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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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NASA NTRS1988

A model for the interaction between stars and gas in the interstellar medium

A model for the ISM is considered in which stars lose mass and heat the gas while the gas can form into stars. Three scale-free models are calculated, and in each case the star formation instability leads to a network of dense filaments that surround hotter, more rarefied gas, all of which are close to pressure equilibrium. Depending upon the star formation and cooling laws adopted, the stars are located either in the middle of a bubble or along the inside edge of a dense filament. When a model for the ISM with a cooling curve appropriate for gas of cosmic abundance and a star formation rate proportional to the local gas density is used, the star formation instability is found to grow at temperatures below about 10,000 K. A network structure develops in which most of the mass is in neutral filaments. Newly formed stars lie adjacent to the filaments and create pressure forces that lead to filament motion.

Chiang, Wei-Hwan↗
NASA NTRS1995

Electron density power spectrum in the local interstellar medium

Interstellar scintillation (ISS), fluctuations in the amplitude and phase of radio waves caused by scattering in the interstellar medium, is important as a diagnostic of interstellar plasma turbulence. ISS is also of interest because it is noise for other radio astronomical observations. The unifying concern is the power spectrum of the interstellar electron density. Here we use ISS observations through the nearby (less than or approximately =1 kpc) (ISM) to estimate the spectrum. From measurements of angular broadening of pulsars and extragalactic sources, decorrelation bandwidth of pulsars, refractive steering of features in pulsar dynamic spectra, dispersion measured fluctuations of pulsars, and refractive scintillation index measurements, we construct a composite structure function that is approximately power law over 2 x 10(exp 6) m less than scale less than 10(exp 13) m. The data are consistent with the structure function having a logarithmic slope versus baseline less than 2; thus there is a meaningful connection between scales in the radiowave fluctuation field and the scales in the electron density field causing the scattering. The data give an upper limit to the inner scale, l(sub o) less than or approximately 10(exp 8) m and are consistent with much smaller values. We construct a composite electron density spectrum that is approximately power law over at least the approximately = 5 decade wavenumber range 10(exp -13)/m less than wavenumber less than 10(exp -8)/m and that may extend to higher wavenumbers. The average spectral index of electron density over this wavenumber range is approximately = 3.7, very close to the value expected for a Kolmogorov process. The outer scale size, L(sub o), must be greater than or approximately = 10(exp 13) m (determined from dispersion measure fluctuations). When the ISS data are combined with measurements of differential Faraday rotation angle, and gradients in the average electron density, constraints can be put on the spectrum at much smaller wave numbers. The composite spectrum is consistent with a Kolmogorov-like power law over a huge range (10 or more decades) of spatial wavenumber with an infrared outer scale L(sub o) greater than or approximately 10(exp 18)m. This power-law subrange-expressed as ratio of outer to inner scales-is comparable to or larger than that of other naturally occurring turbulent fluids, such as the oceans or the solar wind. We outline some of the theories for generating and maintaining such a spectrum over this huge wavenumber range.

Armstrong, J. W.↗
NASA NTRS2000

Deconstructing the Spectrum of the Soft X-ray Background

The soft X-ray background in the 0.1-1.0 keV band is known to be produced by at least three sources; the Local Hot Bubble (LHB), the extragalactic power law (EPL), and a seemingly galactic component that lies outside the bulk of the absorption that is due to the ISM of the galactic disk. This last component, which we call the Trans-Absorption Emission (TAE), has been modeled by a number of groups who have derived disparate measures of its temperature. The differences have arisen from differing assumptions about the structure of the emitting gas and unrecognized methodological difficulties. In particular, spectral fitting methods do not uniquely separate the TAE from the foreground emission that is due the LHB. This "degeneracy" can be resolved using the angular variation of the absorption of the TAE. We show that the TAE cannot be characterized by a single thermal component; no single-component model can be consistent with both the spectral energy distribution of the TAE emission and the angular variation due to absorption by the galactic disk. We use the angular anticorrelation of the ROSAT All-Sky Survey with the galactic absorption to separate local from distant emission components, and to fit the spectral energy distribution of the resulting distant emission. We find that the emission is best described by a two-thermal-component model with logT(sub S) = 6.06(sup +0.14, sub -0.12) and log T(sub H) = 6.42(sup +0.14, sub -0.12). This two-thermal-component TAE fits the ROSAT spectral energy distribution significantly better than single-component models, and is consistent with both angular variation and spectral constraints.

Kuntz, K. D.↗
NASA NTRS2003

High-Velocity Absorption Features in FUSE Spectra of Eta Carinae

Numerous broad (200 to 1000 km/sec) features in the FUSE spectrum (905-1187 A) of eta Carinae are identified as absorption by a forest of high-velocity narrow lines formed in the expanding circumstellar envelope. These features were previously thought to be P-Cygni lines arising in the wind of the central star. The features span a heliocentric velocity range of -140 to -580 km/sec and are seen prominently in low-ionization ground-state transitions (e.g. N I 1134-35, Fe II 1145-42, 1133, 1127- 22, P II 1153, C I 1158) in addition to C III] 1176 A. The high-velocity components of the FUSE transitions have depths about 50% below the continuum. The identifications are consistent with the complex velocity structures seen in ground- and excited-state transitions of Mg I, Mg 11, Fe II, V II, etc observed in STIS/E230H spectra. The origin of other broad features of similar width and depth in the FUSE spectrum, but without low-velocity ISM absorption, are unidentified. However, they are suspected of being absorption of singly-ionized iron-peak elements (e.g. Fe II, V II, Cr II) out of excited levels 1,000 to 20,000 cmE-l above the ground state. The high-velocity features seen in Fe II 1145 are also present in Fe II 1608 (STIS/E140M), but are highly saturated in the latter. Since these transitions have nearly identical log (flambda) (1.998 vs. 2.080), the differences in the profiles are attributable to the different aperture sizes used (30 x 30 arcsec for FUSE, 0.2 x 0.2 arcsec for STIS/E140M). The high-velocity gas appears to be very patchy or has a small covering factor near the central star. Eta Carinae has been observed several times by FUSE over the past three years. The FUSE flux levels and spectral features in eta Car are essentially unchanged over the 2000 March to June 2002 period, establishing a baseline far-UV spectrum in advance of the predicted spectroscopic minimum in 2003.

Sonneborn, G.↗
NASA NTRS1993

The dynamic interstellar medium in NGC 4438

We present multiwavelength observations of the interstellar medium in the disturbed galaxy NGC 4438. We find extended emission-line filaments, which are kinematically unrelated to the galaxy disk. For one of these features, an extended loop, we propose a scheme in which the 'bubble' seen at radio wavelengths has swept a clear path for outflowing material from the nucleus to ionize more distant material. Another radial emission-line feature might represent shocks in the disk along a gravitationally-defined caustic produced during a tidal encounter, or a 'searchlight beam' escaping the inner dusty regions of the galaxy. Energy-balance arguments favor the shock picture, but further study will be important in understanding this feature. Emission-line ratios indicate that shocks may be important in the energetics of the interstellar medium (ISM) through much of the disk of NGC 4438; the alternative is star formation in a uniformly very dense ISM. We use K-band data to locate the stellar peak of the galaxy, which is just outside the prominent radio-continuum loop or shell feature. The nucleus itself is at most a very weak radio source. However, the more extended radio structure shows that energetic events have taken place in the innermost few hundred parsees of NGC 4438. The interstellar medium of NGC 4438 may show at once the impact of nuclear energy input (from an AGN or cocooned starburst), perturbation by the companion NGC 4435, and interaction with the dense intergalactic medium in the Virgo core.

Keel, William C.↗
NASA NTRS1990

The early ISM and galaxy formation

Current ideas about galaxy formation are reviewed, with particular attention to when and how it occurred, and what it might have looked like. It is argued that galaxy formation is more recent than originally predicted. Suggestions are presented as to how current observations of distant objects may be interpreted within the cold dark matter theory for the origin of structure.

White, Simon D. M.↗
NASA NTRS1994

Dynamics and X-ray emission of a galactic superwind interacting with disk and halo gas

There is a general agreement that the conspicuous extranuclear X-ray, optical-line, and radio-contiuum emission of starbursts is associated with powerful galactic superwinds blowing from their centers. However, despite the significant advances in observational studies of superwinds, there is no consensus on the nature of the emitting material and even on the emission mechanisms themselves. This is to a great extent a consequence of a poor understanding of dynamical processes in the starburst superwind regions. To address this issue, we have conducted two-dimensional hydrodynamical simulations of galactic superwinds. While previous similar studies have used a single (disk) component to represent the ISM of the starburst galaxy, we analyze the interaction of the wind with a two-component disk-halo ambient interstellar medium and argue that this two-component representation is crucial for adequate modeling of starbursts. The emphasis of this study is on the geometry and structure of the wind region and the X-ray emission arising in the wind material and the shocked gas in the disk and the halo of the galaxy. The simulation results have shown that a clear-cut bipolar wind can easily develop under a range of very different conditions. On the other hand, a complex 'filamentary' structure associated with the entrained dense disk material is found to arise within the hot bubble blown out by the wind. The flow pattern within the bubble is dominated equally by the central biconic outflow and a system of whirling motions r elated to the origin and development of the 'filaments'. The filament parameters make them a good candidate for optical-emission-line filamentary gas observed in starburst halos. We find that the history of mass and energy deposition in the starburst region of the galaxy is crucial for wind dynamics. A 'mild' early wind, which arises as a result of the cumulative effect of stellar winds from massive stars, produces a bipolar vertical cavity in the disk and halo gas without strongly affecting the gaseous disk, thus creating conditions for virtually free vertical escape of the hot gas at the later, much more violent supernova-dominated phases of the starburst. We calculate the luminosity, mass, and effective temperature of the X-ray emitting gas in the 'soft' (0.1 to 0.7 keV, 0.7 to 2.2 keV, and 0.1 to 2.2 keV) and 'hard' (1.6 to 8.3 keV) energy bands and estimate the contribution of different gaseous components to the X-ray flux in these bands. Analysis of these parameters enables us to make conclusions regarding the nature of the X-ray-emitting material. We have inferred that the bulk of the soft thermal X-ray emission from starbursts arises in the wind-shocked material of the disk and halo gas rather than in the wind material itself. This enables us to predict that the integrated soft X-ray spectra of starbursts need not show an overabundance of heavy elements which are believed to be produced copiously in the centers of starbursts. Unlike soft X-ray emission, the hard component of thermal X-ray emission is found to originate in the wind material ejected from the starburst region. However, the derived ratio of hard-to-soft X-ray luminosities is too small compared to that observed in starbursts. We conclude therefore that the observed hard X-ray emission of starbursts is probably not associated with the thermal emission of hot wind or ambient shocked gas. Typical temperatures of the bulk of the soft X-ray-emitting material in our very different models have been found to agree well with the ones estimated on the basis of the ROSAT data for the soft component of X-ray emission of nearby starbursts. We predict that temperatures of the extranuclear soft X-ray-emitting gas in starburst galaxies with heavy element abundances near solar should be close to T(sub Xs = 2 to 5 x 10(exp 6)K.

Suchkov, Anatoly A.↗
NASA NTRS2009

Organic Chemistry in Space

Astronomical observations, theoretical modeling, laboratory simulation and analysis of extraterrestrial material have enhanced our knowledge of the inventory of organic matter in the interstellar medium (ISM) and on small bodies such as comets and asteroids (Ehrenfreund & Charnley 2000). Comets, asteroids and their fragments, meteorites and interplanetary dust particles (IDPs), contributed significant amounts of extraterrestrial organic matter to the young Earth. This material degraded and reacted in a terrestrial prebiotic chemistry to form organic structures that may have served as building blocks for life on the early Earth. In this talk I will summarize our current understanding of the organic composition and chemistry of interstellar clouds. Molecules of astrobiological relevance include the building blocks of our genetic material: nucleic acids, composed of subunits such as N-heterocycles (purines and pyrimidines), sugars and amino acids. Signatures indicative of inheritance of pristine and modified interstellar material in comets and meteorites will also be discussed.

Charnley, Steven↗
NASA NTRSDate not supplied

Printed Flexible Sensors for NASA Applications

As human spaceflight pushes beyond Low Earth Orbit (LEO), resupply of consumables becomes a significant challenge. One solution to this problem is In-Space Manufacturing (ISM), the capability to perform on-demand manufacturing and repair of consumables in an in-space environment. ISM offers significant flexibility to missions as it allows for a high degree of tailorability and reduction in launch mass. Leveraging advancements in fabrication, repair and recycling, ISM provides a highly sustainable and affordable solution to Exploration mission operations and logistics. In this talk, advances in printed electronics and sensors, ranging from nanomaterial ink development and hands-free fabrication methodologies to devices will be presented. Applications presented will include sensors for crew health monitoring, structural health monitoring and power generation.

sensors↗
NASA NTRS2018

The HR 4796A Debris System: Discovery of Extensive Exo-Ring Dust Material

The optically and IR-bright and starlight-scattering HR 4796A ringlike debris disk is one of the most- (and best-) studied exoplanetary debris systems. The presence of a yet-undetected planet has been inferred (or suggested) from the narrow width and inner/outer truncation radii of its r = 1farcs05 (77 au) debris ring. We present new, highly sensitive Hubble Space Telescope (HST) visible-light images of the HR 4796A circumstellar debris system and its environment over a very wide range of stellocentric angles from 0farcs32 (23 au) to ≈15'' (1100 au). These very high-contrast images were obtained with the Space Telescope Imaging Spectrograph (STIS) using six-roll PSF template–subtracted coronagraphy suppressing the primary light of HR 4796A, with three image-plane occulters, and simultaneously subtracting the background light from its close angular proximity M2.5V companion. The resulting images unambiguously reveal the debris ring embedded within a much larger, morphologically complex, and biaxially asymmetric exo-ring scattering structure. These images at visible wavelengths are sensitive to and map the spatial distribution, brightness, and radial surface density of micron-size particles over 5 dex in surface brightness. These particles in the exo-ring environment may be unbound from the system and interacting with the local ISM. Herein, we present a new morphological and photometric view of the larger-than-prior-seen HR 4796A exoplanetary debris system with sensitivity to small particles at stellocentric distances an order of magnitude greater than has previously been observed.

starlight-scattering HR 4796A↗
NASA NTRS2007

Optically Transparent Split-Ring Antennas for 1 to 10 GHz

Split-ring antennas made from optically transparent, electrically conductive films have been invented for applications in which there are requirements for compact antennas capable of operation over much or all of the frequency band from 1 to 10 GHz. Primary examples of such applications include wireless local-area networks and industrial, scientific, and medical (ISM) applications. These antennas can be conveniently located on such surfaces as those of automobile windows and display screens of diverse hand-held electronic units. They are fabricated by conventional printed-circuit techniques and can easily be integrated with solid-state amplifier circuits to enhance gain. The structure of an antenna of this type includes an antenna/feed layer supported on the top or outer face of a dielectric (e.g., glass) and, optionally, a ground layer on the bottom or inner face of the substrate. The ring can be in the form of either a conductive strip or a slot in the antenna/feed layer. The ring can be of rectangular, square, circular, elliptical, or other suitable shape and can be excited by means of a microstrip, slot line, or coplanar waveguide. For example, the antenna shown in the figure features a square conductive-strip split ring with a microstrip feed. In general, an antenna fed at its external boundary in the manner of this invention presents very high impedance, thereby creating an impedance-matching problem. Splitting the ring . that is, cutting a notch through the ring . offers a solution to the problem in that the notch fixes the location of maximum electric field, which location is directly related to the impedance. Thus, an excellent impedance match can be achieved through proper choice of the location of the notch. In geometric layout, such a ring antenna structure is typically between 1.4 and 1.3 the size of a patch antenna capable of operating in the same frequency range. This miniaturization of the antenna is desirable, not only because it contributes to overall miniaturization of equipment, but also because minimization of the extent of the optically transparent, electrically conductive film helps to minimize the electrical loss associated with the surface resistance ( 5 ohms per square) of the transparent, electrically conductive film material. Incidentally, even at 5 ohms per square, this surface resistance is significantly less than that of indium tin oxide film (typically > 25 ohms per square), which, heretofore has been the transparent, electrically conductive film material of choice. At the time of writing this article, information on the composition of the lower-resistance film used in the antennas of this invention was not available.

Lee, Richard Q.↗
NASA NTRSDate not supplied

Development of Aluminum Feedstock for Additive Manufacturing

The rapid evolution of materials science and manufacturing technologies in recent years has offered new pathways to manipulate materials for bespoke manufacturing. Here we aim to develop feedstocks for applications such as radiator panels, fuel tanks, and structural components for outfitting. As a strong, light weight and thermally conductive material aluminum is ideal for these applications. An often-overlooked source of aluminum waste is food packaging used on the International Space Station. Reusing this waste stream will reduce the cost and logistics of regular sparing. In Space Manufacturing (ISM) will utilize this technology is such areas as sparing and outfitting. However, processing aluminum can present challenges, especially in the context of additive manufacturing and sintering, due to its high reactivity and tendency to form a tenacious oxide layer. Identifying appropriate binders and sintering profiles can overcome these challenges. Herein we present our work on obtaining aluminum powder derived from food packaging, binder selection for aluminum feedstock, and a demonstration of bound metal deposition printing.

aluminum↗
NASA NTRS2005

Interstellar PAH Analogs in the Laboratory: Comparison with Astronomical Data

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the near-UV and visible range. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high-sensitivity spectroscopy and directly compared to the astronomical data. Preliminary conclusions from the comparison of the laboratory data with astronomical observations will also be presented.

Salama, Farid↗
NASA NTRS2005

Interstellar PAH in the Laboratory and in Space. What have we Learned from the New Generation of Laboratory and Observational Studies?

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-UV and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong VUV radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high-sensitivity spectroscopy and directly compared to the astronomical data. The electronic bands measured for ionized PAH are found to be intrinsically broad (about 20 cm(sup -1)) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10 cm(sup -1)). The laboratory data are discussed and compared with recent astronomical spectra of large and narrow DIBs and with the spectra of circumstellar environments of selected carbon stars and the implications for the interstellar PAH population are derived. Preliminary results also show that carbon nanoparticles are formed during the short residence time of the precursors in the plasma.

Salama, Farid↗
NASA NTRS2005

PAHs and the Diffuse Interstellar Bands. What have we Learned from the New Generation of Laboratory and Observational Studies?

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrophysics is to reproduce (in a realistic way) the physical conditions that exist in the emission and/or absorption interstellar zones, An extensive laboratory program has been developed at NASA Ames to characterize the physical and chemical properties of PAHs in astrophysical environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. In particular, laboratory experiments provide measurements of the spectral characteristics of interstellar PAH analogs from the ultraviolet and visible range to the infrared range for comparison with astronomical data. This paper will focus on the recent progress made in the laboratory to measure the direct absorption spectra of neutral and ionized PAHs in the gas phase in the near-W and visible range in astrophysically relevant environments. These measurements provide data on PAHs and nanometer-sized particles that can now be directly compared to astronomical observations. The harsh physical conditions of the IS medium - characterized by a low temperature, an absence of collisions and strong V W radiation fields - are simulated in the laboratory by associating a molecular beam with an ionizing discharge to generate a cold plasma expansion. PAH ions are formed from the neutral precursors in an isolated environment at low temperature (of the order of 100 K). The spectra of neutral and ionized PAHs are measured using the high sensitivity methods of cavity ring down spectroscopy (CRDS). These experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high- sensitivity spectroscopy and directly compared to the astronomical data. The electronic bands measured for ionized PAH are found to be intrinsically broad (about 20/cm) while the bands associated with the neutral precursors are narrower (of the order of 2 - 10/cm).

Salama, Farid↗
NASA NTRS2005

Spectroscopy of neutral and ionized PAHs. From laboratory studies to astronomical observations

Polycyclic Aromatic Hydrocarbons (PAHs) are an important and ubiquitous component of carbon-bearing materials in space. PAHs are the best-known candidates to account for the IR emission bands (UIR bands) and PAH spectral features are now being used as new probes of the ISM. PAHs are also thought to be among the carriers of the diffuse interstellar absorption bands (DIBs). In the model dealing with the interstellar spectral features, PAHs are present as a mixture of radicals, ions and neutral species. PAH ionization states reflect the ionization balance of the medium while PAH size, composition, and structure reflect the energetic and chemical history of the medium. A major challenge for laboratory astrochemistry is to reproduce (in a realistic way) the physical conditions that are associated with the emission and absorption interstellar zones. An extensive laboratory program has been developed at NASA Ames to assess the physical and chemical properties of PAHs in such environments and to describe how they influence the radiation and energy balance in space and the interstellar chemistry. PAHs, neutrals and ions, are expanded through a pulsed discharge nozzle (PDN) and probed with high-sensitivity cavity ringdown spectroscopy (CRDS). These laboratory experiments provide unique information on the spectra of free, cold large carbon molecules and ions in the gas phase from the ultraviolet and visible range to the near-infrared range. Intrinsic band profiles and band positions of cold gas-phase PAHs can now be measured with high-sensitivity spectroscopy and directly compared to the astronomical data. Preliminary conclusions from the comparison of the laboratory data with astronomical observations of interstellar and circumstellar environments will also be discussed.

Salama, Farid↗