Engineering topics

Tokunaga, A. T.

Publications and source records attributed to Tokunaga, A. T..

At least 55 records · Page 3

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

Small-aperture infrared photometry of Seyfert 1 galactic nuclei

Multiaperture infrared photometry of the nuclei of five Seyfert 1 galaxies is presented. When apertures approaching the seeing limit were used, it was found that all of the nuclei have observed power law energy distributions with F(nu) proportional to 1/nu sq from 1.25 to 3.45 micron. After correcting for reddening, the spectral indices had a range of alpha = 1.4-1.9. These results are supported through infrared imaging of one of the program galaxies, and they demonstrate the importance of properly isolating the nuclear component from the stellar disk through the use of extremely small apertures. Although the nature of the infrared emissions cannot be determined, results indicate that a common energy source exists among the observed galaxies.

Simons, D. A.↗

NASA NTRS1988

High spectral resolution observations of HD 44179 at 3.2-3.7 microns

New high-resolution spectra of HD 44179 (the 'Red rectangle') in the 3.2-3.7 micron range are presented. Contrary to previous observations, no evidence is found for the 3.4 micron feature which is supposed to arise from aromatic hydrocarbons. The strong 3.29 micron feature is found to be different from that seen in NGC 7027 and IRAS 21282+5050.

Tokunaga, A. T.↗

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 NTRS1987

Detection of a new emission band at 2.8 microns in Comet P/Halley

A 2.8- to 3.7-micron spectrum of Comet Halley taken in May 1986 is presented. The spectrum shows the 3.36-micron emission feature that most likely arises from carbonaceous material and a previously unknown emission band at 2.8-2.9 microns with no evidence for the 3-micron water-ice band either in reflection or absorption. The 2.8- to 2.9-micron emission feature does not arise from infrared fluorescence from water or OH. Since LTE emission from water is unlikely, the nature of this feature is uncertain.

Tokunaga, A. T.↗

NASA NTRS1987

Infrared emission from P/Halley's dust coma during March 1986

Photometry at 2-20 microns of the inner dust coma of comet Halley was obtained at the NASA IRTF on March 6.85, 12.8, 13.75, 17.7, and 24.8. Positions offset 10 arcsec were measured as well as the central brightness. The strength of the 10 micron emission feature was observed to vary with location in the coma. The infrared emission is in general agreement with the dust size distribution measured from the Vega and Giotto spacecraft. March 6.8, 17.7, and 24.8 corresponded to strong dust jet activity. The strength of the 10 micron silicate emission is shown to be a sensitive indicator of grain size and thus of jet activity. Dust production rate on March 13.75, 6 hr before Giotto encounter, was about 10 to the 7th gm/s.

Hanner, M. S.↗

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

The NASA infrared telescope facility Comet Halley monitoring program. I - Preperihelion results

The 1-20 microns IR monitoring program for Comet Halley whose results are presented covered January 1985 to January 1986, using a 7-arcsec aperture. It is noted that the comet's dust production was about 6 million g/s at a heliocentric distance of 1 AU; the albedo of the dust in the coma was 3-4 percent. These results are compared with those for previously observed comets.

Tokunaga, A. T.↗

NASA NTRS1986

3 micron spectroscopy of comet Halley (1982i)

Near-infrared spectroscopy and photometry was obtained of comet Halley in December 1985 when its heliocentric distance was 1.19 AU. No water ice absorption or molecular band emission were observed. The interstellar 3.3-micron emission band was also not observed. The 3-micron spectrum of comet Halley consisted of scattered sunlight at wavelengths less than 3.1 microns and of thermal emission by dust at longer wavelengths.

Tokunaga, A. T.↗

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

More interstellar emission features at 3.3-3.6 micrometers!

The present data set consists of 3.20 to 3.55 micron spectra of HD44179, NGC 7027, BD+30 3639, and Elias 1 obtained with a cooled-grating array spectrometer (CGAS) at the NASA Infrared Telescope Facility. Emission features and details of the emission feature profiles are presented for high resolution spectra. Greater complexity is shown than might be expected. It is significant that the 3.29 micron feature has an invariant central wavelength, even at high resolution, and this strongly supports the case for a very specific substance or mixture of substances which is giving rise to this feature.

Tokunaga, A. T.↗

NASA NTRS1986

Moderate spectral resolution observations of 3 micron absorption features in highly obscured objects

The 3 micron absorption spectra of sources seen in or behind molecular clouds generally show a variety of absorption features. Three separate absorptions are used to explain these features. The cooled-grating array spectrometer (CGAS) at the NASA Infrared Telescope Facility was used to obtain spectra of the late-type mass-loss star OH 0739-12 and the protostars MonR2 IRS-2 and IRS-3 (solid circles). The differences between the spectra are discussed.

Smith, R. G.↗

NASA NTRS1986

The abundances of ethane to acetylene in the atmospheres of Jupiter and Saturn

The present determination of the stratospheric abundances of ethane and acetylene on Jupiter and Saturn on the basis of IR spectra near 780/cm uses atmospheric models whose thermal and density profiles have constant mixing ratios. The ratio of ethane to acetylene is noted to be insensitive to model atmosphere assumptions; it is 55 + or - 31 for Jupiter and 23 + or - 12 where model mixing ratios are uniform. Atmospheric model density profiles adapted from theoretical photochemical models are noted to also yield a higher ethane/acetylene ratios for Jupiter.

Noll, K. S.↗

NASA NTRS1986

The distribution of dust in the inner coma of comet IRAS-Araki-Alcock (1983d)

The behavior and characteristics of the inner coma of the Comet IRAS-Araki-Alcock (IAA) were examined for five nights in May 1983 using a ground-based 2.2 m CCD telescope. A highly variable, asymmetric sunward emission was detected, along with a long filamentary structure. The brightness was highest in the sunward direction, with radial brightnesses diminishing more slowly than predicted with a 1/r model. The slow fall-off is attributed to the emission of conglomerate dust grains which fragment while traveling through the inner coma and increase the effective surface area of the dust. Significant day-to-day variations were observed, and the filamentary features were indicative of a centralized region on a mantled nucleus which rotated. The nucleus is estimated to be no more than 17 km in diameter.

Storrs, A. D.↗

NASA NTRS1986

The abundances of ethane and acetylene in the atmospheres of Jupiter and Saturn

Noll, K. S.↗

NASA NTRS1986

A faint object spectrometer for the infrared

A cryogenic astronomical spectrometer for the NASA Infrared Telescope Facility is described. This spectrometer will employ an array of at least 20 detectors and provide a resolving power of 100 to 1500 at 1-5 microns. The resolving power will be adjustable by changing gratings.

Tokunaga, A. T.↗

NASA NTRS1985

Dark grains in comet Crommelin

Comet P/Crommelin (1983n) was observed at 1-20 microns at the NASA IRTF March 29-April 1, 1984. The thermal emission spectrum fits a black body of about 290 K, cooler than other comets observed at 1 AU. The ratio of thermal to scattered radiation indicates that these grains were extremely dark with a geometric albedo of about 0.015 at J(1.25 microns) and 0.02 at K(2.25 microns). The 10 micron flux distribution on April 1 was very asymmetric, decreasing rapidly on the sunward side, less than 6000 km from the nucleus, and extended in the north and east. The spatial distribution and photometric data suggest that large grains emitted from the nucleus at very low velocity were viewed.

Hanner, M. S.↗

NASA NTRS1985

The dust coma of periodic Comet Churyumov-Gerasimenko (1982 VIII)

IR emission from the dust comet of Comet C-G was monitored at 1-20 microns with the 3-m NASA Infrared Telescope Facility at Mauna Kea, Hawaii during its perihelion passage from September 1982 to March 1983. The maximum dust production rate of approximately 200,000 g/sec was found to occur approximately one month after perihelion. It was also found that no obvious 1-micron silicate feature was present at 1.33 AU preperihelion, and that the ratio of dust/gas production was higher in other short-period comets observed in the infrared, particularly preperihelion. The low albedos derived for the dust grains (less than 0.05 micron) are noted to be plausible for mineral mixtures expected in cometary grains.

Hanner, M. S.↗