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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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NASA NTRS1990

FG Sagittae - No hot companion?

The nucleus of the planetary nebula He 1-5 (= PK 60 -7 deg 1), the variable star FG Sge, was observed with the SWP camera of the International Ultraviolet Explorer satellite to detect a hot companion of the star, if such a companion exists. The observation found no evidence for the existance of a hot companion in the 1200-2000 A range of the SWP camera and supported the contention that FG Sge underwent a helium shell flash during the past century, and that the surrounding nebula, He 1-5, is a nebula of fossil ionization. Despite the currently accepted fossil ionization model, constraints posed by the satellite detection limit, the observed H-beta flux, and the adopted radii for white dwarfs still allow the possibility of a putative hot companion photoionizing this nebula.

Feibelman, Walter A.↗
NASA NTRS1993

Companions to bright S and MS stars - Technetium deficiency and binarity

To test the popular hypothesis that technetium-deficient stars of spectral types S and MS are mass-transfer binaries, we have searched for ultraviolet light from the putative hot secondaries in spectra taken with the SWP spectrograph of IUE. Although most S and MS stars are apparently thermally pulsing AGB (asymptotic giant branch) stars whose surfaces have been enriched with s-process elements and carbon dredged up from the interior, those stars whose spectra show enhanced s-process elements but no Tc are widely believed to be cooler analogs of the Ba II stars, which apparently owe their unusual abundances to prior mass transfer, the Tc from which has decayed away. We report IUE observations of 15 S and MS stars with the SWP, including the identification of six hot companions. Assembling all the IUE observations made to date, we find clear support for the mass-transfer hypothesis, confirming evidence from other lines of research. We further discuss the ages of the companions and the implications of these discoveries for stellar evolution.

Johnson, Hollis R.↗
NASA NTRS1992

UV variability and the nature of the continuum source in NGC5548

The short-wave UV continuum of NGC5548 varied quasi-periodically during the IUE monitoring from December 1988 to August 1989. The spectral index of this SWP continuum varied in tight correlation with it, inviting comparison with models to search for clues to the physical nature of the continuum source. The observed covariation of spectral index and continuum are consistent with the model of a black body of constant area (that of a sphere the size of Neptune's orbit) but variable temperature ( 18,000K to 25,000 K). A thin accretion disk around a black hole may also be consistent with this data if the accretion rate can be variable on time scales of 100 days while remaining uniform across the disk. There is marginal evidence for hysteresis in which spectral index changes lead changes in the SWP flux, although the CCF peaks at zero time lag.

Stoner, R. E.↗
NASA NTRS1993

IUE short-wavelength high-dispersion line list for the symbiotic nova RR Telescopii

An 820 minute and other long-exposure archival SWP IUE high-dispersion spectra of symbiotic star RR Tel have been combined to form a composite spectrum. In most of these spectra many lines are saturated, but weaker features appear above the continuum. Their wavelengths were measured from the composite spectrum and compared with the line list from a thorough study of RR Tel by Penston et al. (1983). Among the revised line list are 22 new line identifications from ions C III, O I, N I, Mg VI, Si I, S I, S IV, Fe II, and Ni II. N I exists inside RR Tel's H II region and is pumped by the hot component's continuum. The fluxes for all the lines in each of the spectra are presented. All of the observed ions show a secular flux decrease between 1978 and 1988. A list of SWP high-dispersion camera artifacts is also presented. The list was generated by comparing RR Tel spectra to a long-exposure sky flat.

Aufdenberg, Jason P.↗
NASA NTRS1993

UV spectral variability in the Herbig Ae star HR 5999. 11: The accretion interpretation

We report recent IUE high- and low-dispersion observations with the IUE long wavelength camera (LWP) and short wavelength camera (SWP) of the Herbig Ae star HR 5999. We have found a dramatic change in the structure of the Mg II h and k lines (2795.5, 2802.7 A) along with some continuum flux excesses especially at the short end of the SWP camera. LWP high dispersion observations of HR 5999 obtained between 1979 and 1990, at times of comparatively low UV continuum fluxes, exhibit P Cygni type m profiles in the Mg II resonance doublet. In contrast, observations made from September 1990 through March 16-18, 1992, with high W continuum fluxes, present Mg II lines with reverse P Cygni profiles indicative of some active episodic accretion. Accreting gas can also be detected in the additional red wings of the various Fe II and Mn II absorption lines, with velocities up to +300-350 km/s (September 1990). By September 10, 1992 the Mg II profile had returned to the type III P Cygni profile similar to those from earlier spectra. The correlation between the presence of large column densities of accreting gas and the continuum light variations supports suggestions by several authors that HR 5999 is surrounded by an optically thick, viscously heated accretion disk. Detection of accreting gas in the line of sight to HR 5999 permits us to place constraints on our viewing geometry for this system. A discussion is included comparing the spectral and physical similarities between HR 5999 and the more evolved proto-planetary candidate system, beta Pictoris.

Perez, M. R.↗
NASA NTRS2021

Automated Technique for the Detection of Step-Like Solar Wind Dynamic Pressure Changes: Application to the Response of the Transpolar Potential to Solar Wind Dynamic Pressure Fronts

The input from the solar wind (SW) and the accompanying Interplanetary Magnetic Field (IMF) is the defining feature of the solar wind-magnetosphere interactions. One of the most important SW drivers is the solar wind dynamic pressure, and most significantly its sharp changes known as pressure fronts. Sudden enhancements in solar wind dynamic pressure, SWP, have been shown to lead to intensification of the auroral electrojets (and Region 1 field-aligned currents), increase in auroral emissions, and significant enhancement in ionospheric convection and the transpolar potential. Case studies of the interaction between pressure fronts and the terrestrial space environment shed great light on their importance to the structure and dynamics of the system. However, thorough understanding of the interaction requires fully statistical investigations. These statistical studies require a large number of suitable pressure front events. In the past these have been obtained through laborious manual inspection of solar wind data. We present an automated procedure that identifies sudden step enhancements in SWP that satisfy a desired set of limiting step-like characteristics, such as magnitude of the change, sign of the change (positive/negative), and rate of change. The procedure yields a list of suitable events, along with their step features within minutes. The technique is tested for missed events and false positives by direct comparison to manual inspection of the data. Its utility is illustrated by application to the statistical effect of pressure fronts to the transpolar potential as measured by the Assimilative Mapping of Ionospheric Electrodynamics (AMIE) technique.

A. Boudouridis↗
NASA NTRS1980

Blackbody curves for the IUE spectral range lambda 1150 to lamda 3200 from 6,000 to 200,000 K

Two sets of blackbody curves are presented for the wavelength region covering the international ultraviolet explorer spectrographs. One set is normalized to unity at 3200 A, the other is normalized at 1900 A for those astronomers primarily interested in data for the SWP range. The blackbody curves extend from 1150 to 3200 A and cover the temperature range from 6,000 to 200,000K.

Feibelman, W. A.↗
NASA NTRS1981

Observations of polar aurora on Jupiter

North-south spatial maps of Jupiter were obtained with the SWP camera in IUE observations of 10 December 1978, 19 May 1979, and 7 June 1979. Bright auroral emissions were detected from the north and south polar regions at H Ly alpha (1216 A) and in the H2 Lyman bands (1250-1608 A) on 19 May 1979; yet no enhanced polar emission was detected on the other days. The relationship between the IUE observing geometry and the geometry of the Jovian magnetosphere is discussed.

Lane, A. L.↗
NASA NTRS1981

IUE spectra of F and late A stars

The International Ultraviolet Explorer (IUE) spectra of alpha CMi (F5 IV-V), beta Cas (F2 IV), alpha Car (F0 Ib), and gamma Boo (A7 III) in the context of the question as to whether chromospheres disappear in the early F late A portions of the Hertzsprung-Russell diagram. Both alpha CMi (Procyon) and beta Cas show bright emission line spectra indicative of chromospheres and transition regions, but neither alpha Car (Canopus) nor gamma Boo show any evidence of emission in their SWP spectra or at the Mg II lines, despite very deep exposures. Alpha CMi has emission line fluxes roughly 6 times those of the quiet Sun, but the rapidly rotating delta Scuti type variable beta Cas has surface fluxes 10 to 50 times those of the quiet Sun. Upper limits on emission line fluxes for alpha Car are 4 to 20 and for gamma Boo 15 to 80 times the quiet Sun. It is concluded that the apparent absence of emission lines in the spectra of alpha Car and gamma Boo should not be interpreted as due to the absence of nonradiatively heated outer atmospheres in stars hotter than spectral type F0, but rather to the inability to see emission lines with IUE against a background of scattered light and a bright photospheric absorption line spectrum either in low or high dispersion.

Linsky, J. L.↗
NASA NTRS1981

Results of basic improvements to the extraction of spectra from IUE images

Results of two methods of extracting spectra from IUE images are compared. The first method, which is presently implemented, performs a geometric correction of the image followed by a photometric correction. The spectral data are then extracted using a slit with an effective width and sampling interval of 2.4A for the SWP camera and 3.7A for the LWR camera in low dispersion. The second method performs the photometric correction without doing a geometric correction. The spectral data are then extracted from the photometrically corrected image by an extraction slit, which follows the spectral orders in the nongeometrically corrected space, with an effective width and sampling interval 1/2 that of the present method.

Lindler, D. J.↗
NASA NTRS1981

Improvements to the accuracy of the IUE wavelength scales in high dispersion

The data base of Pt-Ne emission lines used to calibrate the IUE high dispersion wavelength scales was scrutinized to improve the internal consistency of the adopted laboratory wavelength values and provide a homogeneous, documented line list, which IUE Guest Observers may use to evaluate quantitatively those Pt-Ne spectra taken to calibrate their data. After deletion of incorrect or inappropriate data in the old data base (lines with incorrect wavelength assignments; lines which are too faint, too bright, or blended; lines which fall near reseau marks, etc.) and the addition of several new entries, a total of 172 Pt-Ne lines for the SWP camera and 164 Pt-Ne lines for the LWR camera are now used for routine wavelength calibration in the high dispersion mode.

Turnrose, B. E.↗
NASA NTRS1981

Effects of temperature fluctuations of IUE data quality

Analysis of IUE calibration lamp images shows that variation in the temperature of the scientific instrument causes shifts in the location of the spectral format with respect to the reseau grid on the detector and in the location of the reseaux themselves. In high dispersion, a camera head amplifier temperature difference of 6C corresponds to a shift of 4 pixels in the spectral format for LWR and 2 pixels for SWP along the dispersion direction. Shifts perpendicular to the disperson (for the same temperature difference) are less than one pixel for both cameras. In low dispersion spectra, the shifts are similar but orthogonal to those described above with the larger motion lying in the direction perpendicular to the dispersion. In both dispersion modes, the observed shifts are apparently independent of wavelength. In high dispersion, the constant pixel shift mimics a constant velocity error.

Thompson, R. W.↗
NASA NTRS1981

Quasi-simultaneous observations of BL Lac object Mrk 501 in X-ray, UV, visible, IR, and radio frequencies

Observations in the X-ray, UV, visible, IR and radio regions of the BL Lac object Mrk 501 made over the course of two months are reported. The measurements were made with the A2 experiment on HEAO 1 (X-ray), the SWP and LWR cameras on IUE (UV), the 5-m Hale telescope (visible), the 2.5-m telescope at Mount Wilson (IR), the NRAO 92-m radio telescope at Green Bank (4750 MHz) and the 46-m radio telescope at the Algonquin Observatory (10275 and 10650 MHz). The quasi-simultaneously observed spectral slope is found to be positive and continuous from the X-ray to the UV, but to gradually flatten and possibly turn down from the mid-UV to the visible; the optical-radio emission cannot be accounted for by a single power law. The total spectrum is shown to be compatible with a synchrotron self-Compton emission mechanism, while the spectrum from the visible to the X-ray is consistent with synchrotron radiation or inverse-Compton scattering by a hot thermal electron cloud. The continuity of the spectrum from the UV to the X-ray is noted to imply a total luminosity greater than previous estimates by a factor of 3-4.

Kondo, Y.↗
NASA NTRS1981

Simultaneous X-ray, ultraviolet, optical, and radio observations of the flare star Proxima Centauri

Results of coordinated program of observations in the X-ray, UV, optical and radio regions of the dM5e flare star Proxima Centauri are presented. Simultaneous observations of the star were obtained on March 6 and March 7, 1979, by the Einstein Observatory IPC, the IUE SWP and LWR cameras at low dispersion, three ground-based optical telescopes in Australia and the Parkes 64-m radio telescope. A total of 10 radio bursts and six optical flares was detected during three nights of simultaneous radio and optical observations, which appear to be broadly correlated. A major X-ray flare event was detected with temperatures of 1.7 x 10 to the 7th and 1.2 x 10 to the 7th K during the rise and decay phases, respectively, respective X-ray fluxes of 3.0 x 10 to the -11th and 3.7 x 10 to the -11th ergs/sq cm per sec, and changes in spectral flux distribution. No radio, optical or UV flare emission corresponding to the X-ray flare was detected. The X-ray flare is interpreted in terms of an arch model with cooling predominantly by X-ray radiation, with an electron density of 1.0 x 10 to the 11th/cu cm during the decay phase and a total arch length comparable to the size of the star itself. The X-ray flare observed is thus more similar to a typical strong solar flare than heretofore seen on a flare star.

Haisch, B. M.↗
NASA NTRS1982

The IUE echelle blaze function

An improved form for the echelle blaze function derived by Ake (1981) was used to study the apparent variation of grating constant K with order m for the long and short wavelength spectrographs. For the LWR camera, early images indicate that K should vary linearly with order. It is suggested that this represents a rotation of the observed blaze centers on the camera compared to a constant K=m lambda line. In four years of use, changes in sensitivity across the camera changed the observed blaze function, inducing a curvature in the K versus m relation. This curvature varies in time with variations in camera response. The SWP camera shows these effects to a lesser degree.

Ake, T. B.↗
NASA NTRS1982

High dispersion observations of selected regions in the Orion Nebula

High resolution spectral observations were made of several regions of the Orion Nebula near theta (2) Ori A using the IUE. The positions were selected using a moderate spatial resolution map from a previous low dispersion IUE survery of this section of the nebula. With the SWP and LWR cameras, 28 pectra were obtained of the bright bar, three Taylor-Munch cloudlets, and several surrounding locations. Emission lines of He, C, N, O, Mg, and Si allow a characterization of these cloudlets and of the gas in and around the bar. Small aperture observations provide radial velocity information for the ultraviolet emission of these features. These data show ionization variations from region to region and are suggestive of stellar wind interactions between the cloudlets and theta(2) Ori A.

Boeshaar, G. O.↗
NASA NTRS1982

IUE observations of reflection nebulae

Low-resolution IUE spectra in the SWP and LWR ranges were obtained of several reflection nebulae in the vicinity of their respective illuminating stars. Data for NGC 7023 (HD200775), NGC 1435 (Merope, 23 Tau), NGC 1432 (Maia, 20 Tau) and the Electra (17 Tau) nebula were found to display significant differences in the shape of their normalized nebular spectra. If the dust in these nebulae is similar from one object to the next, these differences can be most readily explained by differences in the line-of-sight dust distribution, coupled with a wavelength-dependent phase function, changing from a strongly forward throwing form (g = 0.6-0.7) in the visible to a more nearly isotropic shape (g approximately 0.25) at 1400A.

Witt, A. N.↗
NASA NTRS1982

Analysis of non-interacting binaries with luminous cool primaries

High dispersion long wave redundant (LWR) spectra are analyzed for the differential velocity between hot and cool components of heretofore single lined spectroscopic binaries with late type giant or supergiant primaries. Cross correlation of a composite spectrum against early and late type standard stars yields relative velocities with an accuracy of 0.2 to 0.3 kms. When the orbit of the primay is known, the differential measurement from IUE gives the mass ratio of the system. Low dispersion short wave prime (SWP) and LWR flux spectra are used together with ground-based photometry to disentangle the composite energy distributions of the binaries. Temperatures of both components, their relative luminosities, and the reddening of the system are obtained. Assuming the hot secondaries to be main sequence stars, their probable luminosities and masses may be obtained from their temperatures. Then absolute magnitudes and masses may be obtained for the evolved primaries with more confidence than with existing techniques.

Parsons, S. B.↗