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Krishna Swamy, K. S.

Publications and source records attributed to Krishna Swamy, K. S..

At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Infrared emission from comets

IR observations of seven comets from 4 to 20 microns are discussed. It is found that the IR emission depends primarily on the comet's heliocentric distance. A model is applied to the observations based on grain populations composed of a mixture of silicate and amorphous carbon particles in the mass ratio of about 40 to 1, with a power-law size distribution similar to that inferred for Comet Halley. The results suggest that the 3.4-micron feature observed in Comet Halley is primarily due to thermal emission from the comet dust when the comet is close to the sun. It is found that the emission curve from about 4 to 8 microns provides the best spectral region for estimating the cometary grain temperature distribution.

Krishna Swamy, K. S.↗
NASA NTRS1988

Resonance fluorescence calculations for some sulphur diatomics in comets

Statistical equilibrium calculations have been carried out for S2 which was detected in Comet IRAS-Araki-Alcock and for SO, SH and CS+ which are likely to be present in the cometary comas. In all cases, a pattern of features of similar intensity is predicted - so that identifications are possible even when signal : noise is poor and other emissions interfere. These results can guide searches and help confirm the presence of these features in cometary spectra.

Krishna Swamy, K. S.↗
NASA NTRS1987

Some diatomic molecules from comet P/Halley's UV spectra near spacecraft flybys

The abundances of diatomic molecules seen in the UV both give clues to the parent compounds and help unravel the gas and ion mass spectrometry. From IUE spectra of comet Halley, upper limits on SH and CS(+) column densities and estimates of probable NO, S2, and SO are found. In particular, judged from the 226-nm gamma band, NO was relatively abundant at 2-8 x 10 to the 13th/sq cm on March 9-14. The production rate of S2 was around 1 x 10 to the 27th molecules/s at that time, but both showed day-to-day variability by 2-3 times.

Wallis, Max K.↗
NASA NTRS1987

Study of the isotopic features of Swan bands in comets

It is shown from a detailed statistical equilibrium calculation of the (C-12)(C-13) molecule that the interpretation of the observed intensities of Swan bands of the normal and the isotopic molecule of C2 in terms of the abundance ratio of C-12 and C-13 is a reasonable one. The synthetic profile of some isotopic features in the (0.0) Swan band is compared with the observed profiles for comet West.

Krishna Swamy, K. S.↗
NASA NTRS1987

Sulphur compounds in cometary IUE spectra

From a study of cometary IUE spectra, a tentative identification of bands of the B-X systems of the SO molecule in the comet IRAS-Araki-Alcock in the 2200-2400 A region is reported, and it is suggested that sulphur compounds are more prevalent in comets than has been previously realized. S(+) and possibly SH are evident in comet Halley spectra, and new bands in the (A-X) system of CS and the (B-X) system of S2 are identified. The present results throw doubts on previous assessments of dust abundances from scattered continua in the 2900-3000 A region. The relatively strong abundance of S2 compared to OH in the Cernis and Bowell comets suggests that S2 is not well mixed and is not bound in H2O-ice.

Krishna Swamy, K. S.↗
NASA NTRS1987

Statistical equilibrium in cometary C2. IV - A 10 level model including singlet-triplet transitions

Resonance fluorescence theory was used to calculate the population distribution in the energy states of the C2 molecule in comets. Ten electronic states, each with 14 vibrational states, were used in the calculations. These new calculations differ from earlier work in terms of additional electronic levels and the role of singlet-triplet transitions between the b and X levels. Since transition moments are not known, calculations are made of observable flux ratios for an array of possible values. Comparison with existing observations indicates that the a-X transition is very important, and there is marginal indication that the b-X transition is present. Swan band sequence flux ratios at large heliocentric distance are needed, as are accurate Mulliken/Swan and Phillips/Ballik-Ramsay (1963) observations.

Krishna Swamy, K. S.↗
NASA NTRS1984

The detection of the 5577.3 A forbidden line of O I in comets

The spectral synthesis of C2 Swan band sequence Delta V = -1 indicates the intensity of the forbidden green oxygen line of 5577.3 A to be about 3 to 5 percent of the 6300 A line. Therefore, it appears that the green line should be observable in high-resolution spectra of a bright comet. Festou and Feldman suggest red/green greater than or equal to 10 means a water parent origin.

Krishna Swamy, K. S.↗
NASA NTRS1982

Molecules in celestial objects. III - Study of CO in interstellar diffuse clouds

The absorption lines corresponding to the A-X transition of CO have been looked for in the IUE spectra of 14 stars with varying values of the colour excess, E(B-V) and found to be present in the spectra of nine stars with E(B-V) at least 0.28. The column density of CO has been determined towards these nine stars and its upper limit towards the rest of the stars. The curve of growth analysis has been found to show that the contribution to CO absorption is possibly from a single interstellar cloud for stars with E(B-V) less than 0.4 and from more than one cloud for stars with E(B-V) greater than 0.4. The observed column density of CO as a function of E(B-V) has been found to be in good agreement with that expected from the theory of ion-molecular chemistry.

Tarafdar, S. P.↗
NASA NTRS1978

An interstellar cloud density from Copernicus observations of CO in the spectrum of Zeta Ophiuchi

Interstellar CO absorption bands in Copernicus spectra of Zeta Oph have been studied. Absorption profiles, computed under the assumption that excitation is due to collisions with H2 molecules and interaction with the 3-K background radiation field, were fitted to the reduced data of nine bands. When a gas kinetic temperature of 56 K is assumed, the best-fit condition implies a hydrogen-nucleus density of 120 per cu cm, a CO column density of 1.2 by 10 to the 15th power per sq cm, and a radial-velocity dispersion of 0.9 km/s. The relevance of these results to existing ideas concerning the Zeta Oph interstellar clouds is discussed. It is suggested that the strongest interstellar component is not circumstellar in origin but is instead part of a supernova remnant. Simple calculations are made to establish the plausibility of the supernova-remnant identification. This suggestion is also supported by Heiles's (1976) 21-cm pictures.

Smith, A. M.↗