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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 469 records · Page 26
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

The ultraviolet variability of early-type supergiants

Four early-type supergiants - HD 79186 (B5 Ia), HD 96919 (B9 Ia), HD 105056 (ON9.7 Iae), and HD 148379 (B2 Iae) - have been observed with the low-resolution spectrographs of IUE in the large aperture on 14 days. The behavior of the ultraviolet fluxes with time is studied. The light from all four stars seems to vary. Typically the dispersion about the mean magnitude at any wavelength corresponds to + or - 0.085, + or - 0.080, + or - 0.101, and + or - 0.106 mag, respectively. These amplitudes exceed the typical uncertainty in an IUE measurement of flux by about a factor of 3; they are somewhat larger than the variations known in the visible wavelength range. There are insufficient data to investigate periodicity in the observed light changes. The effective temperatures and angular diameters of the stars have been estimated using the present ultraviolet photometry, published UBV and uvby photometry, and the model-atmosphere fluxes reported by Kurucz in 1979. The program stars have dimensions typical for their spectral types. A brief discussion is given of possible causes of the variability of hot supergiants.

Underhill, A. B.↗
NASA NTRS1985

An analysis of scattered light in low dispersion IUE spectra

A detailed numerical simulation of light scattering from the low-resolution grating in the short wavelength spectrograph of the IUE Observatory was developed, in order to quantitatively analyze the effects of scattering on both continuum and line emission spectra. It is found that: (1) the redistribution of light by grating scattering did not appreciably alter either the shape or the absolute flux level of continuum spectra for A-F stars; (2) late-type stellar continua showed a tendency to flatten when observed in scattered light toward the shorter wavelengths; and (3) the effect of grating scattering on emission lines is to decrease measured line intensities by an increasing percentage toward the shorter wavelengths. The spectra obtained from scattering experiments for solar-type and late type stars are reproduced in graphic form.

Basri, G.↗
NASA NTRS1985

Chromospheric activity and TiO bands in M giants

Low-resolution IUE spectra of 23 cool giant stars ranging from K3 through M6 have been used to examine chromospheric activity in late-type giants. Previous studies have suggested a decrease in the fractional flux, normalized to bolometric flux, of the Mg II resonance lines (an indicator of chromospheric activity) with effective temperature. Using more accurately determined effective temperatures, this decrease is confirmed and found to be more rapid than previously suggested. A strong correlation is found between relative TiO band strengths, as measured by the Wing TiO index, and the level of chromospheric activity, as measured by Mg II fluxes. Cool giants which have weak TiO bands relative to the mean TiO strengths for stars of similar color also have Mg II lines that are weaker than the mean. Changes in composition and in chromospheric activity as a consequence of aging are suggested as a possible origin of this interesting relation.

Steiman-Cameron, T. Y.↗
NASA NTRS1985

Preliminary results on the various U.V. straylight sources for the VWFC onboard SL 1

Technical difficulties encountered using the Very Wide Field Camera (VWFC) during the Spacelab 1 Shuttle mission are reported. The VWFC is a wide low resolution (5 arcmin half-half width) photographic camera, capable of operating in both spectrometric and photometric modes. The bandpasses of the photometric mode of the VWFC are defined by three Al + MgF2 interference filters. A piggy-back spectrograph attached to the VWFC was used for observations in the spectrometric mode. A total of 48 astronomical frames were obtained using the VWFC, of which only 20 were considered to be of adequate quality for astronomical data processing. Preliminary analysis of the 28 poor-quality images revealed the following possible defects in the VWFC: darkness in the spacing frames, twilight/dawn UV straylight, and internal UV straylight. Improvements in the VWFC astronomical data processing scheme are expected to help identify and eliminate UV straylight sources in the future.

Viton, M.↗
NASA NTRS1985

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, P. H.↗
NASA NTRS1986

Digital filtering and acceleration pulse interpretation

It was concluded that the post processing digital filter is quite effective for removing unwanted high frequency and noise without distorting the signal. In addition, digital filtering is effective for smoothing low-level low resolution digital data where the digital stairstep phenomena are pronounced. Integrating the acceleration data to obtain velocity traces is quite useful. The velocity change provides a check on the validity of the acceleration trace. (Zero offsets in acceleration must be removed before integrating.) Average accelerations can be obtained from the velocity trace by dividing the change in velocity for an acceleration pulse by the pulse duration. One can obtain the peak of an equivalent triangular pulse by doubling the average acceleration.

Pasanella, E. L.↗
NASA NTRS1985

Radial growth of an extended spoke in Saturn's B ring

An analysis is reported of the pattern of radial growth of an extended spoke observed in the Voyager 2 low-resolution Saturn ring 'movie'. The feature is atypical in that it orbits Saturn at the corotational rate for 1-1/2 hours after the onset of its formation and then undergoes a 40-min acceleration to sustained Keplerian velocities. A correlation between the dynamical phases and the radial growth modes of the spoke is observed, one that seems consistent with the plasma cloud model of spoke formation and evolution proposed by Goertz and Morfill (1983), taken in the limit of high charge density.

Eplee, R. E., Jr.↗
NASA NTRS1985

Multispectral, thermal infrared satellite data for geologic applications

The value of multispectral thermal infrared satellite data for geologic mapping was assessed, applying the principal component and canonical analysis techniques to the images of the central part of the Arabian Peninsula (a 200 x 300 km area). Low resolution thermal infrared (TIR) data from the Nimbus 5 Surface Composition Mapping Radiometer (SCMR) and the NOAA-7 Advanced Very High Resolution Radiometer (AVHRR) were used. Color images included an 8.8 micrometer (SCMR) and 3.7 and 10.8 micrometer (AVHRR-night) data, ratioed AVHRR day/night TIR data, ratioed AVHRR reflected radiation data, and transformed 8- and 10-band TIR plus reflected radiation data. The results clearly demonstrated the potential geologic value of multispectral TIR data. Igneous and metamorphic units could be separated as a class (although not from each other except for young calc-alkaline granites). Some previously unmapped extensions of mapped faults below thick sedimentary units could be delineated. No single enhancement technique displayed all the potential information, implying that they should be used together.

Blodget, H. W.↗
NASA NTRS1985

A cryogenically cooled, multidetector spectrometer for infrared astronomy

A liquid helium-cooled, 24 detector grating spectrometer was developed and used for low resolution astronomical observations in the 5 to 14 micron spectral range. The instrument operated on the 91 cm Kuiper Airborne Observatory, the 3 m IRTF (Mauna Kea), the 3 m Shane telescope (Lick Observatory), and the 152 cm NASA and University of Arizona telescope. The detectors are discrete Si:Bi photoconductors with individual metal oxide semiconductor field effect transistor preamplifiers operating at 4 K. The system uses a liquid helium-cooled slit, order-sorter filter, collimator mirror, grating, and camera mirror arranged in a Czerny-Turner configuration with a cold stop added between the collimator mirror and the grating. The distances between components are chosen so that the collimator mirror images the secondary mirror of the telescope onto the cold stop, thus providing a very effective baffle. Scattered radiation is effectively reduced by using liquid helium-cooled, black baffles to divide the spectrometer into three separate compartments. The system noise-equivalent flux density, when used on the 152 cm telescope from 8 to 13 microns with a resolving power of 50, is 4.4 x 10 to the minus 17th power W/sq cm micron square root of Hz. The main applications are for measuring continuum radiation levels and solid state emission and absorption features in regions of star and planet formation.

Witteborn, F. C.↗
NASA NTRS1985

The intrinsic ultraviolet continua of O stars

Low-resolution IUE spectra of O and B stars in open clusters have been obtained. The main-sequence B stars are used to derive UV extinction curves for the program clusters, and these curves are used to determine the intrinsic UV to visual colors of O stars in NGC 2244, Trumpler 14, and NGC 6231. These data are analyzed in conjunction with the dereddened colors of O stars with color excesses less than 0.15 mag to obtain a set of reliable UV colors for O3-9, class V-I stars. The results can be summarized as follows: none of the observed O stars have UV colors significantly bluer than a normal B0 V star, and the late O supergiants have significantly redder UV colors than main-sequence O stars, although this luminosity distinction appears to vanish for the early O stars. Several possible explanations for these unexpected results are considered, but none of the presently available nonstandard models are sufficiently developed to be definitively tested.

Massa, D.↗
NASA NTRS1986

Spectral measurement of the Space Shuttle leeside shock layer and wake

Leeside shock layer and wake spectral radiation measured during the high altitude portion of the reentry of Space Shuttle Orbiter STS 51-D are presented and are compared with similar measurements obtained in an arc jet tunnel. The spectra, measured with a low-resolution spectral camera, are compared in order to identify the radiating species in a wavelength range from 4000 to 8000 angstroms. Emissions identified are: N2 first positive and N2 second positive systems, the N2(+) first negative system, and the sodium-D lines. No atomic air species or CN are observed. The spectra and procedure will be of use in comparison of flight flowfield properties with computational predictions and for guidance in developing future flight experiments.

Blackwell, H. E.↗
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.↗