Engineering topics

Geballe, T. R.

Publications and source records attributed to Geballe, T. R..

At least 55 records · Page 3

NASA NTRS1989

Spatial variations of the 3 micron emission features within nebulae

The 3 micron spectra is presented for the Orion bar region and the Red Rectangle. In both objects spectra were obtained at more than one location, corresponding to different distances from the excitation source. The well known 3.3 and 3.4 micron emission bands are seen in both objects as well as the recently discovered features at 3.46, 3.51, and 3.57 microns in the Orion bar spectra. The spectra show that the relative strengths of the 3 micron emission features vary within the Orion bar. As distance from the exciting star increases, the 3.4 and 3.51 micron features increase, and the 3.46 micron feature decreases in strength, relative to the strong 3.3 micron feature. These are two possible interpretations which are postulated, each of which involves the breaking of bonds by UV radiation, which removes the modes responsible for the 3.4 micron emission near the star. The two possible bond ruptures are the CH bond in small polycyclic aromatic hydrocarbons (PAHs), or the bond to an aliphatic subgroup. It has to be pointed out that neither interpretation appears entirely satisfactory. The vibrational overtone interpretation cannot explain the presence or behavior of the 3.46 micron feature, whereas the laboratory spectra of aliphatic sidegroups contain many more features in the 3 micron region than are observed in the astronomical sources.

Moorhouse, Alan↗

NASA NTRS1989

The infrared emission bands. II - A spatial and spectral study of the Orion bar

The 3-13 micron emission of the Orion Bar is spectroscopically and spatially studied. There are three emission components, one from 'classical' dust that accounts for the bulk of the emission longward of 20 microns, a second one from large amorphous carbon grains or polycyclic aromatic hydrocarbon (PAH) clusters accounting for the broad features, and a third from PAH molecules that accounts for the sharp bands. The 3.3 and 11.3 micron features, which are due to C-H modes, are well correlated spatially, while the 7.7 micron band, due to C=C modes, has a different distribution than the 3.3 and 11.1 micron bands. It is concluded that the sharp emission bands arise in the photodissociation transition region between the H II region and the molecular cloud and are not present in the H II region. The broad continuum feature from 11-13 microns is strong in both regions.

Bregman, J. D.↗

NASA NTRS1989

Shocked molecular hydrogen in the bipolar outflow NGC 2071

Maps of the emission from the v = 1-0 S(1) line of molecular hydrogen in the bipolar outflow of NGC 2071 are presented. The line emission is shown to peak at six positions distributed irregularly along two lobes which are parallel to, but offset about 20 arcsec from, the lobes of the high-velocity CO-line emission. The energetics and composition of the high-velocity gas support a model in which the driving agent is a bipolar atomic wind which arises from the vicinity of the central IR sources and shocks the surrounding molecular cloud, evacuating a cavity within it.

Burton, Michael G.↗

NASA NTRS1989

Spatial variations of the 3 micron emission features within UV-excited nebulae - Photochemical evolution of interstellar polycyclic aromatic hydrocarbons

Spectra at 3 microns have been obtained at several positions in the Orion Bar region and in the nebula surrounding HD 44179. Weak emission features at 3.40, 3.46, 3.51, and 3.57 microns are prominent in the Orion Bar region. The 3.40- and 3.51-micron features increase in intensity relative to the dominant 3.29-micron feature. The spectrum obtained in the Red Rectangle region 5 arcsecs north of HD 44179 are similar to those in the Orion Bar, with a weak, broad 3.40-micron feature at the position of HD 44179. The spatial behavior of the weak emission features is explained in terms of hot bands of the CH stretch and overtones, and combination bands of other fundamental vibrations in simple PAHs. Based on the susceptibility of PAHs to destruction by the far UV fields in both regions, PAH sizes are estimated at 20-50 carbon atoms.

Geballe, T. R.↗

NASA NTRS1989

An infrared study of starbursts in the interacting galaxy pair Arp 299 (NGC 3690+IC 694)

Extensive infrared observations have been obtained of the three active regions in Arp 299. Multiaperture JHK photometry reveals that the colors of the three regions are totally different from each other, and that there are very red nuclei smaller than 4 arcsec in two of them. Multiaperture spectroscopy of the Br-gamma and the shock-excited H2 lines shows that both the atomic and molecular lines are spatially extended, indicating that Arp 299 is undergoing an active episode of star formation not only in its nuclei but also well outside of them. Although there is some evidence that suggests the presence of a compact, active galactic nucleus, a simple starburst model can explain the bolometric luminosities, production rates of ionizing photons, and H24 line luminosities of each active region in Arp 299. However, each starburst cannot last longer than 10 to the 8th yr.

Nakagawa, Takao↗

NASA NTRS1989

Arsine in Saturn and Jupiter

New spectra of Saturn and Jupiter are reported that show a prominent, heretofore unidentified absorption near 2126/cm. The observation is interpreted as unambiguous evidence for the presence of arsine, AsH3. The abundance of AsH3 appears to be almost a factor of two higher in Saturn than in Jupiter. The observed enrichments are consistent with the core instability model for the formation of giant planets. Models of arsenic chemistry that predict strong depletions of AsH3 at temperatures below 370 K are not consistent with the observations, suggesting that vertical convection or perhaps some other mechanism inhibits depletion. Arsenic is the first new element identified in a planetary atmosphere since germanium was found in Jupiter a decade ago.

Noll, Keith S.↗

NASA NTRS1989

The constancy of the ratio of the molecular hydrogen lines at 3.8 microns in Orion

The 1-0 O(7) and 0-0 S(13) lines of H2, at 3.807 and 3.846 microns, have been mapped over the region of the Orion molecular outflow. The intensity ratio of these lines is found to be independent of position in the outflow. From this it is inferred that the structure of the shocks and their cooling flows in Orion may be more akin to hydrodynamic shocks than the low-temperature C-shocks that are currently favored.

Brand, P. W. J. L.↗

NASA NTRS1989

Molecular hydrogen line ratios in four regions of shock-excited gas

Five emission lines of molecular hydrogen, with wavelengths in the ranges of 2.10-2.25 and 3.80-3.85 microns, have been observed in four objects of different type in which the line emission is believed to be excited by shocks. The relative intensities of the lines 1 - 0 S(1):1 - 0 S(O):2 - 1 S(1) are approximately 10.5:2.5:1.0 in all four objects. The 0 - 0 S(13):1 - 0 O(7) line ratio, however, varies from 1.05 in OMC-1 to about 2.3 in the Herbig-Haro object HH 7. The excitation temperature derived from the S(13) and O(7) lines is higher than that derived from the 1 - 0 and 2 - 1 S(1) lines in all four objects, so the shocked gas in these objects cannot be characterized by a single temperature. The constancy of the (1-0)/(2-1) S(1) line ratio between sources suggests that the post-shock gas is 'thermalized' in each source. The S(13)/O(7) ratio is particularly sensitive to the density and temperature conditions in the gas.

Burton, M. G.↗

NASA NTRS1988

Ratios of molecular hydrogen line intensities in shocked gas - Evidence for cooling zones

Column densities of molecular hydrogen have been calculated from 19 infrared vibration-rotation and pure rotational line intensities measured at peak 1 of the Orion molecular outflow. The run of column density with energy level is similar to a simple coolng zone model of the line-emitting region, but is not well fitted by predictions of C-shock models current in the literature.

Brand, P. W. J. L.↗

NASA NTRS1988

Evidence for germane in Saturn

Observations in Saturn have prompted the development of an 0.4 + or - 0.2 ppb mole fraction for germane (GeH4) on the basis of the P- and R-branch lines' spectra. The presence of germane in Saturn implies a disequilibrium of the upper atmosphere by rapid vertical convection. It is suggested that future, more realistic radiative transfer models that include the effects of scattering within a cloud layer will probably only reduce the mole fraction presently derived for germane, by increasing the effective path length in a given atmospheric layer.

Noll, Keith S.↗

NASA NTRS1988

The ice band in IRAS 09371 + 1212

Spectra from 2 to 4 microns of the unusual IRAS source 09371 + 1212, a bipolar nebula, reveal a deep H2O ice absorption band near 3.1 microns. No long-wavelength wing is present, implying that the absorbing grain mantles are of high purity. The structure of the absorption feature is reasonably well modeled by a mixture of amorphous and crystalline H2O ice mantles on silicate grains, but discrepancies remain that could indicate other absorbers also.

Geballe, T. R.↗

NASA NTRS1988

The origin and vertical distribution of carbon monoxide in Jupiter

Six clearly-resolved lines of the CO 1-0 vibration-rotation band near 4.7 microns have been observed in Jupiter at a resolution of 0.07/cm. CO is not found to be concentrated in the stratosphere, but is shown to be present in the troposphere at a mole fraction of 1.6 + or - 0.3 x 10 to the -9th, suggesting that rapid vertical mixing is the source of CO. Results indicate that the global oxygen abundance in Jupiter's gaseous envelope below the cloud-forming regions must be near the solar value, and that intervening clouds with an optical depth of 0.5-4 are present above the line-forming region.

Noll, Keith S.↗

NASA NTRS1988

Spatial variations of the 3-micron emission features within Orion's Bar

3-micron spectra of the Orion Bar region have been obtained at three positions corresponding to different distances from the exciting source. The recently discovered unidentified features at 3.46, 3.51, and 3.57 microns are clearly visible. The spectra show that the 3.4 and 3.51-micron emission features increase in intensity relative to the strong 3.3-micron feature as the distance from the exciting source increases. The implications for polycyclic aromatic hydrocarbons and recent ideas concerning their ultraviolet excitation and spatial evolution are discussed.

Moorhouse, A.↗

NASA NTRS1986

Ground-based detection of water in Comet Halley

Gaseous water was detected in the coma of comet Halley. Emission was observed in the upsilon 1 + upsilon 3 band at 1.4 microns, and the upsilon 2 + upsilon 3 band at 1.9 microns. Based on the upsilon 1 + upsilon 3 band intensity, the mass loss rate is 2 times 10 to the 29th power molecules/sec (with an uncertainty of a factor of 2) on 29 Oct. 1985, marginally consistent with other detections. The method is applicable to observations of H2O in other fast-moving comets.

Knacke, R. F.↗

NASA NTRS1986

Detection of carbon monoxide in Saturn

The detection of CO in the atmosphere of Saturn is reported. Six spectral regions containing lines of the CO 1-0 vibration-rotation band near 4.7 microns are studied; three of the lines are free of blending and in effect attest to the presence of this molecule in Saturn's atmosphere. Consideration is given to the following CO sources: (1) rapid convection from the hot interior, and (2) the infall of oxygen-bearing material from outside.

Noll, Keith S.↗

NASA NTRS1986

Some recent infrared spectroscopy of interstellar processes

The potential which infrared spectroscopic techniques provide for studying interstellar process is demonstrated. Several examples are given. The data were obtained at UKIRT, using its frequency-chopped Fabry-Perot spectrometer and its seven-channel cooled grating spectrometer.

Geballe, T. R.↗

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 NTRS1984

NGC 2024: Multi-wavelength Infrared and Radio Observations

A series of far-infrared maps obtained on the KAO find the total IR luminosity of NGC 2024 is to the 4th power L, and show a peak in flux density and optical depth about 1' south of IRS 2. High resolution spectra of IRS 2 in Brackett alfa and Pfund gamma indicate the presence of an optically thick wind with M approx. 7 x 10 to the minus 7 power M sub yr to minus 1 power, from which we infer that IRS 2 is unable to supply the luminosity observed. A six centimeter continuum map peaks near the location of the far-infrared peak and confirms it as a likely site for a source to provide this luminosity. Maps in HCN, CS, and H2CO show the gas is dense in the direction of the far IR peak. Velocity analysis shows the H2 region created by the far IR source and IRS 2 forms an expanding bubble in front of which the H2CO is seen in absorption, and which is bounded in the south and behind by dense material.

Smith, H. A.↗