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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
DOE OSTI2017

Discovery of Molecular and Atomic Clouds Associated with the Magellanic Superbubble 30 Doradus C

We analyzed the 2.6 mm CO and 21 cm H i lines toward the Magellanic superbubble 30 Doradus C, in order to reveal the associated molecular and atomic gas. We uncovered five molecular clouds in a velocity range from 251 to 276 km s{sup −1} toward the western shell. The non-thermal X-rays are clearly enhanced around the molecular clouds on a parsec scale, suggesting possible evidence for magnetic field amplification via shock–cloud interaction. The thermal X-rays are brighter in the eastern shell, where there are no dense molecular or atomic clouds, opposite to the western shell. The TeV γ-ray distribution may spatially match the total interstellar proton column density as well as the non-thermal X-rays. If the hadronic γ-ray is dominant, the total energy of the cosmic-ray protons is at least ∼1.2×10{sup 50} erg with the estimated mean interstellar proton density ∼60 cm{sup −3}. In addition, the γ-ray flux associated with the molecular cloud (e.g., MC3) could be detected and resolved by the Cherenkov Telescope Array (CTA). This should permit CTA to probe the diffusion of cosmic-rays into the associated dense ISM.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

A Simple and Accurate Network for Hydrogen and Carbon Chemistry in the Interstellar Medium

Chemistry plays an important role in the interstellar medium (ISM), regulating the heating and cooling of the gas and determining abundances of molecular species that trace gas properties in observations. Although solving the time-dependent equations is necessary for accurate abundances and temperature in the dynamic ISM, a full chemical network is too computationally expensive to incorporate into numerical simulations. In this paper, we propose a new simplified chemical network for hydrogen and carbon chemistry in the atomic and molecular ISM. We compare results from our chemical network in detail with results from a full photodissociation region (PDR) code, and also with the Nelson and Langer (NL99) network previously adopted in the simulation literature. We show that our chemical network gives similar results to the PDR code in the equilibrium abundances of all species over a wide range of densities, temperature, and metallicities, whereas the NL99 network shows significant disagreement. Applying our network to 1D models, we find that the CO-dominated regime delimits the coldest gas and that the corresponding temperature tracks the cosmic-ray ionization rate in molecular clouds. We provide a simple fit for the locus of CO-dominated regions as a function of gas density and column. We also compare with observations of diffuse and translucent clouds. We find that the CO, CH{sub x}, and OH{sub x} abundances are consistent with equilibrium predictions for densities n=100--1000 cm{sup −3}, but the predicted equilibrium C abundance is higher than that seen in observations, signaling the potential importance of non-equilibrium/dynamical effects.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Formation of Methylamine and Ethylamine in Extraterrestrial Ices and Their Role as Fundamental Building Blocks of Proteinogenic α -amino Acids

The –CH–NH{sub 2} moiety represents the fundamental building block of all proteinogenic amino acids, with the cyclic amino acid proline being a special case (–CH–NH– in proline). Exploiting a chemical retrosynthesis, we reveal that methylamine (CH{sub 3}NH{sub 2}) and/or ethylamine (CH{sub 3}CH{sub 2}NH{sub 2}) are essential precursors in the formation of each proteinogenic amino acid. In the present study we elucidate the abiotic formation of methylamine and ethylamine from ammonia (NH{sub 3}) and methane (CH{sub 4}) ices exposed to secondary electrons generated by energetic cosmic radiation in cometary and interstellar model ices. Our experiments show that methylamine and ethylamine are crucial reaction products in irradiated ices composed of ammonia and methane. Using isotopic substitution studies we further obtain valuable information on the specific reaction pathways toward methylamine. The very recent identification of methylamine and ethylamine together with glycine in the coma of 67P/Churyumov–Gerasimenko underlines their potential to the extraterrestrial formation of amino acids.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

NuSTAR Hard X-Ray Observation of the Gamma-Ray Binary Candidate HESS J1832–093

We present a hard X-ray observation of the TeV gamma-ray binary candidate HESS J1832−093, which is coincident with the supernova remnant G22.7−0.2, using the Nuclear Spectroscopic Telescope Array. Non-thermal X-ray emission from XMMU J183245−0921539, the X-ray source associated with HESS J1832−093, is detected up to ∼30 keV and is well-described by an absorbed power-law model with a best-fit photon index Γ=1.5±0.1. A re-analysis of archival Chandra and XMM-Newton data finds that the long-term X-ray flux increase of XMMU J183245−0921539 is 50{sub −20}{sup +40}% (90% C.L.), much less than previously reported. A search for a pulsar spin period or binary orbit modulation yields no significant signal to a pulse fraction limit of f{sub p}<19% in the range 4 ms < P<40 ks. No red noise is detected in the FFT power spectrum to suggest active accretion from a binary system. While further evidence is required, we argue that the X-ray and gamma-ray properties of XMMU J183245−0921539 are most consistent with a non-accreting binary generating synchrotron X-rays from particle acceleration in the shock formed as a result of the pulsar and stellar wind collision. We also report on three nearby hard X-ray sources, one of which may be associated with diffuse emission from a fast-moving supernova fragment interacting with a dense molecular cloud.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

ADIABATIC HEATING OF CONTRACTING TURBULENT FLUIDS

Turbulence influences the behavior of many astrophysical systems, frequently by providing non-thermal pressure support through random bulk motions. Although turbulence is commonly studied in systems with constant volume and mean density, turbulent astrophysical gases often expand or contract under the influence of pressure or gravity. Here, we examine the behavior of turbulence in contracting volumes using idealized models of compressed gases. Employing numerical simulations and an analytical model, we identify a simple mechanism by which the turbulent motions of contracting gases 'adiabatically heat', experiencing an increase in their random bulk velocities until the largest eddies in the gas circulate over a Hubble time of the contraction. Adiabatic heating provides a mechanism for sustaining turbulence in gases where no large-scale driving exists. We describe this mechanism in detail and discuss some potential applications to turbulence in astrophysical settings.

79 ASTRONOMY AND ASTROPHYSICS↗
NASA NTRS1979

Predicted versus observed cosmic-ray-produced noble gases in lunar samples - Improved Kr production ratios

New sets of cross sections for the production of krypton isotopes from targets of Rb, Sr, Y, and Zr have been constructed primarily on the bases of experimental excitation functions for Kr production from Y. These cross sections were used to calculate galactic-cosmic-ray and solar-proton production rates for Kr isotopes in the moon. The paper reports spallation Kr data obtained from ilmenite separates of rocks 10017 and 10047. Production rates and isotopic ratios for cosmogenic Kr observed in ten well-documented lunar samples and in ilmenite separates and bulk samples from several lunar rocks with long but unknown irradiation histories were compared with predicted rates and ratios. The agreements were generally quite good.

Regnier, S.↗
DOE OSTI2016

A hot gaseous galaxy halo candidate with Mg X absorption

The hot gas in galaxy halos may account for a significant fraction of missing baryons in galaxies, and some of these gases can be traced by high ionization absorption systems in QSO UV spectra. Using high S/N Hubble Space Telescope/Cosmic Origins Spectrograph spectra, we discovered a high ionization state system at z = 1.1912 in the sightline toward LBQS 1435-0134, and two-component absorption lines are matched for Mg x, Ne viii, Ne vi, O vi, Ne v, O v, Ne iv, O iv, N iv, O iii, and H i. Mg x, detected for the first time (5.8σ), is a particularly direct tracer of hot galactic halos, as its peak ion fraction occurs near 10{sup 6.1} K, about the temperature of a virialized hot galaxy halo of mass ∼0.5M{sup ∗}. With Mg x and Ne viii, a photoionization model cannot reproduce the observed column densities with path lengths of galaxy halos. For collisional ionization models, one or two-temperature models do not produce acceptable fits, but a three-temperature model or a power-law model can produce the observed results. In the power-law model, dN/dT=10{sup 4.4±2.2−[Z/X]}T{sup 1.55±0.41} with temperatures in the range of 10{sup 4.39±0.13} K<T<10{sup 6.04±0.05} K, the total hydrogen column density is 8.2×10{sup 19}(0.3 Z{sub ⊙}/Z) cm{sup −2} and the positive power-law index indicates most of the mass is at the high temperature end. We suggest that this absorption system is a hot volume-filled galaxy halo rather than interaction layers between the hot halo and cool clouds. The temperature dependence of the column density is likely due to the local mixture of multiple phase gases.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2011

DETECTION OF OUTFLOWING AND EXTRAPLANAR GAS IN DISKS IN AN ASSEMBLING GALAXY CLUSTER AT z = 0.37

We detect ionized gas characteristics indicative of winds in three disk-dominated galaxies that are members of a super-group at z = 0.37 that will merge to form a Coma-mass cluster. All three galaxies are IR luminous (L{sub IR} > 4 Multiplication-Sign 10{sup 10} L{sub Sun }, SFR > 8 M{sub Sun} yr{sup -1}) and lie outside the X-ray cores of the galaxy groups. We find that the most IR-luminous galaxy has strong blueshifted and redshifted emission lines with velocities of {approx} {+-} 200 km s{sup -1} and a third, blueshifted ({approx}900 km s{sup -1}) component. This galaxy's line widths (H{beta}, [O III]{lambda}5007, [N II], H{alpha}) correspond to velocities of 100-1000 km s{sup -1}. We detect extraplanar gas in two of the three galaxies with SFR >8 M{sub Sun} yr{sup -1} whose orientations are approximately edge-on and which have integral field unit (IFU) spaxels off the stellar disk. IFU maps reveal that the extraplanar gas extends to r{sub h} {approx} 10 kpc; [N II] and H{alpha} line widths correspond to velocities of {approx}200-400 km s{sup -1} in the disk and decrease to {approx}50-150 km s{sup -1} above the disk. Multi-wavelength observations indicate that the emission is dominated by star formation. Including the most IR-luminous galaxy we find that 18% of supergroup members with SFR >8 M{sub Sun} yr{sup -1} show ionized gas characteristics indicative of outflows. This is a lower limit as showing that gas is outflowing in the remaining, moderately inclined, galaxies requires a non-trivial decoupling of contributions to the emission lines from rotational and turbulent motion. Ionized gas mass loss in these winds is {approx}0.1 M{sub Sun} yr{sup -1} for each galaxy, although the winds are likely to entrain significantly larger amounts of mass in neutral and molecular gases.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Ultraviolet and Optical Emission Line Outflows in the Heavily Obscured Quasar SDSS J000610.67+121501.2: At the Scale of the Dusty Torus and Beyond

Broad emission line outflows of active galactic nuclei have been proposed for many years but are very difficult to quantitatively study because of the coexistence of the gravitationally bound and outflow emission. We present detailed analysis of a heavily reddened quasar, SDSS J000610.67+121501.2, whose normal ultraviolet broad emission lines (BELs) are heavily suppressed by the dusty torus as a natural “coronagraph,” and thus the blueshifted BELs (BBELs) can be reliably measured. The physical properties of the emission-line outflows are derived as follows: ionization parameter U∼10{sup −0.5}, column density N{sub H}∼10{sup 22.0} cm{sup −2}, covering fraction of ∼0.1, and upper limit density of n{sub H}∼10{sup 5.8} cm{sup −3}. The outflow gases are located at least 41 pc away from the central engine, which suggests that they have expanded to the scale of the dust torus or beyond. Besides, Lyα shows a narrow symmetric component, to our surprise, which is undetected in any other lines. After inspecting the narrow emission line region and the star-forming region as the origin of the Lyα narrow line, we propose that the end result of outflows, diffusing gases in the larger region, acts as the screen of Lyα photons. Future high spatial resolution spectrometry and/or spectropolarimetric observations are needed to make a final clarification.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Redox States of Initial Atmospheres Outgassed on Rocky Planets and Planetesimals

The Earth and other rocky planets and planetesimals in the solar system formed through the mixing of materials from various radial locations in the solar nebula. This primordial material likely had a range of oxidation states as well as bulk compositions and volatile abundances. We investigate the oxygen fugacity produced by the outgassing of mixtures of solid meteoritic material, which approximate the primitive nebular materials. We find that the gas composition and oxygen fugacity of binary and ternary mixtures of meteoritic materials vary depending on the proportion of reduced versus oxidized material, and also find that mixtures using differentiated materials do not show the same oxygen fugacity trends as those using similarly reduced but undifferentiated materials. We also find that simply mixing the gases produced by individual meteoritic materials together does not correctly reproduce the gas composition or oxygen fugacity of the binary and ternary mixtures. We provide tabulated fits for the oxygen fugacities of all of the individual materials and binary mixtures that we investigate. These values may be useful in planetary formation models, models of volatile transport on planetesimals or meteorite parent bodies, or models of trace element partitioning during metal-silicate fractionation.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2012

VAPORIZATION OF THE EARTH: APPLICATION TO EXOPLANET ATMOSPHERES

Currently, there are about three dozen known super-Earths (M < 10 M{sub Circled-Plus }), of which eight are transiting planets suitable for atmospheric follow-up observations. Some of the planets are exposed to extreme temperatures as they orbit close to their host stars, e.g., CoRot-7b, and all of these planets have equilibrium temperatures significantly hotter than the Earth. Such planets can develop atmospheres through (partial) vaporization of their crustal and/or mantle silicates. We investigated the chemical equilibrium composition of such heated systems from 500 to 4000 K and total pressures from 10{sup -6} to 10{sup +2} bars. The major gases are H{sub 2}O and CO{sub 2} over broad temperature and pressure ranges, and Na, K, O{sub 2}, SiO, and O at high temperatures and low pressures. We discuss the differences in atmospheric composition arising from vaporization of SiO{sub 2}-rich (i.e., felsic) silicates (like Earth's continental crust) and MgO-, FeO-rich (i.e., mafic) silicates (like the bulk silicate Earth). The computational results will be useful in planning spectroscopic studies of the atmospheres of Earth-like exoplanets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Experimental and numerical investigation of reactive shock-accelerated flows

The main goal of this program was to establish a qualitative and quantitative connection, based on the appropriate dimensionless parameters and scaling laws, between shock-induced distortion of astrophysical plasma density clumps and their earthbound analog in a shock tube. These objectives were pursued by carrying out laboratory experiments and numerical simulations to study the evolution of two gas bubbles accelerated by planar shock waves and compare the results to available astrophysical observations. The experiments were carried out in an vertical, downward-firing shock tube, 9.2 m long, with square internal cross section (25×25 cm 2 ). Specific goals were to quantify the effect of the shock strength (Mach number, M) and the density contrast between the bubble gas and its surroundings (usually quantified by the Atwood number, i.e. the dimensionless density difference between the two gases) upon some of the most important flow features (e.g. macroscopic properties; turbulence and mixing rates). The computational component of the work performed through this program was aimed at (a) studying the physics of multi-phase compressible flows in the context of astrophysics plasmas and (b) providing a computational connection between laboratory experiments and the astrophysical application of shock-bubble interactions. Throughout the study, we used the FLASH4.2 code to run hydrodynamical and magnetohydrodynamical simulations of shock bubble interactions on an adaptive mesh.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Strong Lyα emission in the proximate damped LYα absorption trough toward the quasar SDSS J095253.83+011422.0

SDSS J095253.83+011422.0 (J0952+0114) was reported by Hall et al. as an exotic quasar at z{sub em} = 3.020. In contrast to prominent broad metal-line emission with FWHM ∼ 9000 km s{sup −1}, only a narrow Lyα emission line is present with FWHM ∼ 1000 km s{sup −1}. The absence of a broad Lyα emission line has been a mystery for more than a decade. In this paper, we demonstrate that this absence is due to dark proximate damped Lyα absorption (PDLA) at z{sub abs} = 3.010 by identifying associated Lyman absorption line series from the damped Lyβ up to Ly9, as well as the Lyman limit absorption edge. The PDLA cloud has a column density of logN{sub HI}(cm{sup −2})=21.8±0.2, a metallicity of [Zn/H] > −1.0, and a spatial extent exceeding the narrow emission line region (NELR) of the quasar. With a luminosity of L{sub Lyα}∼10{sup 45} erg s{sup −1}, the residual Lyα emission superposed on the PDLA trough is two orders of magnitude stronger than found by previous reports. This is best explained as re-radiated photons arising from the quasar outflowing gas on a larger scale than in the NELR. The PDLA here, acting like a natural coronagraph, provides us with valuable insight into the illuminated gases in the vicinity of the quasar, which are usually hard to resolve due to their small size and the “seeing fuzz” of bright quasars. Notably, J0952+0114 analogs might be easily omitted in the spectroscopic surveys of DLAs and PDLAs because their damped Lyα troughs can be fully filled by additional strong Lyα emissions. Our preliminary survey shows that such systems are not very rare. They could potentially be a unique sample for probing strong quasar feedback phenomena in the early universe.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

CLOUDS IN SUPER-EARTH ATMOSPHERES: CHEMICAL EQUILIBRIUM CALCULATIONS

Recent studies have unequivocally proven the existence of clouds in super-Earth atmospheres. Here we provide a theoretical context for the formation of super-Earth clouds by determining which condensates are likely to form under the assumption of chemical equilibrium. We study super-Earth atmospheres of diverse bulk composition, which are assumed to form by outgassing from a solid core of chondritic material, following Schaefer and Fegley. The super-Earth atmospheres that we study arise from planetary cores made up of individual types of chondritic meteorites. They range from highly reducing to oxidizing and have carbon to oxygen (C:O) ratios that are both sub-solar and super-solar, thereby spanning a range of atmospheric composition that is appropriate for low-mass exoplanets. Given the atomic makeup of these atmospheres, we minimize the global Gibbs free energy of formation for over 550 gases and condensates to obtain the molecular composition of the atmospheres over a temperature range of 350–3000 K. Clouds should form along the temperature–pressure boundaries where the condensed species appear in our calculation. We find that the composition of condensate clouds depends strongly on both the H:O and C:O ratios. For the super-Earth archetype GJ 1214b, KCl and ZnS are the primary cloud-forming condensates at solar composition, in agreement with previous work. However, for oxidizing atmospheres, K{sub 2}SO{sub 4} and ZnO condensates are favored instead, and for carbon-rich atmospheres with super-solar C:O ratios, graphite clouds appear. For even hotter planets, clouds form from a wide variety of rock-forming and metallic species.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Oscillator strength measurement for the A(0–6)–X(0), C(0)–X(0), and E(0)–X(0) transitions of CO by the dipole (γ, γ) method

The oscillator strengths of CO, especially for the excitations to the predissociating levels C{sup 1}Σ{sup +} and E{sup 1}Π, have significant applications in the studies of interstellar gases. A large number of investigations, applying a variety of experimental and calculational methods, have focused on the determination of these oscillator strengths. However, deviations of more than 10% have been observed, even for the same experimental method. In this case, we introduce a new technique, the dipole (γ, γ), to measure the oscillator strengths. The obtained oscillator strengths of the strong bands C{sup 1}Σ{sup +}(ν{sup ′}=0)−X{sup 1}Σ{sup +} and E{sup 1}Π(ν{sup ′}=0)−X{sup 1}Σ{sup +} in this work reach high accuracy and are in excellent agreement with some previous results, although they are different from the recommended values in other works. In addition, we measured the oscillator strengths of the A{sup 1}Π(ν{sup ′}=0−6)−X{sup 1}Σ{sup +} bands, and the electronic transition moment dependence on r-centroid was derived.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

FINDING EXTRATERRESTRIAL LIFE USING GROUND-BASED HIGH-DISPERSION SPECTROSCOPY

Exoplanet observations promise one day to unveil the presence of extraterrestrial life. Atmospheric compounds in strong chemical disequilibrium would point to large-scale biological activity just as oxygen and methane do in the Earth's atmosphere. The cancellation of both the Terrestrial Planet Finder and Darwin missions means that it is unlikely that a dedicated space telescope to search for biomarker gases in exoplanet atmospheres will be launched within the next 25 years. Here we show that ground-based telescopes provide a strong alternative for finding biomarkers in exoplanet atmospheres through transit observations. Recent results on hot Jupiters show the enormous potential of high-dispersion spectroscopy to separate the extraterrestrial and telluric signals, making use of the Doppler shift of the planet. The transmission signal of oxygen from an Earth-twin orbiting a small red dwarf star is only a factor of three smaller than that of carbon monoxide recently detected in the hot Jupiter {tau} Booetis b, albeit such a star will be orders of magnitude fainter. We show that if Earth-like planets are common, the planned extremely large telescopes can detect oxygen within a few dozen transits. Ultimately, large arrays of dedicated flux-collector telescopes equipped with high-dispersion spectrographs can provide the large collecting area needed to perform a statistical study of life-bearing planets in the solar neighborhood.

79 ASTRONOMY AND ASTROPHYSICS↗