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At least 811 records · Page 45
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NASA NTRS1985

Far-infrared and submillimeter photometry of evolved stars

Broad-band photometric observations at far infrared and submillimeter wavelengths (lambda is greater than 30 microns and less than 1) provide a unique probe of circumstellar shells in evolved objects and of the mass loss processes which produce them. The problems which these observations explore include: dust properties and dust-to-gas ratios in the outflowing material, the mass and structure of the circumstellar shell, and the pumping mechanism for maser emission. This contribution reviews the early work in this still largely unexploited field and reports results in each of the areas listed above. The dramatic advances forthcoming in this area from the IRAS satellite are previewed along with further progress which will come from the next generation of infrared and submillimeter telescopes.

Werner, M. W.↗
NASA NTRS1985

Infrared studies of the bipolar nebula OHO739

Infrared studies have been made of the M9 giant OHO739, which is embedded in a bipolar nebula, in order to study the structure and density distribution of the circumstellar disk, and preliminary results are reported. The degree of polarization across the 3.1 micron ice band in an 8 arcsec beam centered at the 2.2 micron peak is found to increase with extinction in the ice band, as expected for a bipolar scattering nebula. A distance of 2 kpc is inferred from the tilt angle of the bipolar axis and phase lag measurements of the OH maser. Maps made in the K band and in narrow bands at 2.85, 3.1, and 3.5 microns by raster-scanning OHO739 are presented. In all maps, the object is clearly elongated along the bipolar axis. Patterns of increases and decreases in extinction in the object are inferred to indicate that ice particles are widespread through the nebula and not just concentrated in the disk.

Tielens, A. G. G. M.↗
NASA NTRS1985

Radio emission from AM Herculis

Observations of the quiescent microwave emission of the magnetic cataclysmic variable AM Herculis are presented. The emission, which declined from a mean value of 0.58 mJy at 4.9 GHz to about 0.3 mJy, in rough coincidence with the entry of AM Herculis into an optical low state (mid-1983), is explained in terms of optically thick gyrosynchrotron emission. It is noted that the observation of a coherent outburst at 4.9 GHz, interpreted as the result of a cyclotron maser on the red dwarf secondary, indicates that the secondary is magnetized. Possible implications are briefly explored. Comparisons between this system and other stellar continuum radio sources are made.

Bastian, T. S.↗
NASA NTRS1986

Millisecond radio spikes from the dwarf M flare star AD Leonis

Arecibo radio observations of millisec bursts of radio signals at 1415 MHz from AD Leonis are reported. The observed burst had an ellipticity of 0.95, 50-100 percent circular polarization, and a flux density maximum of 30 mJy. The 50 sec burst featured five quasi-periodic oscillations with a mean periodicity of about 3.2 sec. A second, less intense burst that occurred 20 sec later was 100 percent circularly polarized. The area emitting the bursts covered an estimated 0.005 of the radius of AD Leonis and had an electron density of 6 billion/cu cm and a longitudinal magnetic field strength of 250 gauss, if the source was an electron-cyclotron maser. A coherent plasma source would require, for the first harmonic, an electron density of 20 billion/cu cm and a magnetic field much less than 500 gauss. A second harmonic of the plasma frequency would require an electron density of 6 billion/cu cm and a field strength much less than 250 gauss. The possibility that the source was periodic oscillations in coronal loops is discussed.

Lang, K. R.↗
NASA NTRS1986

The largest molecular cloud complexes in the first galactic quadrant

The Columbia CO survey of the first Galactic quadrant was used to determine the locations and physical properties of the largest molecular complexes in the inner Galaxy. Within the range of the survey (l = 12-60 deg), 26 complexes were detected with masses greater than 5 x 10 to the 5th solar masses, and roughly several hundred such complexes are deduced to exist throughout the Galaxy within the solar circle. These complexes are the parent objects of much of the Population I in the Galaxy. Distances to most of the complexes were determined kinematically, the distance ambiguity being resolved with the aid of associated H II regions, OB associations, masers, and other early Population I objects. The largest complexes are good tracers of spiral structure, the Sagittarius arm in particular being delineated with unprecedented clarity. A total of 17 large complexes are distributed rather uniformly along a 15 kpc stretch of the arm with a spacing comparable to that of the strings of regularly spaced H Ii regions observed in external galaxies. Power-law relations exist between the line widths and sizes of the complexes and between their densities and sizes. The forms of these relations are in good agreement with those found previously and are extended by roughly an order of magnitude in cloud mass.

Dame, T. M.↗
NASA NTRS1986

X-band preamplifier filter

A low-loss bandstop filter designed and developed for the Deep Space Network's 34-meter high-efficiency antennas is described. The filter is used for protection of the X-band traveling wave masers from the 20-kW transmitter signal. A combination of empirical and theoretical techniques was employed as well as computer simulation to verify the design before fabrication.

Manshadi, F.↗
NASA NTRS1986

Submillimetre molecular line observations of M17: The interaction of an ionisation front and molecular clouds

An area of about 9 by 10 arc minutes in the M17 molecular cloud has been mapped in the J=3-2 transition of CO. The strongest CO emission is observed to come from the two bars to the north and southwest, which lie just outside the area of ionized gas seen in the radio continuum studies. We are viewing the boundary between the ionized and molecular gas almost edge on. The most intense CO emission is from the area around the dense molecular cloud core M17SW in the southwest bar. To the east of M17SW there are signs of recent or continuing star formation including H2O masers and an ultra-compact HII region. The CO J=3-2 spectra observed are complex with considerable variation in line shapes occuring over distances of less than one arc minute. We interpret the velocity structure of this region as arising from an ensemble of molecular cloud fragments in addition to extended emission. We have identified several cloud components at different velocities within both the northern and southwest bars of CO emission. A simple kinematic model of the cloud components in the southwest bar in which they are considered to be clumps of post-shock gas lying close to the edge of the expanding HII region, with the shock being driven by Kleinmann's star, gives a velocity of approx. 10.8 km s(-1) for the expansion velocity of the HII region, which is currently at a distance of approx. 2.4 pc from Kleinmann's star. The resulting shock is thought to be preceding the ionisation front and appears to have led to the fragmentation of the original cloud.

Rainey, R.↗
NASA NTRS1986

Molecular catastrophes and the formation of circumstellar dust

Interstellar dust grains are presumed in part to have their origins in the outer atmospheres of red giant and supergiant stars because, despite the efficiency of shock destruction of grains in the interstellar medium (ISM), meteoritic samples possess isotopic signatures that are consistent with nucleosynthetic origin in the interior of evolved stars. There is ample evidence to suggest that once dust grains form near red giants and supergiants, radiation pressure is sufficient to drive them to infinity. The molecular catastrophe description for the conversion of chromospheric gas into molecular masers and circumstellar dust holds promise for a coherent explanation of the formation of these entities and the process of mas loss from cool, high luminosity objects.

Stencel, R. E.↗
NASA NTRS1986

Effects of stellar outflows on interstellar sulfur oxide chemistry

Interferometer Maps with 2" to 6" resolution of a number of regions with active star formation (Orion A, W49, W51, SGRB2) show that the distribution of the molecule SO is very compact around stellar outflow sources. Both SO and SO2 were studied near three outflows, OrionA/IRc2 and two sources in W49. The two molecules have similar distributions and abundances. More than 95% of the emission comes from regions whose extents are only .05 to .2 pc., being larger around the more energetic sources. Their spectra are broad, 30 km/sec or more, suggesting that the oxide production is associated with the flows. The outflows are identified by water masers and by extended bipolar flows in SiO. Maps in other molecules, such as HCO+ and CS, which have similar collisional excitation requirements, have much greater spatial extent. Thus it appears that the SO and SO2 abundances are truly compact and are closely associated with the outflows.

Welch, W. J.↗
NASA NTRS1986

Reference frequency transmission over optical fiber

A 100-MHz reference frequency from a hydrogen maser frequency standard has been transmitted via optical fiber over a 14-km distance with a measured stability of 1.5 X 10 to the-15 power for 1000 seconds averaging time. This capability was demonstrated in a frequency distribution experiment performed in April, 1986. The reference frequency was transmitted over a single-mode fiber-optic link from Deep Space Station (DSS) 13 to DSS 12 and back. The background leading up to the experiment and the significance of stable reference frequency distribution in the Deep Space Network (DSN) is discussed. Also described are the experiment, including the fiber-optic link, the measurement method and equipment, and finally the results of the experiment.

Lutes, G.↗
NASA NTRS1986

The R Aquarii-jet at UV and radio wavelengths

The jet and central star of the peculiar symbiotic variable R Aquarii was monitored with IUE low resolution SWP 1200 to 2000 A spectra, in order to detect possible temporal variations. The absolute line intensities of N V, C IV and He II, as well as numerous other ionic species in the jet are found to vary on a timescale of 1.5 yr. High spatial resolution radio VLA maps and SiO maser millimeter interferometer observations of the star are quoted.

Michalitsianos, A. G.↗
NASA NTRS1987

Boundary conditions for the paleoenvironment: Chemical and physical processes in the pre-solar nebula

Detailed study of the first interstellar hydrocarbon ring, cyclopropenylidene (C3H2), is continuing. The singly deuterated isotope of this molecule, C3HD, was observed in several cold interstellar clouds. The results of a large survey for C3H2 in galactic sources of various types will soon be completed. It appears that cyclopropenylidene is present in virtually all interstellar clouds of at least moderate density. In order to make the first determinations of the CO2/CO abundance ratio in interstellar sources, observations of protonated CO2 were pursued. The spectrum from 18.5 to 22 GHz for several interstellar clouds is being systematically measured. Particular attention is being given to the cold, dark clouds TMC-1 and L124N, which may be formation sites for solar mass stars. The phenomena of maser emission from molecules of methanol is being studied in certain interstellar clouds. A comparison of 1 millimeter continuum emission from dust with the column density of carbon monoxide as determined from the rare C(18)O isotope for 4 molecular clouds in the Galaxy is nearing completion. Papers published during the period of this report are listed.

Irvine, William M.↗
NASA NTRS1986

Some consequences of intense electromagnetic wave injection into space plasmas

The future possibility of actively testing the current understanding of how energetic particles may be accelerated in space or dumped from the radiation belts using intense electromagnetic energy from ground based antennas is discussed. The ground source of radiation is merely a convenience. A space station source for radiation that does not have to pass through the atmosphere and lower ionosphere, is an attractive alternative. The text is divided into two main sections addressing the possibilities of: (1) accelerating electrons to fill selected flux tubes above the Kennel-Petscheck limit for stably trapped fluxes, and (2) using an Alfven maser to cause rapid depletion of energetic protons or electrons from the radiation belts.

Burke, William J.↗
NASA NTRS1986

Relation between solar narrow-band decimeter wave bursts and associated X-ray bursts

Results are reported of an initial comparison of solar narrow-band decimeter wave spike bursts with corresponding X-ray events for 25 solar flares. Contrary to the rather straighforward temporal and spatial relations which exist between typical impulsive microwave and X-ray bursts, narrow-band decimeter wave spike bursts show complex temporal structure relative to the associated X-ray features. The time delay between the hard X-ray and microwave emission peaks varies from -2 to 8 seconds. The associated X-ray events are very weak in intensity, are spectrally very soft, and do not show any peculiar spectral features. Although the total number of bursts is small, it is found that decimeter spike bursts are 100 to 1000 times stronger than normal impulsive microwave bursts for the same observed amount of hard X-ray emission. This feature, supplemented by the fact that 100% circular polarization is observed, strongly supports a maser origin for the decimeter spike bursts.

Enome, Shinzo↗
NASA NTRS1986

The microwave spectrum of solar millisecond spikes

The microwave radiation from solar flares sometimes shows short and intensive spikes which are superimposed on the burst continuum. In order to determine the upper frequency limit of their occurrence and the circular polarization, a statistical analysis was performed on digital microwave observations from 3.2 to 92.5 GHz. Additionally, fine structures were investigated with a fast 32-channel spectrometer at 3.47 GHz. It was found that about 10 percent of the bursts show fine structures at 3.2 and 5.2 GHz, whereas none occurred above 8.4 GHz. Most of the observed spikes were very short and their bandwidth varied from below 0.5 MHz to more than 200 MHz. Simultaneous observations at two further frequencies showed no coincident spikes at the second and third harmonic. The observations can be explained by the theory of electron cyclotron masering if the observed bandwidths are determined by magnetic field inhomogeneities or if the rise times are independent of the source diameters. The latter would imply source sizes between 50 and 100 km.

Staehli, M.↗
NASA NTRS1986

Planetary radio waves

Three planets, the earth, Jupiter and Saturn are known to emit nonthermal radio waves which require coherent radiation processes. The characteristic features (frequency spectrum, polarization, occurrence probability, radiation pattern) are discussed. Radiation which is externally controlled by the solar wind is distinguished from internally controlled radiation which only originates from Jupiter. The efficiency of the externally controlled radiation is roughly the same at all three planets (5 x 10 to the -6th) suggesting that similar processes are active there. The maser radiation mechanism for the generation of the radio waves and general requirements for the mechanism which couples the power generator to the region where the radio waves are generated are briefly discussed.

Goertz, C. K.↗
NASA NTRS1986

POLYSITE - An interactive package for the selection and refinement of Landsat image training sites

A versatile multifunction package, POLYSITE, developed for Goddard's Land Analysis System, is described which simplifies the process of interactively selecting and correcting the sites used to study Landsat TM and MSS images. Image switching between the zoomed and nonzoomed image, color and shape cursor change and location display, and bit plane erase or color change, are global functions which are active at all times. Local functions possibly include manipulation of intensive study areas, new site definition, mensuration, and new image copying. The program is illustrated with the example of a full TM maser scene of metropolitan Washington, DC.

Mack, Marilyn J. P.↗
NASA NTRS1986

DE 1 observations of harmonic auroral kilometric radiation

The plasma wave instrument on board the DE 1 spacecraft has observed several intervals of auroral kilometric radiation during which harmonic structure is clearly present. The paper presents evidence, some of which is based on unique capabilities of the DE instrument, which argues strongly that the harmonic structures are natural rather than instrumental in origin. The harmonic emissions occur infrequently, but when present may persist for intervals of up to an hour. The emissions are relatively narrow band and consist of a relatively weak fundamental accompanied by an even weaker second harmonic. The ratio of power in the fundamental band to the power in the harmonic ranges from 10 to 100. In all cases, polarization data indicate that the fundamental is a left-hand ordinary (L-O) mode emission while the harmonic is right-hand extraordinary (R-X) mode. These observations are consistent with predictions based on the cyclotron maser mechanism.

Mellott, M. M.↗