Kepler-129 d and inner planets by estimating the fraction of time during which two inner planets both transit. The probability that two planets both transit decreases as their misalignment with Kepler-129 d increases. We also find a more massive Kepler-129 c enables the two inner planets to become strongly coupled and more resistant to perturbations from Kepler-129 d. The unusually high mass of Kepler-129 c provides a valuable benchmark for both planetary dynamics and interior structure, since the best-fit mass is consistent with this 2.5 R {sub ⊕} planet having a rocky surface.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

Chasing Shadows: Rotation of the Azimuthal Asymmetry in the TW Hya Disk

We have obtained new images of the protoplanetary disk orbiting TW Hya in visible, total intensity light with the Space Telescope Imaging Spectrograph (STIS) on the Hubble Space Telescope ( HST ), using the newly commissioned BAR5 occulter. These HST /STIS observations achieved an inner working angle of ∼0.″2, or 11.7 au, probing the system at angular radii coincident with recent images of the disk obtained by ALMA and in polarized intensity near-infrared light. By comparing our new STIS images to those taken with STIS in 2000 and with NICMOS in 1998, 2004, and 2005, we demonstrate that TW Hya’s azimuthal surface brightness asymmetry moves coherently in position angle. Between 50 au and 141 au we measure a constant angular velocity in the azimuthal brightness asymmetry of 22.°7 yr{sup −1} in a counterclockwise direction, equivalent to a period of 15.9 yr assuming circular motion. Both the (short) inferred period and lack of radial dependence of the moving shadow pattern are inconsistent with Keplerian rotation at these disk radii. We hypothesize that the asymmetry arises from the fact that the disk interior to 1 au is inclined and precessing owing to a planetary companion, thus partially shadowing the outer disk. Further monitoring of this and other shadows on protoplanetary disks potentially opens a new avenue for indirectly observing the sites of planet formation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Neutrino astrophysics in slowly rotating spacetimes permeated by nonlinear electrodynamics fields

Many theoretical and astrophysical arguments involve consideration of the effects of super strong electromagnetic fields and the rotation during the late stages of core-collapse supernovae. In what follows, we solve Einstein field equations that are minimally coupled to an arbitrary (current-free) Born–Infeld nonlinear Lagrangian L(F,G) of electrodynamics (NLED) in the slow rotation regime a ≪ r{sub +} (outer horizon size), up to first order in a/r. We cross-check the physical properties of such NLED spacetime w.r.t. against the Maxwell one. A study case on both neutrino flavor (ν{sub e}→ν{sub μ},ν{sub τ}) oscillations and flavor+helicity (spin) flip (ν{sub e}→ ν-bar {sub μ,τ}) gyroscopic precession proves that in the spacetime of a slowly rotating nonlinear charged black hole (RNCBH), the neutrino dynamics translates into a positive enhancement of the r-process (reduction of the electron fraction Y{sub e} < 0.5). Consequently, it guarantees successful hyperluminous core-collapse supernova explosions due to the enlargement of the number and amount of decaying nuclide species. This posits that, as far as the whole luminosity is concerned, hypernovae will be a proof of the formation of astrophysical RNCBH.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

The Luminous Blue Variable RMC 127 as Seen with ALMA and ATCA

We present ALMA and ATCA observations of the luminous blue variable RMC 127. The radio maps show for the first time the core of the nebula and evidence that the nebula is strongly asymmetric with a Z-pattern shape. Hints of this morphology are also visible in the archival Hubble Space Telescope Hα image, which overall resembles the radio emission. The emission mechanism in the outer nebula is optically thin free–free in the radio. At high frequencies, a component of point-source emission appears at the position of the star, up to the ALMA frequencies. The rising flux density distribution (S{sub ν}∼ν{sup 0.78±0.05}) of this object suggests thermal emission from the ionized stellar wind and indicates a departure from spherical symmetry with n{sub e}(r)∝r{sup −2}. We examine different scenarios to explain this excess of thermal emission from the wind and show that this can arise from a bipolar outflow, supporting the suggestion by other authors that the stellar wind of RMC 127 is aspherical. We fit the data with two collimated ionized wind models, and we find that the mass-loss rate can be a factor of two or more smaller than in the spherical case. We also fit the photometry obtained by IR space telescopes and deduce that the mid- to far-IR emission must arise from extended, cool (∼80 K) dust within the outer ionized nebula. Finally, we discuss two possible scenarios for the nebular morphology: the canonical single-star expanding shell geometry and a precessing jet model assuming the presence of a companion star.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Prospects of Dynamical Determination of General Relativity Parameter β and Solar Quadrupole Moment J{sub 2⊙} with Asteroid Radar Astronomy

We evaluated the prospects of quantifying the parameterized post-Newtonian parameter β and solar quadrupole moment J{sub 2⊙} with observations of near-Earth asteroids with large orbital precession rates (9 to 27 arcsec century{sup −1}). We considered existing optical and radar astrometry, as well as radar astrometry that can realistically be obtained with the Arecibo planetary radar in the next five years. Our sensitivity calculations relied on a traditional covariance analysis and Monte Carlo simulations. We found that independent estimates of β and J{sub 2⊙} can be obtained with precisions of 6 × 10{sup −4} and 3 × 10{sup −8}, respectively. Because we assumed rather conservative observational uncertainties, as is the usual practice when reporting radar astrometry, it is likely that the actual precision will be closer to 2 × 10{sup −4} and 10{sup −8}, respectively. A purely dynamical determination of solar oblateness with asteroid radar astronomy may therefore rival the helioseismology determination.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2021

A Possible Tidal Disruption Event Candidate in the Black Hole Binary System of OJ 287

The BL Lacertae OJ 287 is a supermassive black hole binary system with complex physics of its irregular flares. During 2016 October–2017 April, a surprising outburst in the X-ray, UV, and optical bands was detected, while no variability was seen in the γ-ray light curve. During the outburst, the X-ray light curves were dominated by the soft X-rays, whose peak in luminosity was ~10 46 erg s -1 —more than 10 times higher than the mean level before the outburst—and a "softer-when-brighter" phenomenon was exhibited. These above phenomena have been reported by some previous works. The hardness ratio showed negligible evolution with flare time and soft X-ray luminosity. Critically, the luminosity of the soft X-rays decayed following a power law of $t$ -5/3 , which occurs in most tidal disruption events (TDEs), and a similar trend can be seen in the UV and optical bands during the soft X-ray declining period. Helium and oxygen narrow emission lines are strengthened prominently in the optical spectra of post outburst epochs, that could be attributed to the surrounding gas caused by TDE. In conclusion, we discuss three possible origins of the event, including the jet's precession, the aftereffects of the black hole–disk impaction, and the TDE. Our results show that the TDE is the more likely scenario to explain the outburst.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2024

Jets with a Twist: The Emergence of FR0 Jets in a 3D GRMHD Simulation of Zero-angular-momentum Black Hole Accretion

Abstract Spinning supermassive black holes (BHs) in active galactic nuclei magnetically launch relativistic collimated outflows, or jets. Without angular momentum supply, such jets are thought to perish within 3 orders of magnitude in distance from the BH, well before reaching kiloparsec scales. We study the survival of such jets at the largest scale separation to date, via 3D general relativistic magnetohydrodynamic simulations of rapidly spinning BHs immersed into uniform zero-angular-momentum gas threaded by a weak vertical magnetic field. We place the gas outside the BH sphere of influence, or the Bondi radius, chosen to be much larger than the BH gravitational radius, R B = 10 3 R g . The BH develops dynamically important large-scale magnetic fields, forms a magnetically arrested disk (MAD), and launches relativistic jets that propagate well outside R B and suppress BH accretion to 1.5% of the Bondi rate, M ̇ B . Thus, low-angular-momentum accretion in the MAD state can form large-scale jets in Fanaroff–Riley (FR) type I and II galaxies. Subsequently, the disk shrinks and exits the MAD state: barely a disk (BAD), it rapidly precesses, whips the jets around, globally destroys them, and lets 5%–10% of M ̇ B reach the BH. Thereafter, the disk starts rocking back and forth by angles 90°–180°: the rocking accretion disk (RAD) launches weak intermittent jets that spread their energy over a large area and suppress BH accretion to ≲2% M ̇ B . Because the BAD and RAD states tangle up the jets and destroy them well inside R B , they are promising candidates for the more abundant, but less luminous, class of FR0 galaxies.

Astronomy & Astrophysics↗
DOE OSTI2024

The Evolution of Inclined Binary Black Holes in the Disks of Active Galactic Nuclei

The accretion disks that fuel active galactic nuclei (AGNs) may house numerous stars and compact objects, formed in situ or captured from nearby star clusters. Embedded neutron stars and black holes may form binaries and eventually merge, emitting gravitational waves detectable by LIGO/VIRGO. AGN disks are a particularly promising environment for the production of high-mass gravitational-wave events involving black holes in the pair-instability mass gap, and may facilitate electromagnetic counterparts to black hole binary mergers. However, many orders of magnitude separate the typical length scales of binary formation and those on which gravitational waves can drive binary inspirals, making binary mergers inside the disk uncertain. Previous hydrodynamical simulations of binaries have either been restricted to two dimensions entirely, or focused on binaries aligned with the midplane of the disk. Herein we present the first three-dimensional, high-resolution, local-shearing-box, inviscid hydrodynamical simulations of disk-embedded binaries over a range of orbital inclinations. We find that retrograde binaries can shrink up to 4 times as quickly as prograde binaries, and that all binaries not perfectly aligned (or anti-aligned) with the AGN disk are driven into alignment. An important consequence of this is that initially retrograde binaries will traverse the inclinations where von Zeipel–Lidov–Kozai oscillations can drive binary eccentricities to large values, potentially facilitating mergers. We also find that interactions with the AGN disk may excite eccentricities in retrograde binaries and cause the orbits of embedded binaries to precess.

79 ASTRONOMY AND ASTROPHYSICS↗