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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 325 records · Page 18
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NASA NTRS2001

X-Ray Spectral Study of a Newly Ginga-Detected DQ Her

The goal of this proposal was to observe with ASCA, YY Dra, a DQ Her objected identified using archival Ginga data, in order to complete a high quality ASCA study of Ginga-detected DQ Her stars. There are relatively few DQ Her objects characterized by X-ray pulsations at the white dwarf spin period and optical pulsations at the orbital period and extremely complex X-ray spectra. The ASCA study included seven DQ Her objects. ASCA is able to resolve separate components of the Fe K emission and to set constraints on temperatures in the accretion column, and the mass of the white dwarf. The 40ksec observation, corresponding to roughly three orbital cycles, allowed the study of continuum changes with spin and orbital phase. The ASCA spectrum can be modelled as a bremsstrahlung with evidence for cold, helium-like and hydrogen-like iron emission, and helium-like argon emission. The lines yield a plasma temperature that is compatible with that from the continuum modelling (10-20 keV). The X-ray light-curve clearly shows sinusoidal variation from the spin pulse and shallow absorption dips at the orbital cycle. The derived parameters match well with the -accretion curtain, model for intermediate polars. The results will be presented together with the seven other DQ Her type sources observed with ASCA.

Vrtilek, S.↗
NASA NTRS1986

A spectroscopic study of the cataclysmic binary star SU Ursae Majoris

Spectroscopic observations of SU UMa, the prototype of a class of short-period cataclysmic binaries, are reported. The orbital period is found to be 0.076351 + or - 4.3 x 10 to the -5th days. The velocity amplitude of the emission line source is 58 + or - 4 km/s, leading to a mass function of about 0.0015 solar mass and implying a moderately low inclination. The line cores in H-alpha and H-beta lead the wings slightly in orbital phase, contrary to the predictions of simple hot spot models of the line core. The velocity widths of the Balmer series increase toward higher members of the series, suggesting that pressure broadening may contribute nonnegligibly to the emission line widths.

Thorstensen, John R.↗
NASA NTRS1982

The discovery of 50 minute periodic absorption events from 4U 1915-05

An analysis of X-ray observations shows that the steady flux from 4U 1915-05 undergoes periodic absorption dips with a period of 50 minutes. This period most probably represents the underlying orbital period of the system, and variations in the depth and duration of these events suggest that they are caused by a bulge on the edge of the accretion disk at the point where the gas stream impacts the disk. The mass-losing star in this system is probably a low-mass white dwarf, and the spectrum of the dips indicates that the metallicity of the absorbing material is at least a factor of 17 below solar values. The discovery of the 50-minute binary period supports earlier suggestions that X-ray burst sources are in binary systems.

White, N. E.↗
NASA NTRS1982

Amalthea

Voyager images have revealed Amalthea to be an irregular object 270 x 165 x 150 km in size. The spin period is probably synchronous with the orbital period of 11.9 hr, with the long axis pointing toward Jupiter. The satellite's surface is heavily scarred by impact craters, the largest of which has a diameter of 90 km (comparable to the mean radius of the satellite). Amalthea is very dark (reflectance about 5-6%) and very red, but isolated bright spots (reflectance up to 20%) occur. The spectrum of these bright spots is less red and may show an absorption feature near 0.6 micron. It is likely that the surface of Amalthea has been severely altered by its environment and by contamination from Io (especially by sulfur). It may, therefore, be very difficult to obtain definitive information on the composition of the intrinsic Amalthea material from remote sensing measurements.

Thomas, P.↗
NASA NTRS1985

Ultraviolet, optical, and infrared observations of the intermediate polar TV Columbae

Forty-three IUE spectra of the X-ray discovered, triply periodic cataclysmic variable, TV Col are examined. The results show that the UV flux varies with the four-day period discovered by Motch in 1981. By fitting continuum models to the UV and optical fluxes, it is inferred that this modulation corresponds to the periodic heating of a normally 9000 K source within the binary system due to reprocessing of beamed X-ray and (possibly) EUV radiation from the vicinity of the degenerate star. The observed flux from this heated source is consistent with its origin at either the disk hot spot or the secondary star. Phasing arguments, however, favor the identification of the latter as the primary reprocessing site in the system. The infrared observations are not consistent with the model proposed by Watts et al. in 1982 and imply that the four-day period does not correspond to the orbital period of the binary.

Mateo, M.↗
NASA NTRS1987

Optical and UV spectroscopy of the black hole binary candidate LMC X-1

Both further optical spectroscopy of the binary star identified with LMC X-1, obtained between 1983 and 1985, and a series of IUE UV spectra taken during a 5 day interval in 1984 are presented. The optical data are used to refine the orbital period to 4.2288 days, and improved orbital parameters are derived. The velocity of the optical emission lines is antiphased with the absorption lines and has twice the velocity amplitude. These new results support the estimates of the masses in the system given earlier. The most probable component masses are approximately 20 solar masses for the primary and near 6 solar masses (for the x-ray star), suggesting the the latter may be a black hole. The UV spectra show very weak, low-velocity stellar-wind lines. It is suggested that much of the surrounding medium is highly ionized by the X-ray flux. The 'nonwind' UV spectral lines and the UV continuum temperature are consistent with the optical data, indicating a late O type star of M(bol) = -8.5. There is a weak modulation of absorption-line strengths with orbital phase, suggestive of a lack of axisymmetry in the X-irradiation of the primary star and indicative of a fairly low orbital inclination.

Hutchings, J. B.↗
NASA NTRS1989

The photometric variability of the chromospherically active binary star HD 80715

Differential UBVRI photometry of the double-lined BY Dra system HD 80715 (K3 V + K3 V) obtained in December 1987 is presented. The star is found to be a variable with a full amplitude of 0.06 mag in V and a period similar or equal to the orbital period of 3.804 days. The mechanism of the variability is interpreted as rotational modulation due to dark starspots. In an attempt to detect chromospheric activity, high-resolution CCD spectra were obtained at Ca II H and K and at Fe I 6430 A and Ca I 6439 A, the photospheric lines normally used for Doppler imaging. HD 80715 shows double H and K emission features at a constant flux level for each component.

Strassmeier, Klaus G.↗
NASA NTRS1994

The Charon-Pluto mass ratio from MKO astrometry

Using the University of Hawaii (UH) 2.2-m telescope, we obtained charge coupled device (CCD) images of Pluto as it passed through a single field of 10 stars during 6 nights of Charon's 6.4-day orbital period. From these data, Charon's orbital semimajor axis is found to be 19,460 +/- 58 km, which is consistent with the recent measurement by Null et al. (1993), of 19,405 +/- 86 km. Our semimajor axis implies a system mass of (14.32 +/- 0.13) x 10(exp 24) g. From the motions of Pluto and Charon around their barycenter, we find that the ratio of Charon's mass to Pluto's is 0.1566 +/- 0.0035, indicating that the bodies both have densities near 2 g/cc. Our ratio is nearly twice that of Null et al., who find a ratio of 0.0837 +/- 0.0147. Possible reasons for the large discrepancy are discussed.

Young, L. A.↗
NASA NTRS1994

1ES 1113+432: Luminous, soft X-ray outburst from a nearby cataclysmic variable (AR Ursae Majoris)

A remarkable X-ray transient from the Einstein Slew Survey, 1 ES 1113+432, is identified with a nearby, short-period cataclysmic variable. Wenzel (1993) has confirmed that the optical counterpart is the variable star, AR UMa (cataloged as 'semiregular'), erroneously reported 5.7 min southeast of the true position. One of the Einstein slew observations recorded a flux of 43 IPC counts/s, which is an order of magnitude above the flux observed from the brightest cataclysmic variables in other X-ray surveys. The outburst spectrum is extremely 'soft,' with an implied blackbody temperature of approximately 22 eV. The optical counterpart (V = 16.5) exhibits a strong UV component, TiO bands from an M star, and broadened Balmer emission lines. Optical states as bright as V approx. 13 were found on photographs from the Harvard Plate Library, confirming outburst behavior in the optical counterpart. The historical photographic record suggests that 1ES 1113+432 remains in a low-accretion state most of the time. Both of the soft X-ray spectrum and the transitions between high and low-accretion states are suggestive of the AM Her (magnetic) subclass. Photometric observations in the I band show 0.18 mag modulations at a period of 0.966 hr. These are interpreted as ellipsiodal variations in the secondary star for a binary period of 1.932 hr, which is near the lower boundary of the 'period gap' in the histogram, of orbital periods of accreting white dwarfs. Thus 1ES 1113+432 provides the rare opportunity to study a secondary star in a cataclysmic binary that has evolved through the period gap. The optical spectral features from the secondary imply a spectral type of approximately M6 and a distance of approximately 88 pc. The peak luminosity in the soft X-ray component (unabsorbed) is then estimated to be 3 X 10(exp 33) ergs/s, assuming emission from a blackbody slab with a temperature of 22 eV. While this luminosity is higher than previous measures of the soft X-ray component, it does not exceed the amount of radiation that could be emitted from the accretion-heated surface of a white dwarf.

Remillard, R. A.↗
NASA NTRS1998

Identification of the Periodic Hard X-Ray Transient GRO J1849-03 with the X-Ray Pulsar GS 1843-02 = X1845-024: A New Be/X-Ray Binary

We identify the periodic transient hard X-ray source GRO J1849-03 with the transient x-ray pulsar GS 1843-02 = X1845-024 based on the detection of x-ray outbursts from X1845-024 coincident with hard x-ray outbursts of GRO J1849-03. Based on its spin period of 94.8 s and its orbital period of 241 days, we classify the system as a Be/X-ray binary.

Soffitta, P.↗
NASA NTRS1999

"X-Ray Transients in Star-Forming Regions" and "Hard X-Ray Emission from X-Ray Bursters"

This grant funded work on the analysis of data obtained with the Burst and Transient Experiment (BATSE) on the Compton Gamma-Ray Observatory. The goal of the work was to search for hard x-ray transients in star forming regions using the all-sky hard x-ray monitoring capability of BATSE. Our initial work lead to the discovery of a hard x-ray transient, GRO J1849-03. Follow-up observations of this source made with the Wide Field Camera on BeppoSAX showed that the source should be identified with the previously known x-ray pulsar GS 1843-02 which itself is identified with the x-ray source X1845-024 originally discovered with the SAS-3 satellite. Our identification of the source and measurement of the outburst recurrence time, lead to the identification of the source as a Be/X-ray binary with a spin period of 94.8 s and an orbital period of 241 days. The funding was used primarily for partial salary and travel support for John Tomsick, then a graduate student at Columbia University. John Tomsick, now Dr. Tomsick, received his Ph.D. from Columbia University in July 1999, based partially on results obtained under this investigation. He is now a postdoctoral research scientist at the University of California, San Diego.

Halpern, Jules P.↗
NASA NTRS2002

Thermal Analysis and Correlation of the Mars Odyssey Spacecraft's Solar Array During Aerobraking Operations

The Mars Odyssey spacecraft made use of multipass aerobraking to gradually reduce its orbit period from a highly elliptical insertion orbit to its final science orbit. Aerobraking operations provided an opportunity to apply advanced thermal analysis techniques to predict the temperature of the spacecraft's solar array for each drag pass. Odyssey telemetry data was used to correlate the thermal model. The thermal analysis was tightly coupled to the flight mechanics, aerodynamics, and atmospheric modeling efforts being performed during operations. Specifically, the thermal analysis predictions required a calculation of the spacecraft's velocity relative to the atmosphere, a prediction of the atmospheric density, and a prediction of the heat transfer coefficients due to aerodynamic heating. Temperature correlations were performed by comparing predicted temperatures of the thermocouples to the actual thermocouple readings from the spacecraft. Time histories of the spacecraft relative velocity, atmospheric density, and heat transfer coefficients, calculated using flight accelerometer and quaternion data, were used to calculate the aerodynamic heating. During aerobraking operations, the correlations were used to continually update the thermal model, thus increasing confidence in the predictions. This paper describes the thermal analysis that was performed and presents the correlations to the flight data.

Dec, John A.↗
NASA NTRS2003

A Thermal Analysis Approach for the Mars Odyssey Spacecraft's Solar Array

There are numerous challenges associated with placing a spacecraft in orbit around Mars. Often. trades must be made such as the mass of the payload and the amount of fuel that can be carried. One technique employed to more efficiently place a spacecraft in orbit while maximizing payload mass (minimizing fuel use) is aerobraking. The Mars Odyssey Spacecraft made use of aerobraking to gradually reduce its orbit period from a highly elliptical insertion orbit to its final science orbit. Aerobraking introduces its own unique challenges, in particular, predicting the thermal response of the spacecraft and its components during each aerobraking drag pass. This paper describes the methods used to perform aerobraking thermal analysis using finite element thermal models of the Mars Odyssey Spacecraft's solar array. To accurately model the complex behavior during aerobraking, the thermal analysis must be tightly coupled to the spatially varying, time dependent aerodynamic heating analysis. Also, to properly represent the temperatures prior to the start of the drag pass. the model must include the orbital solar and planetary heat fluxes. It is critical that the thermal behavior be predicted accurately to maintain the solar array below its structural flight allowable temperature limit. The goal of this paper is to describe a thermal modeling method that was developed for this purpose.

Dec, John A.↗
NASA NTRS2003

Aeroheating Thermal Model Correlation for Mars Global Surveyor (MGS) Solar Array

The Mars Global Surveyor (MGS) Spacecraft made use of aerobraking to gradually reduce its orbit period from a highly elliptical insertion orbit to its final science orbit. Aerobraking produces a high heat load on the solar arrays, which have a large surface area exposed to the airflow and relatively low mass. To accurately model the complex behavior during aerobraking, the thermal analysis needed to be tightly coupled to the spatially varying, time dependent aerodynamic heating. Also, the thermal model itself needed to accurately capture the behavior of the solar array and its response to changing heat load conditions. The correlation of the thermal model to flight data allowed a validation of the modeling process, as well as information on what processes dominate the thermal behavior. Correlation in this case primarily involved detailing the thermal sensor nodes, using as-built mass to modify material property estimates, refining solar cell assembly properties, and adding detail to radiation and heat flux boundary conditions. This paper describes the methods used to develop finite element thermal models of the MGS solar array and the correlation of the thermal model to flight data from the spacecraft drag passes. Correlation was made to data from four flight thermal sensors over three of the early drag passes. Good correlation of the model was achieved, with a maximum difference between the predicted model maximum and the observed flight maximum temperature of less than 5%. Lessons learned in the correlation of this model assisted in validating a similar model and method used for the Mars Odyssey solar array aeroheating analysis, which were used during onorbit operations.

Amundsen, Ruth M.↗
NASA NTRS1974

Periodic Trojan-type orbits in the earth-sun system

Periodic orbits about the triangular equilibrium points are found for the planar restricted three-body problem using the earth-sun system. The maximum semimajor axis for tadpole orbits ranges from the infinitesimal orbit at 1.000 AU to the near-limiting orbit at 1.00285 AU. Horseshoe orbits are found for 1.0029 to 1.0080 AU, larger horseshoes being unstable because of close approaches to the earth. Using stability tests devised by Rabe (1961, 1962), the limit of stability for nonperiodic orbits is found to occur for maximum semimajor axes near 1.0020 AU. In addition, near-periodic tadpole orbits appear to be stable against perturbations by Jupiter and Venus for periods of at least 10,000 yr. The possibility that minor planets actually exist in such orbits is considered.

Weissman, P. R.↗
NASA NTRS1995

Gaseous Vortices in Barred Spiral Galaxies

During the course of examining many two-dimensional, as well as a smaller sample of three-dimensional, models of gas flows in barred spiral galaxies, we have been impressed by the ubiquitous presence fo vortex pairs, oriented roughly perpendicular to their bars, with one vortex on each side. The vortices are obvious only when viewed in the bar frame, and the centers of their velocity fields usually are near Lagrangian points L(sub 4,5). In all models that we have studied, the vortices form on essentially the same time scale as that for the development of gaseous spiral arms, typically two bar rotations. Usually the corotation radius, r(sub c), lies slightly beyond the end of the bar. Depending upon the mass distributions of the various components, gas spirals either into, or out of, the vortices: In the former case, the vortices become regions of high density, whereas the opposite is true if the gas spirals out of a vortex. The models described in this paper have low-density vortices, as do most of the models we have studied. Moreover, usually the vortex centers lie approximately within +/- 15 deg of L(sub 4,5). In the stellar dynamic limit, when pressure and viscous forces are absent, short-period orbits exist, centered on L(sub 4,5). These orbits need not cross and therefore their morphology is that of gas streamlines, that is, vortices. We believe that the gas vortices in our models are hydrodynamic analogues of closed, short-period, libration orbits centered on L(sub 4,5).

England, Martin N.↗