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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 325 records · Page 18
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NASA NTRS1987

IR excesses in Be stars

Infrared excesses are empirically derived for a sample of bright Be stars based on IRAS data and previously published near-infrared photometry. The excesses are compared with published H-alpha luminosities and are found to be correlated. The data are compared with the theoretically expected relation between the sum of free-free and free-bound continua and the H-alpha recombination-line intensity from a common envelope. The inclusion of temperature and optical-depth effects is necessary to produce agreement between observations and theory. No significant correlation is detected between L(IR)/L(H-alpha) ratios and rotational velocities.

Chokshi, Arati↗
NASA NTRS1987

The IR emission features - Emission from PAH molecules and amorphous carbon particles

Given the current understanding of polycyclic aromatic hydrocarbons (PAHs), the spectroscopic data suggest that are at least two components which contribute to the interstellar emission spectrum: (1) free molecule-sized PAHs producing the narrow features and (2) amorphous carbon particles (which are primarily composed of an irregular 'lattice' of PAHs) contributing to the broad underlying components. An exact treatment of the IR fluorescence from highly vibrationally excited large molecules demonstrates that species containing between 20 and 30 carbon atoms are responsible for the narrow features, although the spectra match more closely with the spectra of amorphous carbon particles. It is concluded that, since little is known about the spectroscopic properties of free PAHs and PAH clusters, much laboratory work is required along with an observational program focusing on the spatial characteristics of the spectra.

Allamandola, L. J.↗
NASA NTRS1986

Thermal testing by internal IR heating of the FEP module

A spacecraft module, to be integrated with the FLTSATCOM spacecraft, was tested in a simulated orbit environment separate from the host spacecraft. Thermal vacuum testing of the module was accomplished using internal IR heating rather than conventional external heat sources. For this configuration, the technique produced boundary conditions expected for flight to enable verification of system performance and thermal design details.

Nathanson, D. M.↗
NASA NTRS1988

The detection of high-velocity outflows from M8E-IR

A high-resolution (0.059/cm) M band (4.6 micron) spectrum of the embedded young stellar object M8E-IR is presented and discussed. The spectrum shows strong absorption to large blueshifts in the rotational lines of the fundamental vibrational band, v = 1-0, of CO. The absorption is interpreted as being due to gas near to, and flowing from, the central object. The outflowing gas is warm (95-330 K) and consists of discrete velocity components with the very high velocities of 90, 130, 150, and 160 km/s. On the basis of a simple model, it is estimated that the observed outflows are less than 100 yr old.

Mitchell, George F.↗
NASA NTRS1988

A spectrophotometric study of IR Gem at outburst and quiescence

Optical spectra with 2.5-A resolution obtained throughout the orbit of IR Gem during a five-day sequence beginning at an outburst state and ending at quiescence are compared with B magnitude and IUE spectra obtained throughout other quiescent-state orbits. No obvious second component is found in the emission lines. In contrast to previous results, little high-excitation He II 4686-A emission is noted, and no variation of the equivalent widths of the Balmer emission is found over the orbital cycle. The results suggest that large changes in the excitation level and in the modulation from a heated zone can take place during different quiescent states, possibly due to the interoutburst phase.

Feinswog, Laurie↗
NASA NTRS1990

FT-IR spectroscopic studies of polycyclic aromatic hydrocarbons

Proper assessment of the hypothesis which correlates polycyclic aromatic hydrocarbons (PAHs) with the unidentified infrared emission bands requires additional experimental laboratory data. In order to address this need, thermal infrared emission studies were performed on a subset of PAHs suggested to be of astrophysical importance. It was proposed that infrared emission from interstellar PAHs occurs following absorption of an ultraviolet photon. Since energy transfer to the ground electronic state can be rapid for a species in which intersystem crossing is negligible, the emission spectrum may be viewed as resulting from an equilibrium vibrational temperature (Leger and d'Hendecourt, 1987). This has been the basis for using infrared absorption spectra to calculate the corresponding emission spectra at various temperatures. These calculations were made using room temperature infrared absorption coefficients instead of those at the temperature of interest because of the latter's unavailability. The present studies are designed to address the differences between the calculated and experimental thermal emission spectra and to provide information which will be useful in future ultraviolet induced infrared fluorescence studies. The emission spectra have been obtained for temperatures up to 825K using an emission cell designed to mount against an external port of an FT-IR spectrometer. These spectra provide information concerning relative band intensities and peak positions which is unavailable from previous calculations.

Salisbury, D. W.↗
NASA NTRS1988

The Santa Barbara Research Center multimodule shortwave IR linear array and scene simulator

Alignment test results and scene simulator imagery are presented for a 1 x 1280 element linear assembly consisting of 5 end-butted modules. The modules include a Si readout chip, a 256 element photovoltaic HgCdTe detector array, and a Si/sapphire carrier. At 145 K, the operation of the LPE shortwave HgCdTE detector array yielded Resistance Area products of 420,000 ohm-sq cm. The results demonstrate the ability to fabricate high-performance, long linear multimodule shortwave IR focal planes for space applications.

Cizdziel, Philip↗
NASA NTRS1989

The detection of an IR excess toward the globular cluster RV Tauri variable M28 V17

The paper presents the results of a search for IR emission excesses toward three globular cluster stars. Two of the stars are RV Tau variables (M28 V17 and M5 V85) and one is believed to be a W Vir variable (M5 V42) which is historically linked to the RV Tau class. Consideration is given to the implications of the observed detections, in particular, the establishment of M28 V17 as a star in a globular cluster that is indistinguishable from the Preston type A subclass.

Nook, Mark A.↗
NASA NTRS1990

Tunable diode laser IR spectrometer for in situ measurements of the gas phase composition and particle size distribution of Titan's atmosphere

A new instrument, the Probe Infrared Laser Spectrometer (PIRLS), is described for in situ sensing of the gas composition and particle size distribution of Titan's atmosphere on the NASA/ESA Cassini mission. For gas composition measurements, several narrow-band (0.0001/cm) tunable lead-salt diode lasers operating near 80 K at selected mid-IR wavelengths are directed over a path length defined by a small reflector extending over the edge of the probe spacecraft platform; volume mixing ratios of 10 to the -9th should be measurable for several species of interest. A cloud-particle-size spectrometer using a diode laser source at 780 nm shares the optical path and deployed reflector; a combination of imaging and light scattering techniques is used to determine sizes of haze and cloud particles and their number density as a function of altitude.

Webster, Christopher R.↗
NASA NTRS1990

Analytic model of an IR radiation heat pipe

An IR radiation heat pipe made from multilayer insulation blankets and proposed to be used aboard spacecraft to transfer waste heat was modeled analytically. A circular cross section pipe 9-in. in diameter, 10-ft long, with a specular reflectivity of 0.94 was found to have an efficiency of 58.6 percent. Several key parameters were varied for the circular model to understand their significance. In addition, square and triangular cross section pipes were investigated.

Hoffman, Pamela J.↗
NASA NTRS1990

Optical and near-IR study of LMC HII region N11AB

N11 (DEM 34), complex HII region located about 4 degrees from the center of the LMC bar, is a very interesting giant interstellar shell. It has a complicated structure and motion. It is located on the edge of an HI concentration. This is the progress report of the study of its two components, A and B at the optical and near-IR wavelengths to investigate stars, dust and ionized gas associated with them. N11A is a compact high-excitation blob and N11B is a bright HII region in this complex, which embeds OB association Lucke-Hodge 10.

Lee, Myung Gyoon↗
NASA NTRS1990

CO excitation in four IR luminous galaxies

The correlation between the CO and far infrared luminosities of spiral galaxies is well established. The luminosity ration, L sub FIR/L sub CO in IR luminous active galaxies is, however, systematically five to ten times higher than in ordinary spirals and molecular clouds in our Galaxy. Furthermore, the masses of molecular hydrogen in luminous galaxies are large, M (H2) approx. equals 10(exp 10) solar magnitude, which indicates the observed luminosity ratios are due to an excess of infrared output, rather than a deficiency of molecular gas. These large amounts of molecular gas may fuel luminous galaxies through either star formation or nuclear activity. This interpretation rests on applying the M (H2)/L sub CO ratio calibrated in our Galaxy to galaxies with strikingly different luminosity ratios. But are the physical conditions of the molecular gas different in galaxies with different luminosity ratios. And, if so, does the proportionality between CO and H2 also vary among galaxies. To investigate these questions researchers observed CO (2 to 1) and (1 to 0) emission from four luminous galaxies with the Institute for Radio Astronomy in the Millimeter range (IRAM) 30 m telescope. Researchers conclude that most of the CO emission from these Arp 193, Arp 220, and Mrk 231 arises in regions with moderate ambient densities similar to the clouds in the Milky Way molecular ring. The emission is neither from dense hot cloud cores nor from the cold low density gas characteristic of the envelopes of dark clouds.

Radford, Simon J. E.↗
NASA NTRS1990

Issues and directions in IR detector readout electronics

An introduction to the major issues encountered in the readout of imaging detector arrays in the infrared are presented. These include circuit issues such as multiplexing, buffering, and noise, as well as materials issues. Future directions in infrared readout electronics will also be discussed. These include on-chip signal processing and advanced hybridization schemes. Finally, recent work at Columbia on 2DEG-charge coupled devices for IR detector multiplexing are described.

Fossum, Eric R.↗
NASA NTRS1990

Ultraviolet, visual, and infrared studies of galactic extreme emission line objects with very large IR-excess

Some preliminary results of a study of extreme emission line objects (EELOs) are presented. These stars are selected from H alpha emission line stars having a strong IR excess. The study is based on multiwavelength photometric and spectroscopic observations. Special attention is paid to the detailed study of the correlation between spectroscopic and photometric variations, which indicate the activity of the star. The ultraviolet and infrared extinction characteristics of the circumstellar material are given special attention.

Dewinter, D.↗
NASA NTRS1990

Optical and near-IR imaging observations of comet Austin 1989c1

Near-nucleus imaging observations of comet Austin (1989c1) were carried out by the Japanese CCD imaging team. Six telescopes were used to monitor the time variation of the near-nucleus images in C2, CN, H2O, and Na continuum in the optical region, and in J, H, and K bands in the near-IR region. A featureless, round shape of the comet was revealed in all images. Although some of the jet features are recognized by using an image enhancement technique, the azimuthal difference of the intensity distribution is about 10 percent. The images in the H2O band show complex ion structures near the nucleus.

Watanabe, J.↗
NASA NTRS1991

Cryo-mechanical tests of Ames 24E2 IR-black coating

In addition to the ambient condition tape test, five mechanical tests of the IR-black coating, Ames 24E2, were performed at either liquid helium or liquid nitrogen temperatures. Tensile strain in the coating at liquid nitrogen temperature was measured up to values of 4E-3, both before and after the coating was cycled down to liquid helium temperature. When applied to an aluminum substrate which was then bent in liquid nitrogen, the aluminum substrate always failed (permanently deformed) well before the coating failed. Sinusoidal accelerations up to 45 Gs in liquid nitrogen and 25 Gs in liquid helium did not crack or otherwise visibly damage the coating. Both sinusoidal and random acceleration at about 90 K of a representative baffle vane structure, at frequencies from 10 to 2000 Hz and up to 15 Gs, did not damage the coating, even at the intersection of a baffle with the telescope tube. Thus on a macroscopic level, cryogenic cooling and various levels of acceleration and strain did not affect this coating. However, on a microscopic scale, some loose particles were found associated with several tests. Outgassing data are also given.

Smith, Sheldon M.↗
NASA NTRS1990

Hydrocarbon emission features in the IR spectra of warm supergiants

Observations in the 3-13 micron range are presented for two objects possessing the unidentified 21-micron feature, IRAS 22272 and IRAS 07134, which were obtained in the course of search for circumstellar aromatic hydrocarbon (PAH) emission bands. The 3.3 and 6.2 micron bands are attributed to circumstellar PAH molecules, and the 6-9 micron plateau and the 12- and 6.9-micron lines are attributed to larger, aromatic hydrocarbon clusters. These are the coolest stars known to exhibit the IR emission bands. The 21-micron feature is conjectured to also originate in a carbonaceous carrier.

Buss, R. H., Jr.↗