Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “Interstellar”

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.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,351 records · Page 75
All sourcesNASA NTRSDOE OSTI
DOE OSTI2013

THE ABUNDANCES OF HYDROCARBON FUNCTIONAL GROUPS IN THE INTERSTELLAR MEDIUM INFERRED FROM LABORATORY SPECTRA OF HYDROGENATED AND METHYLATED POLYCYCLIC AROMATIC HYDROCARBONS

Infrared (IR) absorption spectra of individual polycyclic aromatic hydrocarbons (PAHs) containing methyl (-CH{sub 3}), methylene (CH{sub 2}), or diamond-like CH groups and IR spectra of mixtures of methylated and hydrogenated PAHs prepared by gas-phase condensation were measured at room temperature (as grains in pellets) and at low temperature (isolated in Ne matrices). In addition, the PAH blends were subjected to an in-depth molecular structure analysis by means of high-performance liquid chromatography, nuclear magnetic resonance spectroscopy, and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. Supported by calculations at the density functional theory level, the laboratory results were applied to analyze in detail the aliphatic absorption complex of the diffuse interstellar medium at 3.4 μm and to determine the abundances of hydrocarbon functional groups. Assuming that the PAHs are mainly locked in grains, aliphatic CH {sub x} groups (x = 1, 2, 3) would contribute approximately in equal quantities to the 3.4 μm feature (N {sub CHx}/N {sub H} ≈ 10{sup –5}-2 × 10{sup –5}). The abundances, however, may be two to four times lower if a major contribution to the 3.4 μm feature comes from molecules in the gas phase. Aromatic ≅CH groups seem to be almost absent from some lines of sight, but can be nearly as abundant as each of the aliphatic components in other directions (N{sub ≅CH}/N {sub H} ∼< 2 × 10{sup –5}; upper value for grains). Due to comparatively low binding energies, astronomical IR emission sources do not display such heavy excess hydrogenation. At best, especially in protoplanetary nebulae, CH{sub 2} groups bound to aromatic molecules, i.e., excess hydrogens on the molecular periphery only, can survive the presence of a nearby star.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2018

Cosmic-ray propagation with DRAGON2: II. Nuclear interactions with the interstellar gas

Understanding the isotopic composition of cosmic rays (CRs) observed near Earth represents a milestone towards the identification of their origin. Local fluxes contain all the known stable and long-lived isotopes, reflecting the complex history of primaries and secondaries as they traverse the interstellar medium. For that reason, a numerical code which aims at describing the CR transport in the Galaxy must unavoidably rely on accurate modelling of the production of secondary particles. Here, we provide a detailed description of the nuclear cross sections and decay network as implemented in the forthcoming release of the galactic propagation code DRAGON2. We present the secondary production models implemented in the code and we apply the different prescriptions to compute quantities of interest to interpret local CR fluxes (e.g., nuclear fragmentation timescales, secondary and tertiary source terms). In particular, we develop a nuclear secondary production model aimed at accurately computing the light secondary fluxes (namely: Li, Be, B) above 1 GeV/n. This result is achieved by fitting existing empirical or semi-empirical formalisms to a large sample of measurements in the energy range 100 MeV/n to 100 GeV/n and by considering the contribution of the most relevant decaying isotopes up to iron. Concerning secondary antiparticles (positrons and antiprotons), we describe a collection of models taken from the literature, and provide a detailed quantitative comparison.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2022

Interstellar gas heating by primordial black holes

Interstellar gas heating is a powerful cosmology-independent observable for exploring the parameter space of primordial black holes (PBHs) formed in the early Universe that could constitute part of the dark matter (DM). We provide a detailed analysis of the various aspects for this observable, such as PBH emission mechanisms. Using observational data from the Leo T dwarf galaxy, we constrain the PBH abundance over a broad mass-range, M PBH ~ O(1)M ⊙ – 10 7 M ⊙ , relevant for the recently detected gravitational wave signals from intermediate-mass BHs. Here, we also consider PBH gas heating of systems with bulk relative velocity with respect to the DM, such as Galactic clouds.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Pickup Ion Effect of the Solar Wind Interaction with the Local Interstellar Medium

Pickup ions are created when interstellar neutral atoms resonantly exchange charge with the solar wind (SW) ions, especially in the supersonic part of the wind, where they carry most of the plasma pressure. Here we present numerical simulation results of the 3D heliospheric interface treating pickup ions as a separate proton fluid. To satisfy the fundamental conservation laws, we solve the system of equations describing the flow of the mixture of electrons, thermal protons, and pickup ions. To find the density and pressure of pickup ions behind the termination shock, we employ simple boundary conditions that take into account the \emph{Voyager} observations that showed that the decrease in the kinetic energy of the mixture at the termination shock predominantly contributed to the increase in the pressure of pickup ions. We show that this model adequately describes the flow of the plasma mixture and results in a noticeable decrease in the heliosheath width.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

THE DETECTION OF INTERSTELLAR ETHANIMINE (CH{sub 3}CHNH) FROM OBSERVATIONS TAKEN DURING THE GBT PRIMOS SURVEY

We have performed reaction product screening measurements using broadband rotational spectroscopy to identify rotational transition matches between laboratory spectra and the Green Bank Telescope PRIMOS radio astronomy survey spectra in Sagittarius B2 North (Sgr B2(N)). The broadband rotational spectrum of molecules created in an electrical discharge of CH{sub 3}CN and H{sub 2}S contained several frequency matches to unidentified features in the PRIMOS survey that did not have molecular assignments based on standard radio astronomy spectral catalogs. Several of these transitions are assigned to the E- and Z-isomers of ethanimine. Global fits of the rotational spectra of these isomers in the range of 8-130 GHz have been performed for both isomers using previously published mm-wave spectroscopy measurements and the microwave measurements of the current study. Possible interstellar chemistry formation routes for E-ethanimine and Z-ethanimine are discussed. The detection of ethanimine is significant because of its possible role in the formation of alanine-one of the twenty amino acids in the genetic code.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

ADVECTIVE TRANSPORT OF INTERSTELLAR PLASMA INTO THE HELIOSPHERE ACROSS THE RECONNECTING HELIOPAUSE

We discuss results of magnetohydrodynamical model simulations of plasma dynamics in the proximity of the heliopause (HP). The model is shown to fit details of the magnetic field variations observed by the Voyager 1 spacecraft during the transition from the heliosphere to the local interstellar medium (LISM). We propose an interpretation of magnetic field structures observed by Voyager 1 in terms of fine-scale physical processes. Our simulations reveal an effective transport mechanism of relatively dense LISM plasma across the reconnecting HP into the heliosphere. The mechanism is associated with annihilation of magnetic sectors in the heliospheric plasma near the HP.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2015

Magnetized interstellar molecular clouds – I. Comparison between simulations and Zeeman observations

The most accurate measurements of magnetic fields in star-forming gas are based on the Zeeman observations analysed by Crutcher et al. Here, we show that their finding that the 3D magnetic field scales approximately as density 0.65 can also be obtained from analysis of the observed line-of-sight fields. We present two large-scale adaptive-mesh-refinement magnetohydrodynamic simulations of several thousand M ⊙ of turbulent, isothermal, self-gravitating gas, one with a strong initial magnetic field (Alfven Mach number $\mathcal{M}_{A,0}=1$) and one with a weak initial field ($\mathcal{M}_{A,0}=10$). We construct samples of the 100 most massive clumps in each simulation and show that they exhibit a power-law relation between field strength and density ($\bar{n}_H$) in excellent agreement with the observed one. Our results imply that the average field in molecular clumps in the interstellar medium (ISM) is $\langle B_{tot}(\bar{n}_H)\rangle ≈ 43\bar{n}^{0.65}_{H,4}μG$. Furthermore, the median value of the ratio of the line-of-sight field to density 0.65 in the simulations is within a factor of about (1.3, 1.7) of the observed value for the strong- and weak-field cases, respectively. The median value of the mass-to-flux ratio, normalized to the critical value, is 70 per cent of the line-of-sight value. This is larger than the 50 per cent usually cited for spherical clouds because the actual mass-to-flux ratio depends on the volume-weighted field, whereas the observed one depends on the mass-weighted field. Our results indicate that the typical molecular clump in the ISM is significantly supercritical (! factor of 3). The results of our strong-field model are in very good quantitative agreement with the observations of Li et al., which show a strong correlation in field orientation between small and large scales. Because there is a negligible correlation in the weak-field model, we conclude that molecular clouds form from strongly magnetized (although magnetically supercritical) gas, in agreement with the conclusion of Li et al.

71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
DOE OSTI2017

The effect of interstellar absorption on measurements of the baryon acoustic peak in the Lyman α forest

In recent years, the autocorrelation of the hydrogen Lyman α forest has been used to observe the baryon acoustic peak at redshift 2 < z < 3.5 using tens of thousands of QSO spectra from the BOSS survey. However, the interstellar medium of the Milky Way introduces absorption lines into the spectrum of any extragalactic source. These lines, while weak and undetectable in a single BOSS spectrum, could potentially bias the cosmological signal. In order to examine this, we generate absorption line maps by stacking over a million spectra of galaxies and QSOs. Here, we find that the systematics introduced are too small to affect the current accuracy of the baryon acoustic peak, but might be relevant to future surveys such as the Dark Energy Spectroscopic Instrument (DESI). We outline a method to account for this with future data sets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2023

Gas-phase formation of the resonantly stabilized 1-indenyl (C 9 H 7 • ) radical in the interstellar medium

The 1-indenyl (C 9 H 7 • ) radical, a prototype aromatic and resonantly stabilized free radical carrying a six- and a five-membered ring, has emerged as a fundamental molecular building block of nonplanar polycyclic aromatic hydrocarbons (PAHs) and carbonaceous nanostructures in deep space and combustion systems. However, the underlying formation mechanisms have remained elusive. Here, we reveal an unconventional low-temperature gas-phase formation of 1-indenyl via barrierless ring annulation involving reactions of atomic carbon [C( 3 P)] with styrene (C 6 H 5 C 2 H 3 ) and propargyl (C 3 H 3 • ) with phenyl (C 6 H 5 • ). Macroscopic environments like molecular clouds act as natural low-temperature laboratories, where rapid molecular mass growth to 1-indenyl and subsequently complex PAHs involving vinyl side-chained aromatics and aryl radicals can occur. These reactions may account for the formation of PAHs and their derivatives in the interstellar medium and carbonaceous chondrites and could close the gap of timescales of their production and destruction in our carbonaceous universe.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Surfatron accelerator in the local interstellar cloud

Taking into account results of numerous experiments, the variability of the energy spectra of cosmic rays (protons and helium nuclei) in the energy range of 10 GeV to ~10{sup 7} GeV is explained on the basis of a hypothesis of the existence of two variable sources close to the Sun. The first (soft) surfatron source (with a size of ~100 AU) is located at the periphery of the heliosphere. The second (hard) surfatron source (with a size of ~1 pc) is situated in the Local Interstellar Cloud (LIC) at a distance of <1 pc. The constant background is described by a power-law spectrum with a slope of ~2.75. The variable heliospheric surfatron source is described by a power-law spectrum with a variable amplitude, slope, and cutoff energy, the maximum cutoff energy being in the range of E{sub CH}/Z < 1000 GeV. The variable surfatron source in the LIC is described by a power-law spectrum with a variable amplitude, slope, and cut-off energy, the maximum cut-off energy being E{sub Ð}¡{sub L}/Z ≤ 3 × 10{sup 6} GeV. The proposed model is used to approximate data from several experiments performed at close times. The energy of each cosmic-ray component is calculated. The possibility of surfatron acceleration of Fe nuclei (Z = 26) in the LIC up to an energy of E{sub CL} ~ 10{sup 17} eV and electron and positrons to the “knee” in the energy spectrum is predicted. By numerically solving a system of nonlinear equations describing the interaction between an electromagnetic wave and a charged particle with an energy of up to E/Z ~ 3 × 10{sup 6} GeV, the possibility of trapping, confinement, and acceleration of charged cosmic-ray particles by a quasi-longitudinal plasma wave is demonstrated.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

SODIUM ABSORPTION SYSTEMS TOWARD SN Ia 2014J ORIGINATE ON INTERSTELLAR SCALES

Na i D absorbing systems toward Type Ia supernovae (SNe Ia) have been intensively studied over the last decade with the aim of finding circumstellar material (CSM), which is an indirect probe of the progenitor system. However, it is difficult to deconvolve CSM components from non-variable, and often dominant, components created by interstellar material (ISM). We present a series of high-resolution spectra of SN Ia 2014J from before maximum brightness to ≳250 days after maximum brightness. The late-time spectrum provides unique information for determining the origin of the Na i D absorption systems. The deep late-time observation allows us to probe the environment around the SN at a large scale, extending to ≳40 pc. We find that a spectrum of diffuse light in the vicinity, but not directly in the line of sight, of the SN has absorbing systems nearly identical to those obtained for the “pure” SN line of sight. Therefore, basically all Na i D systems seen toward SN 2014J must originate from foreground material that extends to at least ∼40 pc in projection and none at the CSM scale. A fluctuation in the column densities at a scale of ∼20 pc is also identified. After subtracting the diffuse, “background” spectrum, the late-time Na i D profile along the SN line of sight is consistent with profiles near maximum brightness. The lack of variability on a ∼1 year timescale is consistent with the ISM interpretation for the gas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

DYNAMIC SPECTRAL MAPPING OF INTERSTELLAR PLASMA LENSES

Compact radio sources sometimes exhibit intervals of large, rapid changes in their flux density, due to lensing by interstellar plasma crossing the line of sight. A novel survey program has made it possible to discover these “Extreme Scattering Events” (ESEs) in real time, resulting in a high-quality dynamic spectrum of an ESE observed in PKS 1939–315. Here we present a method for determining the column-density profile of a plasma lens, given only the dynamic radio spectrum of the lensed source, under the assumption that the lens is either axisymmetric or totally anisotropic. Our technique relies on the known, strong frequency dependence of the plasma refractive index in order to determine how points in the dynamic spectrum map to positions on the lens. We apply our method to high-frequency (4.2–10.8 GHz) data from the Australia Telescope Compact Array of the PKS 1939–315 ESE. The derived electron column-density profiles are very similar for the two geometries we consider, and both yield a good visual match to the data. However, the fit residuals are substantially above the noise level, and deficiencies are evident when we compare the predictions of our model to lower-frequency (1.6–3.1 GHz) data on the same ESE, thus motivating future development of more sophisticated inversion techniques.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

RADIO SYNCHROTRON FLUCTUATION STATISTICS AS A PROBE OF MAGNETIZED INTERSTELLAR TURBULENCE

We investigate how observations of synchrotron intensity fluctuations can be used to probe the sonic and Alfvénic Mach numbers of interstellar turbulence, based on mock observations performed on simulations of magnetohydrodynamic turbulence. We find that the structure function slope and a diagnostic of anisotropy that we call the integrated quadrupole ratio modulus both depend on the Alfvénic Mach number. However, these statistics also depend on the orientation of the mean magnetic field in the synchrotron emitting region relative to our line of sight, and this creates a degeneracy that cannot be broken by observations of synchrotron intensity alone. We conclude that the polarization of synchrotron emission could be analyzed to break this degeneracy, and suggest that this will be possible with the Square Kilometre Array.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

VOYAGER OBSERVATIONS OF MAGNETIC WAVES DUE TO NEWBORN INTERSTELLAR PICKUP IONS: 2–6 au

We report observations by the Voyager 1 and 2 spacecraft of low-frequency magnetic waves excited by newborn interstellar pickup ions H{sup +} and He{sup +} during 1978–1979 when the spacecraft were in the range from 2 to 6.3 au. The waves have the expected association with the cyclotron frequency of the source ions, are left-hand polarized in the spacecraft frame, and have minimum variance directions that are quasi-parallel to the local mean magnetic field. There is one exception to this in that one wave event that is excited by pickup H{sup +} is right-hand polarized in the spacecraft frame, but similar exceptions have been reported by Cannon et al. and remain unexplained. We apply the theory of Lee and Ip that predicts the energy spectrum of the waves and then compare growth rates with turbulent cascade rates under the assumption that turbulence acts to destroy the enhanced wave activity and transport the associated energy to smaller scales where dissipation heats the background plasma. As with Cannon et al., we find that the ability to observe the waves depends on the ambient turbulence being weak when compared with growth rates, thereby allowing sustained wave growth. This analysis implies that the coupled processes of pitch-angle scattering and wave generation are continuously associated with newly ionized pickup ions, despite the fact that the waves themselves may not be directly observable. When waves are not observed, but wave excitation can be argued to be present, the wave energy is simply absorbed by the turbulence at a rate that prevents significant accumulation. In this way, the kinetic process of wave excitation by scattering of newborn ions continues to heat the plasma without producing observable wave energy. These findings support theoretical models that invoke efficient scattering of new pickup ions, leading to turbulent driving in the outer solar wind and in the IBEX ribbon beyond the heliopause.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

CHEMICAL SIMULATIONS OF PREBIOTIC MOLECULES: INTERSTELLAR ETHANIMINE ISOMERS

The E- and Z- isomers of ethanimine (CH{sub 3}CHNH) were recently detected toward the star-forming region Sagittarius (Sgr) B2(N) using the Green Bank Telescope PRIMOS cm-wave spectral data, and imaged by the Australia Telescope Compact Array. Ethanimine is not reported in the hot cores of Sgr B2, but only in gas that absorbs at +64 and +82 km s{sup −1} in the foreground of continuum emission generated by H ii regions. The ethanimine isomers can serve as precursors of the amino acid alanine and may play important roles in forming biological molecules in the interstellar medium. Here we present a study of the chemistry of ethanimine using a gas-grain simulation based on rate equations, with both isothermal and warm-up conditions. In addition, the density, kinetic temperature, and cosmic ray ionization rate have been varied. For a variety of physical conditions in the warm-up models for Sgr B2(N) and environs, the simulations show reasonable agreement with observationally obtained abundances. Isothermal models of translucent clouds along the same line of sight yield much lower abundances, so that ethanimine would be much more difficult to detect in these sources despite the fact that other complex molecules have been detected there.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

INTERSTELLAR PICKUP ION ACCELERATION IN THE TURBULENT MAGNETIC FIELD AT THE SOLAR WIND TERMINATION SHOCK USING A FOCUSED TRANSPORT APPROACH

We study the physics of locally born interstellar pickup proton acceleration at the nearly perpendicular solar wind termination shock (SWTS) in the presence of a random magnetic field spiral angle using a focused transport model. Guided by Voyager 2 observations, the spiral angle is modeled with a q -Gaussian distribution. The spiral angle fluctuations, which are used to generate the perpendicular diffusion of pickup protons across the SWTS, play a key role in enabling efficient injection and rapid diffusive shock acceleration (DSA) when these particles follow field lines. Our simulations suggest that variation of both the shape ( q -value) and the standard deviation ( σ -value) of the q -Gaussian distribution significantly affect the injection speed, pitch-angle anisotropy, radial distribution, and the efficiency of the DSA of pickup protons at the SWTS. For example, increasing q and especially reducing σ enhances the DSA rate.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2016

Insights into hydrocarbon chain and aromatic ring formation in the interstellar medium: computational study of the isomers of C{sub 4}H{sub 3}{sup +} C{sub 6}H{sub 3}{sup +} and C{sub 6}H{sub 5}{sup +} and their formation pathways

Small hydrocarbons such as acetylene is present in circumstellar envelopes of carbon-rich stars, but the processes that yield larger molecules, and eventually polycyclic aromatic hydrocarbons (PAHs), remain poorly understood. To gain additional insight into the early steps of such processes, electronic structure calculations were performed on the potential energy surfaces of C{sub 4}H{sub 3}{sup +}, C{sub 6}H{sub 3}{sup +} and C{sub 6}H{sub 5}{sup +}. The results establish reactive pathways from acetylene and its ion to formation of the first aromatic ring. We characterize the stable isomers, their spectroscopic properties, and many of the transition structures that represent barriers to isomerization. The pathways to stabilized C{sub 4}H{sub 3}{sup +} and C{sub 6}H{sub 3}{sup +} are most likely to arise from unimolecular decomposition of hot C{sub 4}H{sub 4}{sup +} and C{sub 6}H{sub 4}{sup +} by H atom elimination. By contrast, we found an ion-molecule pathway to C{sub 6}H{sub 5}{sup +} to be very stable to fragmentation and elimination reactions even without collisional stabilization. This aromatic species is a good nucleation center for the growth of larger PAHs in interstellar conditions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2016

LATITUDE, ENERGY, AND TIME VARIATIONS IN THE ENERGETIC NEUTRAL ATOM SPECTRAL INDICES MEASURED BY THE INTERSTELLAR BOUNDARY EXPLORER ( IBEX )

We investigate the latitude, energy, and temporal variations of the ∼0.5–6 keV energetic neutral atom (ENA) fluxes and spectral indices measured by the Interstellar Boundary Explorer ( IBEX ) outside of the Ribbon from 2009 to 2013. By combining all-sky maps for years 1–3 and years 4–5, we find that the >1.2 keV globally distributed (GD) ENA fluxes at all latitudes decrease by ∼25% from years 1–3 to years 4–5, but there is no change (<5%) in the corresponding spectral indices. We also show that the latitudinal profile and energy-dependence of the ≥1 keV ENA spectral indices outside the Ribbon exhibit no significant time differences between years 1–3 and 4–5, lending strong support for the notion that the highly organized, persistent energy dependence and latitudinal pattern of the ENA spectral indices during 2009–2014 are determined by that of the solar wind (SW) speed observed in the inner heliosphere during the deep solar minimum conditions of 2006–2010. In contrast, the ∼25% decrease in the >1.2 keV ENA fluxes at all latitudes from years 1–3 to years 4–5 occurs because the magnitude of the driving SW parameters (SW density or dynamic pressure) diminished significantly from 2006 to 2010. Based on the reconstructed latitudinal and temporal profiles of SW parameters from 2011 to 2014, i.e., during the rising phase of solar cycle 24, we suggest that the GD ENA fluxes in years 2014–2017, i.e., in maps 6–9, will either stabilize or increase and the latitudinal pattern and energy dependence of the corresponding spectral indices will be disrupted.

79 ASTRONOMY AND ASTROPHYSICS↗