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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 757 records · Page 42
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NASA NTRS1986

Jet activity in the symbiotic variable R Aquarii

Low-resolution ultraviolet spectra of the R Aquarii jet have been obtained with the International Ultraviolet Explorer (IUE). The most recent IUE observations indicate the ionization state of the jet is increasing. Subarcsecond, Very Large Array observations of R Aquarii have resolved the radio-continuum structure into discrete parcels of emission that are extended and nearly collinear. R Aquarii provides evidence that indicates stellar jet activity is not unique to objects associated with high-energy emission processes alone. Rather, the nature of the aligned radio-optical features that comprise the R Aquarii jet indicate that directional mass expulsion, in the form of discrete-collimated ejecta, probably reflect a general, underlying, physical process associated with a wide variety of peculiar stellar objects. As such, the R Aquarii jet constitutes a prototype for jet activity in composite or peculiar emission stars.

Michalitsianos, A. G.↗
NASA NTRS1986

Chromospheric activity of cool giant stars

During the seventh year of IUE twenty-six spectra of seventeen cool giant stars ranging in spectral type from K3 thru M6 were obtained. Together with spectra of fifteen stars observed during the sixth year of IUE, these low-resolution spectra have been used to: (1) examine chromospheric activity in the program stars and late type giants in general, and (2) evaluate the extent to which nonradiative heating affects the upper levels of cool giant photospheres. The stars observed in this study all have well determined TiO band strengths, angular diameters (determined from lunar occulations), bolometric fluxes, and effective temperatures. Chromospheric activity can therefore be related to effective temperatures providing a clearer picture of activity among cool giant stars than previously available. The stars observed are listed.

Steiman-Cameron, T. Y.↗
NASA NTRS1986

The shapes of the circumstellar silicate features

Around oxygen-rich stars the spectra of most long-period variables (LPV) show an excess infrared emission which is attributed to circumstellar silicate dust grains. It is known that the spectral energy distribution of the 10 micron emissions shows variations from star to star. With the availability of many Infrared Astronomy Satellite (IRAS) Low Resolution Spectra (LRS) in the 8 to 22 micron region, the 10 micron feature can be studied to determine its uniformity (or lack thereof). The excess silicate emissions (10 micron emission), divided into three groups characterized by similar spectral shapes, are discussed.

Little-Marenin, I. R.↗
NASA NTRS1986

Ultraviolet spectra of the N-type carbon star TX Piscium

Nine IUE low resolution spectra of TX Psc, one of the brightest N-type carbon stars, were analyzed. The integrated flux of the Mg II (UV 1) line (blend of h and k) varies by a factor of 7, and the flux of other lines varies similarly and in phase. No variations greater than a factor of 2 occur in the continuous flux. Synthetic spectra from a model chromosphere show surprisingly good agreement with the IUE observations. The enormous influence of the wings of the Mg I resonance line is noted, suggesting it may be a major part of the well-known violet and ultraviolet opacity in cool carbon stars.

Johnson, Hollis R.↗
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 NTRS1986

Diagnostics and structure

The structure of prominences and the diagnostic techniques used to evaluate their physical parameters are discussed. These include electron temperature, various densities (n sub p, n sub e, n sub l), ionization degree, velocities, and magnetic field vector. UV and radio measurements have already evidenced the existence of different temperature regions, corresponding to different geometrical locations, e.g., the so called Prominence-Corona (P-C) interface. Velocity measurements are important for considering formation and mass balance of prominences but there are conflicting velocity measurements which have led to the basic question: what structure is actually observed at a given wavelength; what averaging is performed within the projected slit area during the exposure time? In optically thick lines, the question of the formation region of the radiation along the line of sight is also not a trivial one. The same is true for low resolution measurements of the magnetic field. Coupling diagnostics with structure is now a general preoccupation.

Vial, J. C.↗
NASA NTRS1987

The control network of Mars: October 1986

The control network of Mars is composed of Mariner 9 frames which essentially give full coverage of the planet at low resolution. Superimposed on and tied to this network are strips of Viking mapping frames (resolution 100 to 250 m per pixel) which encircle the equator and 60 deg north latitude and multiple longitude ties between these latitude strips. There are multiple ties between these strips and the Viking 1 lander site. In the future another strip will be established at 60 deg south latitude. Because the Viking 1 lander site has been accurately located, the coordinates of points in its vicinity can be determined with an error of less than 100 m relative to an inertial coordinate system.

Davies, Merton E.↗
NASA NTRS1987

The Mars observer camera

A camera designed to operate under the extreme constraints of the Mars Observer Mission was selected by NASA in April, 1986. Contingent upon final confirmation in mid-November, the Mars Observer Camera (MOC) will begin acquiring images of the surface and atmosphere of Mars in September-October 1991. The MOC incorporates both a wide angle system for low resolution global monitoring and intermediate resolution regional targeting, and a narrow angle system for high resolution selective surveys. Camera electronics provide control of image clocking and on-board, internal editing and buffering to match whatever spacecraft data system capabilities are allocated to the experiment. The objectives of the MOC experiment follow.

Malin, M. C.↗
NASA NTRS1987

The properties of highly luminous IRAS galaxies

From a complete sample of 154 galaxies identified with IRAS sources in a 304 sq deg area centered on the South Galactic Pole, a subsample of 58 galaxies with L sub IR/L sub B > 3 was chosen. Low resolution spectra were obtained for 30% of the subsample and redshifts and relative emission line intensities were derived. As a class these galaxies are very luminous with < L sub IR > = 2.9 x 10 to the 11th power L sub 0 and (L sub IR) max = 1.3 x 10 to the 12th power L sub 0. CCD images and JHK photometry were obtained for many of the subsample. The galaxies are for the most part newly identified and are optically faint, with a majority showing evidence of a recent interaction. Radio continuum observations of all galaxies of the subsample were recently obtained at 20 cm VLA with about 75% being detected in a typical integration time of about 10 minutes.

Wolstencroft, R. D.↗
NASA NTRS1987

Ultraviolet Spectra of Two Magnetic White Dwarfs and Ultraviolet Spectra of Subluminous Objects Found in the Kiso Schmidt Survey

Low resolution International Ultraviolet Explorer (IUE) spectroscopic observations of two magnetic white dwarfs BPM25114 and K813-14 were obtained using both the SWP and LWP cameras. The first object has an observed magnetic field of 4 x 10(7) Gauss and the second has one of 3 x 10(7) Gauss. Both objects have overall spectral energy distributions appropriate for cool DA white dwarfs with T(eff) near 10,000 K and accordingly show strong lambda lambda 1400 and 1600 absorption in their spectra. Compared to non-magnetic DA white dwarfs of comparable effective temperature, there are some differences in the profiles, presumably produced by the magnetic fields in these objects. In addition, the ultraviolet spectra of a number of hot subluminous stars in the Kiso Schmidt survey were observed.

Wegner, Gary A.↗
NASA NTRS1987

Development of a stereo analysis algorithm for generating topographic maps using interactive techniques of the MPP

A local area matching algorithm was developed on the Massively Parallel Processor (MPP). It is an iterative technique that first matches coarse or low resolution areas and at each iteration performs matches of higher resolution. Results so far show that when good matches are possible in the two images, the MPP algorithm matches corresponding areas as well as a human observer. To aid in developing this algorithm, a control or shell program was developed for the MPP that allows interactive experimentation with various parameters and procedures to be used in the matching process. (This would not be possible without the high speed of the MPP). With the system, optimal techniques can be developed for different types of matching problems.

Strong, James P.↗
NASA NTRS1986

Kitt Peak spectroscopy of P/Halley: October 1983-March 1985

Four low-resolution optical spectra of P/Halley obtained at heliocentric distances between 8.78 ad 4.83 AU using the cryogenic camera and R-C spectrograph on the 4 m Mayall reflector of Kitt Peak National Observatory are discussed. The resulting spectrogram shows a lack of the emission bands commonly seen in nearby cometary spectra. The optical color of Halley indicates that the comet is redder than the sun at less than 6000 A and slightly bluer above 6500 A. The substantial extent of the Halley dust coma is discussed, and an oxygen production rate of 3 x 10 to the 26th atoms/s at r = 4.83 AU is derived. These results are compared with those for other comets and those found for Halley by other authors.

Spinrad, H.↗
NASA NTRS1986

The detection of global convective wave flows on the sun

Global convective flows in the solar convection zone have been predicted by theoretical interpretations of the global-scale ordering of magnetic fields and activity centers and by theoretical analyses of rotating convection zones. Direct evidence of these flows in the photosphere has not previously been found despite several long-term efforts. The signatures of such flows have now been detected by analyzing the daily series of low-resolution Dopplergrams obtained at the Wilcox Solar Observatory at Stanford University. The signatures are patterns of alternating east and west flows with amplitudes on the order of 25 m/s and longitudinal extent of about 30 degrees. The patterns move across the disc at approximately the solar rotation rate and have lifetimes of at least several rotations. Boundaries of the fast and slow flows are often associated with large magnetic active regions.

Scherrer, Philip H.↗
NASA NTRS1986

Ultraviolet variability and mass expulsion from R Aquarii

Ultraviolet spectra in the 1200-3200 A range indicate that the extended nebular features which resemble a jet in the peculiar variable R Aquarii (M7e + pec) increased in excitation in 1985. The emission properties of the compact H II region that surrounds the unresolved binary, and those of the extended nebular jet, have been analyzed from low-resolution IUE spectra of these regions. In particular, the UV line intensities observed in the jet appear variable on a time scale of about 1.5 yr. A new accretion disk model is proposed that explains the kinematic and ionization properties of discrete components which comprise the jet emission nebulosity, the appearance of the jet in the 1980s, and morphology that uniquely characterizes the R Aquarii system at radio, optical, UV, and X-ray wavelengths.

Kafatos, M.↗
NASA NTRS1986

Variability of ultraviolet emission in the carbon star TX Piscium

Multiple low-resolution IUE observations of the cool carbon star TX Psc (N0; C6, 2) permit an analysis of the variations in strength of the strongest emission lines - the Mg II line at 2800 A, the C II line at 2330 A, and certain Fe II lines. The integrated flux of the Mg II line varied by at least a factor of eight, while that of the C II line varies by at least a factor of five. The variations in Fe II may be considerably larger. The lines appear to vary together. The continuous flux in the best observed range from 2800 to 3200 A does not vary noticeably.

Johnson, Hollis R.↗
NASA NTRS1987

Coronagraph for astronomical imaging and spectrophotometry

A coronagraph designed to minimize scattered light in astronomical observations caused by the structure of the primary mirror, secondary mirror, and secondary support structure of a Cassegrainian telescope is described. Direct (1:1) and reducing (2.7:1) imaging of astronomical fields are possible. High-quality images are produced. The coronagraph can be used with either a two-dimensional charge-coupled device or photographic film camera. The addition of transmission dispersing optics converts the coronagraph into a low-resolution spectrograph. The instrument is modular and portable for transport to different observatories.

Vilas, Faith↗
NASA NTRS1987

Ultraviolet spectra and chromospheres of cool carbon stars

The authors assemble and discuss all available low-resolution IUE spectra of N-type carbon stars - including TW Hor, BL Ori, UU Aur, NP Pup, U Hya, T Ind, and TX Psc. Identification of spectral features is aided by a composite spectrum. Shortward of 2850 A only emission lines of C II, Mg II, Al II, and Fe II are seen, while the spectrum longward of 2850 A appears to be a photospheric absorption spectrum with a few superposed emission lines of Fe II. The most prominent absorption features are due to Fe I, CH, and CaCl. The emission feature at 2325 A, second only to Mg II in strength, is conclusively identified as C II (UV 0.01). Ultraviolet spectra of N-type carbon stars are similar to, though the emission-line fluxes are generally weaker than, those of the coolest M-giant stars available, such as HD 18191 (M6 III).

Johnson, Hollis R.↗
NASA NTRS1987

The dependence of ultraviolet chromospheric emission upon rotation among late-type stars

Integrated fluxes of chromospheric and transition region emission lines have been measured from low-resolution IUE spectra, obtained between 1981 and 1985, of a large number of chromospherically active stars. It is found that chromospherically active stars of the same R(C IV) show a spread in rotation rate that is as large as that of dwarf stars at fixed R(C IV) and that is correlated with spectral type. The UV emission of the active chromospheric stars decreases in strength with declining rotation rate, but shows little dependence upon rotation within individual luminosity classes. It is suggested that the lack of differences noted between rotation-activity relations for single, slowly rotating dwarf stars is due to the monotonic increase of both the average Rossby number and the average rotation period with later spectral type along the main sequence.

Simon, Theodore↗