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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 109 records · Page 6
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NASA NTRS1978

Infrared observations of the galactic center. III - 2.2 micron spectroscopy

Observations of the B-gamma line at 2.17 microns are presented for the central few parsecs of the galactic-center region. The surface-brightness distribution of the line with 3.3- and 6.6-arcsec resolution has been sampled in 25 locations. The results show that the ionized gas is concentrated within the central parsec of the galactic-center region; the fine-scale structure seen at 10 microns does not appear to be present in the ionized gas. For the central parsec (20 arcsec) the equivalent width of the B-gamma line is, within large uncertainties, independent of the 2-micron continuum flux; for radial distances of the order of 30 arcsec the line equivalent width drops significantly. A comparison of the B-gamma line strength with radio observations shows that the 2.2-micron extinction is consistent with the 2.7 mag determined from the reddening of late-type stars. Observations of the CO band at 2.3 microns in the central 30 arcsec are also presented; they strengthen the interpretation that the 2-micron flux arises from late-type giant stars.

Neugebauer, G.↗
NASA NTRS1978

Venus - The 17- to 38-micron spectrum

A far-IR emission spectrum of Venus covering the wavelength range from 17 to 38 microns is examined which was obtained on five nights at an altitude of 14 km with the 30-cm telescope of the NASA Lear Jet. The spectrum is found to be characterized by an overall continuum level with noticeable absorption shortward of 20 microns and longward of 30 microns as compared with a 245-K blackbody. The continuum level is taken as implying a continuous source of opacity in the Venusian atmosphere over the entire range from 17 to 38 microns with increased opacity shortward of 20 microns and longward of 30 microns. It is shown that a haze of sulfuric acid droplets can provide the necessary opacity and explain the observed depressions. A pressure level of roughly 200 mb is deduced for this spectrum.

Reed, R. A.↗
NASA NTRS1978

Observations of the 51.8 micron forbidden O III emission line in Orion

This letter reports observations of the 51.8-micron fine-structure transition p2: 3P(2) - 3P(1) for doubly ionized oxygen. The observed line strength in the Orion Nebula is (5 + or - 3) by 10 to the -15th power W/sq cm, in good agreement with the theoretical predictions of Simpson (1975). The observations are also consistent with the predicted line position, 51.8 microns. The line lies close to an atmospheric water-vapor feature at 51.7 microns but is sufficiently distant so that corrections for this feature are straightforward. Observations of the 51.8-micron forbidden O III line are particularly important, since the previously discovered 88-micron line from the same ion also is strong. This pair of lines should therefore yield new data about densities in observed H II regions; or else, if density data already are available from radio or other observations, the lines can be used to determine the differential dust absorption between 52 and 88 microns in front of heavily obscured regions.

Melnick, G.↗
NASA NTRS1979

The 4 to 8 micron spectrum of the galactic center

Observations of the complex Sgr A W(N) with a 28-arcsec beam and 1.5% spectral resolution are reported. Neither unidentified absorption features at 6.0 and 6.8 microns nor emission features at 6.2 and 7.7 microns were detected. The absence of the absorption features demonstrates that they are not characteristic of general interstellar extinction. The absence of emission features suggests that there is considerable distance between the ionized gas and the molecular clouds. The absence of 6.2- and 7.7-micron emission features also suggests that a feature previously seen at 3.3-3.4 microns is an absorption at 3.4 microns, and this absorption is apparently characteristic of interstellar extinction. The strength of the forbidden Ar II emission indicates an overabundance of argon. CO absorption seen at 4.67 microns indicates that saturation effects are not large, and there is evidently a large velocity dispersion in the line of sight to the infrared sources.

Willner, S. P.↗
NASA NTRS1979

Absolute spectral energy distribution of quasi-stellar objects from 0.3 to 10 microns

Energy distributions of 24 quasrs have been measured from 0.3 to 10 microns. In addition, optical emission-line strengths have been obtained for 35 quasars. The sample includes quasars discovered from both radio and optical surveys. Over the observed range of wavelengths the energy distributions are roughly characterized by a power law of slope -1, but there are vast differences in the shapes of individual spectra. In the rest frame the average slope between 1 and 3 microns is significantly steeper than the average slope between 0.3 and 1 micron; the power emitted at 0.3 and 3 microns is significantly greater than that emitted around 1 micron. On the basis of arguments of variability and the shape of the energy distribution between optical and radio wavelengths, it is concluded that the bulk of the radiation in the observed range results from nonthermal processes. Some contribution from thermal emission from dust cannot be ruled out and may explain the break in the spectra at 1 micron seen in many quasars.

Neugebauer, G.↗
NASA NTRS1979

16-39 micron spectroscopy of oxygen-rich stars

Airborne observations of the 16-39-micron spectra of 10 oxygen-rich stars with excess emission in the infrared have been obtained. The stars show excess emission attributed to circumstellar dust grains in the 16-39-micron region in the form of a broad hump peaking near 18 microns and falling smoothly to longer wavelengths. The emission is similar in character to the emission from the Trapezium region of the Orion Nebula, indicating the grain materials are quite similar in these objects. The existence of a feature in the 20-micron region is consistent with the O-Si-O bending resonance expected for silicate material. The lack of any sharp structure in the spectra indicates the silicate is in an amorphous, disordered form. A simple model of small grains of carbonaceous chondrite silicate material in a diffuse circumstellar envelope is shown to give a good qualitative fit to the observed 8-39-micron circumstellar spectra. Comparison of the observed spectra with the model spectra indicates the grain emissivity falls as the inverse square of wavelength from 20 to 40 microns.

Forrest, W. J.↗
NASA NTRS1979

Phosphine absorption in the 5-micron window of Jupiter

Since the original suggestion by Gillett et al. (1969) it has generally been assumed that the region of partial transparency near 5 micron in Jupiter's atmosphere (the 5-micron window) is bounded by the nu sub 4 NH3 at 6.1 micron and the nu sub 3 CH4 band at 3.3 micron. New measurements of Jupiter and of laboratory phosphine (PH3) samples show that PH3 is a significant contributor to the continuum opacity in the window and in fact defines its short-wavelength limit. This has important implications for the use of 5-micron observations as a means to probe the deep atmospheric structure of Jupiter. The abundance of PH3 which results from a comparison of Jovian and laboratory spectra is about 3 to 5 cm-am. This is five to eight times less than that found by Larson et al. (1977) in the same spectral region, but is in good agreement with the result of Tokunaga et al. (1979) from 10-micron observations.

Beer, R.↗
NASA NTRS1981

Water frost and ice - The near-infrared spectral reflectance 0.65-2.5 microns

The spectral reflectance of water frost and frost on ice as a function of temperature and grain size is presented with 1-1/2% spectral resolution in the 0.65- to 2.5-micron wavelength region. The well-known 2.0-, 1.65-, and 1.5-micron solid water absorption bands are precisely defined along with the little studied 1.25-micron band and the previously unidentified (in reflectance) 1.04-, 0.90-, and 0.81-micron absorption bands. The 1.5-microns band complex is quantitatively analyzed using a nonlinear least squares algorithm to resolve the band into four Gaussian components as a function of grain size and temperature. It is found that the 1.65-micron component, which was thought to be a good temperature sensor, is highly grain-size dependent and poorly suited to temperature sensing. Another Gaussian component appears to show a dependence of width on grain size while being independent of temperature. The relative apparent band depths are different for frost layers on ice than for thick layers of frost and may explain the apparent band depths seen in many planetary reflectance spectra.

Clark, R. N.↗
NASA NTRS1982

Identification of the emission features near 3.5 microns in the pre main sequence star HD 97048

The spectrum of HD97048 was measured with a resolving power of 450 between 3.37 and 3.64 microns. The prominent feature near 3.5 microns is well resolved, with a peak at 3.53 microns and a wing extending to a shorter wavelength. The weaker feature near 3.4 microns is found to peak at 3.43 microns, in contrast to the 3.40 micron feature seen in other astronomical objects. The observed spectrum strongly resembles laboratory spectra of mixtures of monomeric and dimeric formaldehyde embedded in low temperature solids. Of various possible excitation mechanisms, ultraviolet pumped infrared fluorescence of formaldehyde in interstellar grains provides the best explanation for the observed spectrum of HD 97048.

Baas, F.↗
NASA NTRS1983

The NH3 spectrum in Saturn's 5 micron window

Spectra of Saturn's 5-micron window were obtained at the Infrared Telescope Facility on Mauna Kea, Hawaii. The spectra have a resolution of 1.2/cm, and some exhibit extremely low amounts of approximately 300-micron ppt telluric H2O. The Saturn spectra show absorptions by the 2nu2 band of NH3. Long-path laboratory comparison spectra of NH3 were acquired and show considerable deviations in intensity from theoretical predictions. The calibration of Saturn's observed NH3 features with the laboratory data gives 2.0 + or - 0.5 m-amagat of NH3 using the 2nu2 Q-branch at 5.32 microns. The R(1) and R(2) lines yield an abundance about 3 times greater. Absorptions outside the range of the Q-branch can be accounted for by solid NH3 of 10-20 microns equivalent path length. The origin of Saturn's 5-micron flux is mostly thermal with some admixture of solar reflected radiation. A depletion of Saturn's NH3 abundance below the solar value is indicated, but confirmation of this conclusion will require a better understanding of the atmospheric penetration depth at 5 microns and more rigorous modeling of the spectral line formation.

Bjoraker, G. L.↗
NASA NTRS1984

The mysterious 10 micron emission feature in the spectrum of Nova Aquilae 1982

Broad-band 1.2-23 micron photometry and 1 percent resolution 7-14 micron spectrophotometry of Nova Aql 1982 are presented. This nova developed similarly to other dusty novae in that the appearance of thermal infrared emission from a circumstellar dust shell was coincident with a downward transition at visual wavelengths. A strong 10 micron emission feature appeared in the spectrum of Nova Aql 1982 during the dust shell development phase. This feature was not entirely similar to emission features previously observed in other stars with circumstellar shells. The contrast of the nova's 10 micron feature was larger than those observed in the SiC-rich shells of carbon stars. On the other hand, although the nova emission feature was reminiscent of the 10 micron silicate emission feature observed in oxygen-rich supergiants, it peaked at a slightly longer wavelength and there was no corresponding 20 micron emission feature. The contrast of the feature increased with time. It is concluded that an anomalous dust grain component, tentatively identified as SiC, nucleated and grew in the circumstellar shell of Nova Aql 1982.

Ney, E. P.↗
NASA NTRS1985

Spectroscopy of the 3 micron emission features

High-spectral-resolution observations of the 3.3 and 3.4 microns features in the three planetary nebulae NGC 7027, IC 418, and BD +30 deg 3639, in the H II region S106, and in the 'red rectangle' HD 44179 are presented. The profile of the unidentified 3.3 microns emission feature is similar in all five sources. The unidentified feature previously referred to as the 3.4 microns feature actually consists of two components, a low-level emission from 3.35 to 3.60 microns and a narrow emission peak at 3.40 microns. The strength of the latter feature relative to that of the 3.3 microns feature varies by a a factor of three from source to source. The origin and properties of these features may be explained by further development of the small-grain models of Sellgren (1984) and Leger and Puget (1984).

Geballe, T. R.↗
NASA NTRS1989

New emission features in the 11-13 micron region and their relationship to polycyclic aromatic hydrocarbons

Moderate-resolution spectra of NGC 7027, HD 44179, IRAS 2182+5050, and BD +30 deg 3639 are presented, showing that the 11.3-micron feature actually peaks at 11.22 microns. Evidence is found for new emission features near 11.9 and 12.7 microns, supporting an origin from PAHs. Also, the observed asymmetry of the 11.3-micron band is consistent with the anharmonicity expected in the C-H out-of-plane bending mode in PAHs. The analysis of the 11-13-micron emission suggests that the molecular structures of the most intensely emitting free PAHs vary between the high-excitation environment in NGC 7027 and the low-excitation but high-flux environment close to HD 44179. In addition, a series of regularly spaced features between 10 and 11 microns is detected in the spectrum of HD 44179, suggesting that a simple polyatomic hydride is present in the object's gas phase.

Witteborn, F. C.↗
NASA NTRS1989

The 10 micron spectral structure in comets

The 10 micron spectra of comets Halley (1982i), Wilson (1986l), Kohoutek (1973f) and Bradfield (1987s) are presented and compared. The silicate emission profiles of Halley and Bradfield are seen to be remarkably similar in that both contain a sharp break in the spectrum at 11.3 microns. Comet Bradfield does not show the same double peak structure seen in olivine and reported in Comet Halley be Campins and Ryan (1988) and Bregman, et al. (1987). The authors interpret the 11.3 micron signature as being due to olivine-type dust grains with at least some degree of crystallinity. Olivine alone is not enough to reproduce the shape of the 10 micron structure. However, in view of the authors' past success in fitting interstellar dust features with the emissivity profile obtained from amorphous grains produced by laser-vaporizing olivine, this is a very appealing identification. They note that there are significant variations in olivine spectra due to compositional differences, grain size distribution and related grain temperature variations to make the olivine identification tentative. They further tentatively identify the 9.8 micron feature in Halley as being due to either amorphorous olivine or a phyllosilicate (layer lattice). Neither the spectra of Halley, Kohoutek, nor Bradfield exhibited the 12.2 micron feature seen in Comet Wilson, which may prove diagnostic of the composition or thermal history differences between these comets. IR spectra of various mineral samples are discussed in terms of their match to cometary spectra.

Lynch, David K.↗
NASA NTRS1990

Comet Brorsen-Metcalf in the 3.5 micron region

Comet Brorsen-Metcalf was observed on UT 21 to 24 Aug. 1989 using the CRSP spectrometer and the 1.3 meter telescope at Kitt Peak National Observatory. The cometary continuum was detected on all nights. The data are very noisy, due to the short observation window and the untried nature of the instrument. Low resolution (0.0227 micron) spectra show the 3.4 micron C-H stretch feature having a contrast of at most a factor of two to the neighboring continuum. High resolution (0.0031 micron) spectra between 3.4 and 3.6 microns show 1 sigma features that might be attributed to the nu 5 band of formaldehyde (H2CO). Similar spectra of the region between 3.2 and 3.4 microns show one 3 sigma line at 3.34 microns, which is as yet unidentified. Although the cometary spectra were more spatially extended than the spectra of standard stars, no extension of the line emission beyond the continuum was observed.

Storrs, A. D.↗
NASA NTRS1990

High spatial resolution mapping of the Cepheus A region at 20, 50, and 100 microns

The Cepheus A region at 20 microns has been mapped, and a bright, unresolved central source with a peak flux of 41 Jy into a 4.0 arcsec x 4.3 arcsec beam has been detected. One-dimensional slit scans have been obtained in two perpendicular directions across Cepheus A at 50 and 100 microns using a high spatial-resolution sampling technique. The temperature and optical depth profile of the far-IR emission are determined, and a peak temperature of 46 K and peak 100 micron optical depth of 0.4 are derived. Maximum entropy deconvolution of the far-IR scans indicate that there is a bright central core with clumpy extended emission. Within errors the position of the 50/100 micron peak is the same as the 20-micron source; this is interpreted as indicating that the 20 micron radiation represents the short-wavelength emission from the core of the dust cloud seen in the far-IR. It is concluded that an embedded source provides the major source of luminosity in the Cepheus A region.

Ellis, H. B., Jr.↗
NASA NTRS1991

Detection of the 3.4 micron emission feature in Comets P/Brorsen-Metcalf and Okazaki-Levy-Rudenko (1989r) and an observational summary

The 3.4 micron emission feature due to cometary organics was detected in Comets P/Brorsen-Metcalf and Okazaki-Levy-Rudenko (1989r). Features-to-continuum ratios in these two comets were higher than those expected from the trend seen in other comets to date. Three micron spectra of eight comets are reviewed. The 3.4 micron band flux is better correlated with the water production rate than with the dust production rate in this sample of comets. High feature-to-continuum ratios in P/Brorsen-Metcalf and Okazaki-Levy-Rudenko can be explained by the low dust-to-gas ratios of these two comets. The observations to date are consistent with cometary organics being present in all comets (even those for which no 3.4 micron feature was evident) at comparable abundances with respect to water. The emission mechanism and absolute abundance of the organics are not well determined; either gas-phase fluorescence or thermal emission from hot grains is consistent with the heliocentric distance dependence of the 3.4 micron band flux. There is an overall similarity in the spectral profiles of the 3.4 micron feature in comets; however, there are some potentially significant differences in the details of the spectra.

Brooke, T. Y.↗
NASA NTRS1991

High-resolution spectra of the 3.29 micron interstellar emission feature - A summary

High spectral resolution observations of the 3.29-micron interstellar emission feature show two types of profiles. Type 1 has a central wavelength of 3.289-micron and is observed in extended objects such as planetary nebulae and H II regions. Type 2 has a central wavelength of 3.296 microns and is observed around a small number of stellar sources. Type 2 has a full width at half-maximum of 0.020 micron; Type 1 has a broader FWHM, perhaps as much as 0.042 micron, but this is uncertain because of contamination by Pf(delta) emission. These profiles are tabulated for comparison to laboratory data. It is found that no proposed identification for the 3.29-micron emission feature definitely matches the observational spectra, although amorphous aromatic materials and heated polycyclic aromatic hydrocarbons tend to fit the best.

Tokunaga, A. T.↗