Engineering topics

Russell, Ray W.

Publications and source records attributed to Russell, Ray W..

31 records · Page 2

NASA NTRS1992

8-13 micron spectroscopy and IR photometry of Comet P/Brorsen-Metcalf (1989o) near perihelion

Thermal IR spectrophotometry of Comet P/Brorsen-Metcalf near perihelion was obtained during August 28-September 6, 1989, by the NASA IRTF; these data are presently compared with results for Comet P/Halley. The spectra, which lacked silicate emission, are consistent with 400-430 K grey body emission. The grains are on these bases inferred to have been larger than typical for either new comets or P/Halley. Attention is given to the composition, mass, temperature, and character of the cometary dust in view of Comet P/Halley study results.

Lynch, David K.↗

NASA NTRS1990

Comparison of P/Brorsen-Metcalf and P/Halley in the thermal infrared

Of the periodic comets, only comets Halley and Brorsen-Metcalf have periods of the order of 75 years and are bright enough to study spectroscopically in the infrared. Thermal IR spectroscopy of comet P/Brorsen-Metcalf near perihelion are presented and the results are compared to comet P/Halley.

Lynch, David K.↗

NASA NTRS1990

Silicates and variability in comets Okazaki-Levy-Rudenko (1989r) and Austin (1989c1)

Comet Okazaki-Levy-Rudenko (1989r) was studied over a wide range of wavelengths from the UV to the submillimeter. Using visual magnitude estimates from the IAU Circulars and reported submillimeter fluxes in conjunction with the thermal infrared spectroscopy and filter photometry, the nature of the grains and the behavior of the comet can be assessed and compared to other comets studied under this program. In addition, preliminary results from a collaborative infrared study of Comet Austin are presented which address the nature of the dust in that comet. Progress on a model for cometary properties and brightness behavior is discussed.

Russell, Ray W.↗

NASA NTRS1989

Si3N4 emissivity and the unidentified infrared bands

Infrared spectroscopy of warm (about 150 to 750 K), dusty astronomical sources has revealed a structured emission spectrum which can be diagnostic of the composition, temperature, and in some cases, even size and shape of the grains giving rise to the observed emission. The identifications of silicate emission in oxygen rich objects and SiC in carbon rich object are two examples of this type of analysis. Cometary spectra at moderate resolution have similarly revealed silicate emission, tying together interstellar and interplanetary dust. However, Goebel has pointed out that some astronomical sources appear to contain a different type of dust which results in a qualitatively different spectral shape in the 8 to 13 micron region. The spectra shown make it appear unlikely that silicon nitride can be identified as the source of the 8 to 13 micron emission in either NGC 6572 or Nova Aql 1982. The similarity between the general wavelength and shape of the 10 micron emission from some silicates and that from the two forms of silicon nitride reported could allow a mix of cosmic grains which include some silicon nitride if only the 8 to 13 micron data are considered.

Russell, Ray W.↗

NASA NTRS1989

Observational constraints on interstellar dust models

No single model has been able to account for all of the observed spectroscopic properties of interstellar or circumstellar dust. The reason for this is that, despite the agreement that the grains are composed of silicaceous/metal oxide and carbonaceous material, there is strong disagreement as to their exact structure and composition. This led Draine and Lee (1984) to use interstellar extinction data to define an interstellar graphitic material; new observational findings have made even that identification uncertain. But the great advantage of their approach is that they used observations at all of the wavelengths available to define the material. Here, the authors attempt a variation of that approach. They examine recent UV and IR data and attempt to put constraints on the possible types of interstellar grain composition, and to connect these constraints with grain models. A summary of some of the important constraints imposed by the observations is given.

Hecht, James H.↗

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 NTRS1988

Laboratory investigations

Laboratory studies related to cometary grains and the nuclei of comets can be broken down into three areas which relate to understanding the spectral properties, the formation mechanisms, and the evolution of grains and nuclei: (1) Spectral studies to be used in the interpretation of cometary spectra; (2) Sample preparation experiments which may shed light on the physical nature and history of cometary grains and nuclei by exploring the effects on grain emissivities resulting from the ways in which the samples are created; and (3) Grain processing experiments which should provide insight on the interaction of cometary grains with the environment in the immediate vicinity of the cometary nucleus as the comet travels from the Oort cloud through perihelion, and perhaps even suggestions regarding the relationship between interstellar grains and cometary matter. A summary is presented with a different view of lab experiments than is found in the literature, concentrating on measurement techniques and sample preparations especially relevant to cometary dust.

Russell, Ray W.↗

NASA NTRS1988

Comet Halley's colorful outbursts

Two preperihelion outbursts by Comet Halley were observed, each showing different brightness changes at 2.3, 3.6, 4.6 and 10.3 micrometers. Neither event was observed from beginning to end. The first observation on 8 Nov. 1985 lasted on the order of a day and was accompanied by a tail-like appendage recorded photographically. During the outburst the IR colors changed dramatically, showing no significant change at 10.3 micrometers but showing progressively more change at shorter wavelengths over a time scale of a few hours. The second outburst measurement extended over several days (10 to 13 Jan. 1986) during which time the intensities at the four wavelengths increased by roughly the same amount. Although the outbursts were of different duration, the IR measurements suggest that the first event involved volatile ice particles that evaporated, while the second was associated with long lived nonvolatile dust grains.

Lynch, David K.↗

NASA NTRS1988

Some 5-13 micrometer airborne observations of Comet Wilson 1986l: Preliminary results

Comet Wilson was observed from the Kuiper Airborne Observatory approximately 23.6 and 25.7 Apr. 1987, UT (approx. 3 to 5 days after perihelion) using the NASA-Ames Faint Object Grating Spectrometer. Spectrophotometric data were observed with a 21 inch aperture between 5 and 13 micrometer and with a spectral resolution of 50 to 100. Spectra of the inner coma and nucleus reveal a fairly smooth continuum with little evidence of silicate emission. The 5 to 8 micrometer color temperature of the comet was 300 + or - 15 K, approx. 15 percent higher than the equilibrium blackbody temperature. All three spectra of the nucleus show a new emission feature at approx. 12.25 micrometer approx. two channels (.22 micrometer) wide. Visual and photographic observations made during the time of these observations showed a broad faint, possible two component tail. No outburst activity was observed.

Lynch, David K.↗

NASA NTRS1987

Airborne spectrophotometry of Eta Carinae from 4.5 to 7.5 microns and a model for source morphology

Spectrophotometric observations of Eta Car between 4.5 and 7.5 microns show a featureless thermal-like spectrum with no fine-structure lines or broad emission or absorption features. The color temperature of the spectrum is approximately 375 K. High spatial resolution maps at 3.5, 4.8, and 10 microns obtained from the ground are used to discuss the dust distribution and temperature structure, and to present a model for general source morphology. The upper limit to the brightness of the forbidden Ar II fine-structure emission line at 6.98 microns is less than 7 x 10 to the -16th W/sq cm, which still allows for a significant overabundance of argon and is consistent with the evolved nature of the source.

Russell, Ray W.↗

NASA NTRS1987

One-micron CN observations of Comet Halley

Three spectra of Comet Halley in the 0.86 to 1.37-micron wavelength region have been obtained. On December 4, 1985, the 0-0, 1-1, 1-0, and 2-1 transitions of the red system of CN were detected using a 13 arcsec aperture centered on the nucleus of the comet. The 0-0 and 1-1 transitions were also observed in the coma at positions 20 arcsec from the nucleus. A line to continuum ratio of 0.25 was observed for the 0-0 transition at the position of the nucleus of the comet. A ratio of 1.5 was observed at the off-nucleus positions. On April 28, 1986, an upper limit to the strength of the 0-0 transition was obtained.

Rossano, George S.↗

NASA NTRS1986

Pre-perihelion observations of Comet Halley at 2-13 microns

Between Nov. 8, 1985 and Jan. 13, 1986 comet Halley brightness was obtained as a function of time at 2.3, 3.6, 4.6, and 10.3 microns. Brightness outbursts were noted, an especially significant one beginning Jan. 10, 1986 and persisting for several days during which the IR brightness more than doubled. The heliocentric brightness indices for 2.3, 3.6, 4.6, and 10.3 microns are -5.7, -7.1, -8.5, and -6.2, respectively. Comet Halley's absolute magnitudes at these wavelengths are 7.3, 4.4, 2.8, and -1.8. The 4.6 to 10.3 micron color temperature dependence on heliocentric distance (R) is slightly less steep than the Rsup -1/2 expected theoretically. The albedo of the comet is 8% to 9%. Based on spectral differences between outbursts on Nov. 8, 1985 and Jan. 10 to 13, 1986, it is concluded that the comet displays composition inhomogeneities.

Lynch, David K.↗

NASA NTRS1981

Giant [C II] Halos Around H II Regions

We have mapped the submillimeter (157 mu.m) [C II] emission from the M17 complex. The [C II] emission extends over at least 1/4 deg in the sky. The regions emitting the C II radio recombination lines contribute only in a minor way to the total 157 mu.m [C II] flux. The total [C II] luminosity of M17 exceeds 2 x 10(exp 3) solar luminosity.

Russell, Ray W.↗