SEARCH · Engineering Papers

Results for “Co”

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.

SourceResearch connectionFrom yearThrough year

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

At least 1,333 records · Page 74

All sources NASA NTRS DOE OSTI

NASA NTRS1983

On photochemical heating of cometary comae - The cases of H2O and CO-rich comets

It is found that the effect of energy addition due to photochemical processes in the cometary coma on the heating and accelerating of the expanding neutral gas is limited by the kinematic property of the energy transfer from the energetic fragments to the bulk flow. The effective scale length of the photochemical zone for an H2O comet is estimated to be only 10% of the dimension of the collision region due to the large mass ratio of H atom and H2O molecule. When this physical property is taken into consideration, the H2O gas is found to be expanding at a highly supersonic speed. In addition, it is shown that the addition of a mixture of CO and/or CO2 molecules in a medium-bright comet with total production rate of 10 to the 29th molecules/s would not change this conclusion since the photodissiation length scales of these molecules are a factor of 10-30 larger than that of the H2O molecules. Thus, most of the CO and CO2 molecules will be dissociated outside of the collision zone without depositing the excess kinetic energy to the neutral atmosphere. However, if the gas production rate is controlled by CO or CO2, the dimension of the collision zone of a CO comet at 1 AU will be increased by a factor of seven. The photochemical heating due to CO dissociation would thus be more effective, causing the atmospheric flow to be weakly supersonic. It is concluded that the neutral gas outflows from H2O comets and CO comets could be substantially different.

Ip, W.-H.↗

NASA NTRS1984

4.6 micron absorption features due to solid phase CO and cyano group molecules toward compact infrared sources

Spectra obtained at a resolving power of 840, for seven protostellar sources in the region of the 4.67-micron fundamental vibrational band of CO, indicate that the deep absorption feature in W33A near 4.61 microns consists of three features which are seen in other sources, but with varying relative strength. UV-irradiation laboratory experiments with 'dirty ice' temperature cycling allow the identification of two of the features cited with solid CO and CO complexed to other molecules. Cyano group-containing molecules have a lower vapor pressure than CO, and can therefore survive in much warmer environments. The formation and location of the CO- and CN-bearing grain mantles and sources of UV irradiation in cold molecular clouds are discussed. Plausible UV light sources can produce the observed cyano group features, but only under conditions in which local heat sources do not cause evaporation of the CO molecules prior to their photoprocessing.

Lacy, J. H.↗

NASA NTRS1987

CO observations of nearby galaxies and the efficiency of star formation

The CO distributions and total molecular content of 160 galaxies were observed using the 14 meter millimeter telescope of the FCRAO. For the luminous, relatively face-on Sc galaxies, the azimuthally averaged CO distributions are centrally peaked, while for the Sb and Sa galaxies the Co distributions often exhibit central CO holes up to 5 kpc across. None of the Sc galaxies have CO distributions which resemble the Milky Way. A general correlation was found between total CO and IR luminosities in galaxies. The scatter in this relation is highly correlated with dust temperature. No strong correlation of IR luminosities was found with HI masses, and it was thereby concluded that the infrared emission is more directly tied to the molecular content of galaxies. It is suggested that galaxies which have high Star Formation Effiencies (SFEs) produce more stars per unit molecular mass, thereby increasing the average temperature of the dust in the star forming regions. Irregular galaxies and galaxies previously identified as mergers have the highest observed star formation efficiencies. For the mergers, evidence was found that the IR/CO luminosity ratio increases with the merger age estimated by Joseph and Wright (1985).

Young, Judith S.↗

NASA NTRS1987

New CO and HCN sources associated with IRAS carbon stars

Emission of CO and HCN was detected in 22 out of a sample of 53 IRAS sources classified as unidentified carbon-rich objects. The sample was selected according to the presence of the silicon carbide feature as revealed by low-resolution spectra. The molecular line widths indicate that the CO and HCN emission arises from the circumstellar envelopes of very highly evolved stars undergoing mass loss. The visible stars tend to be deficient in CO as compared with unidentified sources. Most the detected CO and HCN IRAS stars are distinct and thick-shelled objects, but their infrared and CO luminosities are similar to those of IRC + 102156 AFGL and IRC-CO evolved stars. The 12 micron flux seems to be a good indicator of the distance, hence a guide for molecular searches.

NGUYEN-Q-RIEU↗

NASA NTRS1987

Systematic properties of CO emission from galaxies. I - Luminosity function

A sensitive survey of normal galaxies covering a wide range of luminosities and morphological types is combined with galaxy observations in the literature to provide a sample for statistical study. The global CO emission of these galaxies is extrapolated by modeling the galaxies with an exponential radial profile. The maximum-likelihood distribution functions of CO luminosity and CO/H I flux ratio are similar in behavior. Both have long tails of bright galaxies. However, the typical galaxy has a CO luminosity of about 10 to the 6th Jy km/s Mpc-squared or less and a CO/H I ratio of the order of 10 or less. Averages of the distributions of CO luminosity and CO/H I flux ratio are higher for galaxies of Hubble type Sb-Sbc than for groups of earlier or later types. Quantitative estimates of the possible error sources in the conversion of CO luminosity to molecular mass indicates that the peaking of CO emission at intermediate types is a fairly confident result.

Verter, Frances↗

NASA NTRS1987

The abundance of interstellar CO

Data from recent observations of interstellar CO column densities are compiled in tables and graphs and compared with the predictions of theoretical models. The energy-level structure of CO and the excitation of interstellar CO are discussed; UV-absorption and IR line observations are characterized; and techniques used to estimate the CO column density from mm-wavelength observations (based on calibration of the CO line intensity with the column density of H2) are described in detail. Consideration is then given to CO chemistry under interstellar-cloud conditions (isotope fractionation and photodissociation) and models for diffuse, translucent, and dense clouds. A number of unsolved problems requiring additional observations or laboratory investigations are identified.

Van Dishoeck, Ewine F.↗

NASA NTRS1988

The condensation and vaporization behavior of H2O:CO ices and implications for interstellar grains and cometary activity

IR spectroscopy has been used to ascertain several parameters associated with CO, H2O, and H2O:CO ices' physical behavior. Since CO is noted to be capable of condensing into H2O-rich ices at temperatures that are twice as high as those required for condensation in pure CO, CO is able to condense onto H2O-rich ice grains at temperatures of up to 50 K. CO's presence in H2O ice modestly enhances the effective volatility of the H2O. Attention is given to the implications of these results for cometary models generally and the question of cometary formation specifically.

Sandford, Scott A.↗

NASA NTRS1989

A millimeter-wave survey of CO emission in Seyfert galaxies

Emission in the 115 GHz 1-0 line of CO has been detected in 18 Seyfert galaxies in a sample of 43. The CO properties of 29 Seyferts in the Revised Shapley Ames Catalog (RSA) are compared with the CO properties of normal galaxies of the same Hubble type. These RSA type 2 Seyferts have an average ratio of CO-to-blue luminosity that is about twice as large as that of the normal galaxies, but the RSA type 1 Seyferts have normal CO luminosities. The RSA type 2 Seyfert galaxies have an unusually large average ratio of CO luminosity-to-H I mass compared to normal disk galaxies. The RSA type 2 Seyferts have an average far-IR luminosity that is about four times larger than a non-Seyfert comparison sample, while the RSA type 1 Seyferts are not significantly more luminous than the non-Seyferts. The result imply that the two classes of Seyferts are intrinsically different from one another and that one class cannot evolve into another in less than a few million years.

Heckman, T. M.↗

NASA NTRS1990

ISS and TPD study of the adsorption and interaction of CO and H2 on polycrystalline Pt

The adsorption and interaction of CO and H2 on polycrystalline Pt has been studied using ion scattering spectroscopy (ISS) and temperature programmed desorption (TPD). The ISS results indicate that the initial CO adsorption on Pt takes place very rapidly and saturates the Pt surface with coverage close to a monolayer. ISS also shows that the CO molecules adsorb at an angular orientation from the surface normal and perhaps parallel to the surface. A TPD spectrum obtained after coadsorbing C-12 O-16 and C-13 O-18 on Pt shows no isotopic mixing, which is indicative of molecular CO adsorption. TPD spectra obtained after coadsorbing H2 and CO on polycrystalline Pt provides evidence for the formation of a CO-H surface species.

Melendez, Orlando↗

NASA NTRS1990

In situ analysis of CO during chemisorption and oxidation on graphite: Supported Pt by FTIR-microspectrometry

For chemisorption and oxidation on Pt/HOPG (highly-orientated pyrolytic) graphite, reflectance Fourier Transform Infrared (FTIR)-microspectrometry reveals a variable state and reactivity for CO. Even for model surface science systems, where surface heterogeneity is minimal, surface diffusion may be too slow relative to the reaction rate to avoid segregation of reactants into surface islands under steady-state conditions. Thus in CO oxidation on Pt (where the relevant surface diffusion coefficients are such that D sub O less than D sub CO) then reactant CO islands exists at the perimeters of which the surface reaction is thought to occur. Furthermore CO can chemisorb on metals in linear and bridge forms to extents which vary with precise faces predominantly exposed coverage, etc. Infrared has long been used to probe the nature of adsorbed CO on model film and heterogeneous surfaces, but it may now be that FTIR-microspectrometry will allow the state of this adsorbate and reactant to be investigated with a spatial resolution of 4.4 microns on model (and real) catalytic surfaces.

Self, Valerie A.↗

NASA NTRS1990

Applications of low temperature CO-oxidation catalysts to breathable gases

Modifications of tin oxide/precious metal catalysts described for use in CO2 lasers have also been developed for use in other applications; namely, as low temperature CO oxidation components in fire escape hoods/masks for mines, aircrafts, hotels, and offices and in sealed environments, such as hyperbaric chambers and submarines. Tin oxide/precious metal catalysts have been prepared on a variety of high surface area cloth substrates for application in fire escape hoods. These show high and stable CO oxidation capability (10 to the 4th power ppm CO reduced to 10 to the 1st power ppm CO) at GHSV of 37,000 h(-1) with water saturated inlet gas at body heat (37 C) and below. Water vapor plays an important role in the surface state/performance of tin oxide catalyst. Water-resistant formulations have been produced by the introduction of transition metal promoters. Tin oxide/precious metal catalysts have also been developed for CO oxidation in the North Sea diving environment. These are currently in use in a variety of hyperbaric chambers and diving vehicles. Ambient temperature operation and resistance to atmospheric water vapor have been demonstrated, and as a result, they offer a viable alternative to hopcalite or heated catalyst systems. A new range of non-tin oxide based low temperature CO oxidation catalysts is described. They are based on reducible metal oxides promoted with previous metals. Preliminary data on selected materials in the form of both cloth artifacts and shaped pellets are presented. They are expected to be applicable both to the breathable gas application area and to CO2 lasers.

Noordally, Ehsan↗

NASA NTRS1990

The variations of CO and O3 concentrations in a region subject to biomass burning

Carbon monoxide (CO) and ozone (O3) concentrations have been observed in the Brazilian Amazon region, at a site strongly affected by biomass burning (Cuiaba, 16 deg S, 58 deg W). Time variations are described for the first long-term program of studying the effect of biomass burning on O3 and CO over a complete seasonal cycle, including the seasonal maxima of 1987 and 1988. In order to obtain elements for comparison, an identical observational program was maintained at a site totally outside of the direct influence of biomass burning (Natal, 6 deg S, 35 deg W). The biomass burning contribution to the Cuiaba concentrations of CO and O3 is very large. Diurnal maxima concentrations exceeded 90 ppbv O3 in 1987 and 120 ppbv O3 in 1988, in September. For the wet season, the monthly average ozone concentration in March-April is about 10 ppbv. During the month of maxima, September, the O3 concentration average was 41 ppbv for 1987 and 71 ppbv for 1988. The CO concentrations are about 90 ppbv in the wet season. In September, 460 ppbv and 660 ppbv of CO were observed for 1987 and 1988, respectively. At Natal the seasonal variation is of the order of a factor of 2. During the wet season, the concentrations of CO and O3 at both stations are about the same.

Kirchhoff, V. W. J. H.↗

NASA NTRS1990

The FCRAO extragalactic CO survey: Global properties of galaxies

Since stars form in molecular clouds, a critical element in studies of galaxy evolution is knowledge of the molecular content of a large sample of galaxies. To this end, researchers undertook a survey of CO emission from galaxies using the Fire College Radio Astronomy Observatory (FCRAO) 14-m millimeter telescope at 115 GHz. The aim was to better understand the differences found among and within galaxies with regard to the efficiency of star and cloud formation. The galaxies observed as part of the FCRAO Extragalactic CO Survey were selected on the basis of their optical or infrared properties. The galaxies observed thus far are (1) brighter than B sub T (sub o)=12.5 in the blue, or (2) brighter than 20 Jy at 100 microns. From major axis CO observations at 45 seconds resolution and spacing in over 200 galaxies, researchers determined the CO radial distributions, and derived global CO fluxes (cf. Kenney and Young 1988); H2 masses were derived using the conversion factor N(H2)/I sub CO=2.8 times 10 to the 20th power cm(-2)/K km s(-1)) (Bloemen et al. 1986). Here, researchers concentrate on the global galaxy properties within the sample. Neutral hydrogen (HI) masses for the sample galaxies were taken from Huchtmeier et al. (1983), blue luminosities and morphological types were taken from RC2. IR luminosities, colors, dust temperatures and dust masses were determined from coadded Infrared Astronomy Satellite (IRAS) data (Young et al. 1989). They have chosen to first compare absolute luminosities and masses in order to determine the slope and scatter in each correlation; next they investigate luminosity independent ratios in order to intercompare large and small galaxies.

Young, J. S.↗

NASA NTRS1990

High resolution CO images of Seyfert Galaxies

The CO (J = 1-0) emission of three Seyfert galaxies, NGC 3227, NGC 7469, and NGC 5033 was imaged. The CO emission in NGC 3227 and NGC 7469 appears as compact structures centered on the active nuclei, containing substantial fractions of the single-dish flux. In NGC 3227, 10 percent of the CO flux detected by the interferometer is contained within the ionized narrow-line region. The unresolved molecular gas concentrations in the nucleus of NGC 3227 imply a CO mass of 65 million solar masses concentrated within a diameter less than 50 pc. The CO emission in NGC 5033 is not detected at this resolution, implying a CO structure size of 20 to 60 arcsec. Continuum emission at 2.7 mm is not detected in any of the three galaxies. In the center of NGC 7469, the H2 mass is comparable to the dynamical mass. Kinematic studies of the detected gas reveal a rotational motion of the gas in NGC 3227 and NGC 7469, allowing identification of the gas in NGC 7469 with a nuclear starburst. These data are consistent with the idea that interactions between galaxies cause gas to concentrate in their nuclei thereby feeding starburst and Seyfert activity.

Meixner, M.↗

NASA NTRS1990

Observations of CO isotopic emission and the far-infrared continuum of Centaurus A

Researchers present maps of the CO-12(1=0) line and the 100 micron and 50 micron far-infrared emission of Centaurus A, as well as measurements of the CO-12(2-1), CO-13(1-0), and the C-18O(1-0) lines at selected positions. The observations were taken with the Swedish-ESO Submillimeter Telescope (SEST) and the CPC instrument on board the Infrared Astronomy Satellite (IRAS). The millimeter data show that the bulk molecular material is closely associated with the dust lane and contained in a disk of about 180 seconds diameter and a total molecular mass of about 2 x 10 to the 8th power solar mass. The total molecular mass of the disk and bulge is of the order of 3 x 10 to the 8th power solar mass. The molecular gas in the nucleus is warm with a kinetic temperature of the order of 15 K and a number density of 10 to the 3rd power to 3 x 10 to the 4th power cm(-3). Absorption features in the CO-12 and CO-13 lines against the nuclear continuum emission indicate that the properties of giant molecular clouds are comparable to those of the Galaxy. The far-infrared data show that to a good approximation the dust temperature is constant across the dust lane at a value of about 42 K. The ratio between the far-infrared luminosity and the total molecular mass is 18 solar luminosity/solar mass and close to the mean value obtained for isolated galaxies. A comparison of the CO-12(1-0) and the far-infrared data indicates that a considerable amount of the far-infrared emission is not intimately associated with massive star formation.

Eckart, A.↗

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 NTRS1992

Millimeter-wave observations of Saturn, Uranus, and Neptune - CO and HCN on Neptune

Saturn, Uranus, and Neptune were observed at millimeter wavelengths with the IRAM 30 m telescope. The major result is the detection of CO and HCN in Neptune's stratosphere, with respective mixing ratios of (6.5 +/- 3.5) x 10 exp -7 and (3 +/- 1.5) x 10 exp -10. CO seems to be present in Neptune's troposphere as well and to slowly decrease with altitude (scale height about 200 km). HCN is probably formed from reactions between CH3 and N, which can be supplied in sufficient amounts by escape from Triton's atmosphere. The origin of CO, however, is more problematic, because: (1) thermochemical models fail to reproduce the observed abundance by a factor of about 1000; and (2) an external source would require a very large flux of oxygen. CO appears to be at least 15 times less abundant on Uranus than on Neptune. Finally, an upper limit of 10 exp -7 for CO in Saturn's stratosphere suggests an internal origin for Saturnian CO.

Rosenqvist, Jan↗

NASA NTRS1992

First images of a possible CO(+)-tail of comet P/Schwassmann-Wachmann 1 observed against the dust coma background

Comet P/Schwassmann-Wachmann 1 was observed with the 2m-Ritchey-Cretien Telescope of the Bulgarian National Observatory, Rozhen, Bulgaria, using the CCD-camera and focal reducer of the Max-Planck-Institute for Aeronomy. Images were taken in a red continuum window and in the 2-0 A(exp 2)Pi - X(exp 2)Sigma(+) band of CO(+) located in the blue part of the spectrum. The red images reveal an extended dust coma. From a comparison of the red and blue images a dust reddening of 13.2 percent per 1000 A is derived. At 642 nm the magnitude of the comet with a square diaphragm of 4.5 arcsec is 16.6. The blue images, taken in the CO(+) band, show a significantly different brightness distribution which is interpreted as presence of a CO(+) coma and tail superimposed on the continuum. A column density of several 10(exp 10) CO(+) molecules cm(exp -2) is derived. The tail thickness of 10(exp 5) km is unexpectedly small. We estimate the CO(+) production rate to about 6 x 10(exp 26) CO(+) particles s(exp -1). This value does not support the idea that the outbursts of this comet are caused by crystallization of amorphous water ice.

Jockers, Klaus↗