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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 433 records · Page 24
All sourcesNASA NTRSDOE OSTI
NASA NTRS1999

In Pursuit of the FIP Effect in Late-Type Stellar Coronae

Spectral line data for several coronally active stars, in addition to EUVE Deep Survey light curves, have been analysed under this program. Much difficulty has been encountered in the study that has resulted in fewer stars being analysed than had been hoped. The difficulties stemmed from the analysis of low X-ray spectra taken with the ASCA satellite that produced results that are strongly discrepant with respect to the EUVE results. There is no obvious explanation for this, though it appears that analysis of ASCA data systematically underestimate metal abundance in hot plasmas. Consequently, the final emphasis in our analyses has been on EUVE data. Observed line profiles have being fitted in order to measure their fluxes using IDL software specially developed under this and parallel efforts.The observed line profiles deviate from pure gaussian forms, but we have found the benefits of using additional functional forms in the fitting process to be of only very small value for the lines with highest S/N. The resulting line fluxes have being processed in terms of the coronal EM using new techniques. Resulting EM distribution models are being used to finalize metallicity and abundance estimates for the stars in the program. Special account of the influence of missing lines in the spectral models has been taken.

Drake, Jeremy↗
NASA NTRS1999

The Most Distant X-Ray Clusters

In this program we have used ROSAT (Roentgen Satellite Mission) to observe X-ray emission around several high redshift radio galaxies in a search for extended, hot plasma which may indicate the presence of a rich galaxy cluster. When this program was begun, massive, X-ray emitting galaxy clusters were known to exist out to to z=0.8, but no more distant examples had been identified. However, we had identified several apparently rich clusters around 3CR radio galaxies at z greater than 0.8, and hoped to use ROSAT to confirm the nature of these structures as massive, virialized clusters. We have written up our results and submitted them as a paper to the Astrophysical Journal. This paper has been refereed and requires some significant revisions to accommodate the referees comments. We are in the process of doing this, adding some additional analysis as well. We will resubmit the paper early in 2000, and hopefully will meet with the referee's approval. We are including three copies of the submitted paper here, although it has not yet been accepted for publication.

Dickinson, Mark↗
NASA NTRS2000

Needs and Requirements for Future X-Ray Observations of Hot Galactic Halos

Galaxies are key objects for the study of cosmology, the life cycle of matter, and stellar evolution. X-ray observations have given us a new key window into these building blocks of the Universe, that allows us to investigate their hot gaseous component. While the study of these hot plasmas has important astrophysical and cosmological relevance, and significant, advances in our knowledge are expected from Chandra and XMM, there are a number of fundamental questions that require a next generation of X-ray telescopes. These telescopes need to be 10-30 square meter class telescopes, with Chandra-like resolution, and with a suite of instruments allowing spectral imaging at, moderate to high resolution.

Fabbiano, G.↗
NASA NTRS2000

The X-ray Spectral Evolution of eta Carinae as Seen by ASCA

Using data from the ASCA X-ray observatory, we examine the variations in the X-ray spectrum of the supermassive star nu Carinae with an unprecedented combination of spatial and spectral resolution. We include data taken during the recent X-ray eclipse in 1997-1998, after recovery from the eclipse, and during and after an X-ray flare. We show that the eclipse variation in the X-ray spectrum is apparently confined to a decrease in the emission measure of the source. We compare our results with a simple colliding wind binary model and find that the observed spectral variations are only consistent, with the binary model if there is significant high-temperature emission far from the star and/or a substantial change in the temperature distribution of the hot plasma. If contamination in the 2-10 keV band is important, the observed eclipse spectrum requires an absorbing column in excess of 10(exp 24)/sq cm for consistency with the binary model, which may indicate an increase in the first derivative of M from nu Carinae near the time of periastron passage. The flare spectra are consistent with the variability seen in nearly simultaneous RXTE observations and thus confirm that nu Carinae itself is the source of the flare emission. The variation in the spectrum during the flare seems confined to a change in the source emission measure. By comparing 2 observations obtained at the same phase in different X-ray cycles, we find that the current, X-ray brightness of the source is slightly higher than the brightness of the source during the last cycle perhaps indicative of a long-term increase in the first derivative of M, not associated with the X-ray cycle.

Corcoran, M. F.↗
NASA NTRS2002

Coronal Abundances In Xi Boo A, Abundances in the Corona of FK Aqr and the Origin of Cosmic Ray

Both Xi Boo A and FK Agr observations have been acquired, reduced and analysed. The results of the Xi Boo A study were published in ApJ (Drake, J.J., Kashyap, V., 2001, Up, 547, 428). Work is ongoing to determine the coronet metallicity of FK Aqr based on EUVE spectra and DO photometer data, using the techniques developed in the Drake & Kashyap paper. Preliminary synthetic spectra for FK Aqr have been developed, and further work to heap define the hot plasma emission measure distribution is underway. Progress on spectral analysis has been hampered following the post-doctoral scientist, Vinay Kashyap, taking up new position. A suitable replacement has been difficult to find, but new hire is expected shortly. However, good progress has been made on analysis of DO photometric variations in FK Age, with a publication now ready (Kashyap, V., Drake, J.J., Guedel, M., Audard, M.) for submission to a mainstream astrophysical journal.

Drake, Jeremy↗
NASA NTRS2002

Self-Consistent Magnetosphere-Ionosphere Coupling: Theoretical Studies

A self-consistent ring current (RC) model has been developed that couples electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self-consistent magnetosphere- ionosphere coupling loop. First, in addition to the RC ions, we solve an electron kinetic equation in our model. Second, using the relation of Galand and Richmond [2001], we calculate the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our code. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has has been comprehensively studied, and compare our results with different theoretical approaches. The self-consistent inclusion of the hot electrons and, their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self-consistent results) is evident in the inner magnetosphere. This changes the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells.

Khazanov, G. V.↗
NASA NTRS1989

Manufacturing Aids

During a research program, MMTC/Textron invented a computer-aided automatic robotic system for spraying hot plasma onto a turbine blade. The need to control the thickness of the plasma deposit led to the development of advanced optical gaging techniques to monitor and control plasma spray build-up on blade surfaces. The techniques led to computerized optical gages for inspecting aircraft, industrial turbine blades, etc. MMTC offers 10 standard commercial robotic gages. The system also generates two dimensional profiles for assessing status and specifying repairs to the electromechanical cathodes used to make the parts. It is capable of accuracies to a ten-thousandth of an inch. An expanded product line is currently marketed. The gages offer multiple improvements in quality control and significant savings.

Source record↗
NASA NTRS2002

Self-Consistent Magnetosphere-Ionosphere Coupling

A self-consistent ring current (RC) model has been developed that couples electron and ion magnetospheric dynamics with the calculation of the electric field. Two new features were taken into account in order to close the self-consistent magnetosphere-ionosphere coupling loop. First, in addition to the RC ions, we have solved an electron kinetic equation in our model. Second, using the relation of Galand and Richmond, we have calculated the height integrated ionospheric conductances as a function of the precipitated high energy magnetospheric electrons and ions that are produced by our model. To validate the results of our model we simulate the magnetic storm of May 2, 1986, a storm that has been comprehensively studied by Fok et al., and have compared our results with different theoretical approaches. The self-consistent inclusion of the hot electrons and their effect on the conductance results in deeper penetration of the magnetospheric electric field. In addition, a slight westward rotation of the potential pattern (compared to previous self-consistent results) is evident in the inner magnetosphere. These effects change the hot plasma distribution, especially by allowing increased access of plasma sheet ions and electrons to low L shells.

Six, N. Frank↗
NASA NTRS2002

Antimatter Driven P-B11 Fusion Propulsion System

One of the major advantages of using P-B11 fusion fuel is that the reaction produces only charged particles in the form of three alpha particles and no neutrons. A fusion concept that lends itself to this fuel cycle is the Magnetically Insulated Inertial Confinement Fusion (MICF) reactor whose distinct advantage lies in the very strong magnetic field that is created when an incident particle (or laser) beam strikes the inner wall of the target pellet. This field serves to thermally insulate the hot plasma from the metal wall thereby allowing thc plasma to burn for a long time and produce a large energy magnification. If used as a propulsion device, we propose using antiprotons to drive the system which we show to be capable of producing very large specific impulse and thrust. By way of validating the confinement propenies of MICF we will address a proposed experiment in which pellets coated with P-B11 fuel at the appropriate ratio will be zapped by a beam of antiprotons that enter the target through a hole. Calculations showing the density and temperature of the generated plasma along with the strength of the magnetic field and other properties of the system will be presented and discussed.

Kammash, Terry↗
NASA NTRS2004

The X-Ray Weakness of GPS Radio Galaxies: A Volume-Limited Complete Sample

The XMM observations of Mkn 668 have been analyzed. We found soft X-ray signatures of a hot plasma (kT approximately 10^7 approximately K) and a hard X-ray emission from the nucleus. The X-ray spectrum above 2.5 approximately keV is characterized by a very flat (observed photon index, Gamma approximately 0.5) power-law continuum, alongside with a strong Fe-K-alpha neutral iron fluorescent line (EW approximately 600 approximately eV). The best explanation for the origin of this high energy X-ray emission is in terms of the Compton-reflection of the nuclear emission. The primary X-ray emission is obscured by a Compton-thick (N_H approximately 10^24 approximately cm-2) matter which becomes transparent at higher energies. The observed above 2.5-keV X-rays are mostly due to reflection which is indicated by a strong Fe-K-alpha line. This represents the second hard X-ray detection of the GPS galaxy ever (the first one being 1345+125; O Dea et al. 2000). Interestingly, the both such trend is confirmed by our on going XMM-Newton observations of a larger GPS sample, it would lead us to looking into the question on how the dense nuclear environment impacts the nature and evolution of a GPS source, and more generally, on the history of radio power in the universe. The paper summarizing the results has been submitted to Astronomy and Astrophysics in December 2003.

Mushotzky, Richard F.↗
NASA NTRS2003

Self-Consistent Model of Magnetospheric Ring Current and Electromagnetic Ion Cyclotron Waves: The 2-7 May 1998 Storm

A complete description of a self-consistent model of magnetospheric ring current interacting with electromagnetic ion cyclotron waves is presented. The model is based on the system of two kinetic equations; one equation describes the ring current ion dynamics, and another equation describes the wave evolution. The effects on ring current ions interacting with electromagnetic ion cyclotron waves and back on waves are considered self-consistently by solving both equations on a global magnetospheric scale under nonsteady state conditions. The developed model is employed to simulate the entire 2-7 May 1998 storm period. First, the trapped number fluxes of the ring current protons are calculated and presented along with comparison with the data measured by the three- dimensional hot plasma instrument Polar/HYDRA. Incorporating in the model the wave-particle interaction leads to much better agreement between the experimental data and the model results. Second, examining of the wave (MLT, L shell) distributions produced by the model during the storm progress reveals an essential intensification of the wave emission about 2 days after the main phase of the storm. This result is well consistent with the earlier ground-based observations. Finally, the theoretical shapes and the occurrence rates of the wave power spectral densities are studied. It is found that about 2 days after the storm s main phase on 4 May, mainly non-Gaussian shapes of power spectral densities are produced.

Khazanov, G. V.↗
NASA NTRS2003

Thermal Iron K and Alpha: Line Emission from the X-Ray Binary GX 339-4

The accretion rate of the black hole candidate X-ray binary GX 339-4 in the 'off' state is low, and an advection dominated accretion flow (ADAF) is present. Hydrogen-like and helium-like iron Kbalpha; emission lines at 6.7 and 6.95 keV from hot plasma of ADAF can be produced by recombination-cascade processes with moderately high intensities, which are markedly distinguished from the fluorescent iron Kα line at approximately 6.4 keV. We show that the observational features of GX 339-4 can be explained by the ADAF model, if the iron abundance is more than 10 times the solar value, though the reason for such a high abundance is still unclear. We suggest that the increase of the accretion rate makes GX 339-4 change from off, low, intermediate, to high and very high states, and the line center of iron Kbalpha; will therefore shift from approximately 6.83 to approximately 6.4 keV, i.e. to the fluorescent disc-line, since the disappearance of the ADAF due to its high accretion rate.

Xu, Y. D.↗
NASA NTRS2004

An Evolving Trio of Hybrid Stars: C 111

Our goal is to understand the behavior of the outer atmosphere in this intermediate stage to create a comprehensive picture of atmospheric evolution. In the hybrid phase, the large-scale magnetic dynamo activity decays and hydrodynamic processes assume importance. Some hot plasma is still confined close to the star by magnetic loops, yet the confining field is breaking open, the atmosphere can escape through these open field lines, and the diffuse corona may be warm. There may well be a more extended and variable transition process. It remains for FUSE to identify the controlling parameters of the hybrid stars. It shows the positions of our 3 targets in the color-magnitude diagram where it is seen that they are at the extreme end of the hybrid region. Originally we had been awarded the hybrid star Iota Aur, but due to newly imposed pointing constraints of FUSE, that target was not accessible. And so we substituted Iota Dra, a giant of mass similar to our other targets but less evolved. In addition, Iota Dra was recently found to harbor a sub-stellar objects, possibly a planet, and so it could reveal the stellar environment of the planet. This substitution was accepted.

Oliversen, Ronald↗
NASA NTRS2004

Implementing Recommendations of the Columbia Accident Investigation Board

As many are aware, a piece of insulating foam liberated itself from the external tank and impacted the leading edge of Columbia during ascent on STS-107. It is believed that this impact left a hole in the thermal protection system (TPS), which protects the shuttle from hot plasma generated during re-entry. Unfortunately, the orbiter did not have the margin to withstand this compromise, and it is believed that the result of these events caused the loss of crew and orbiter.

Ottens, B.↗
NASA NTRS2005

Current Sheet Evolution in the Aftermath of a CME Event

We report on SOHO-UVCS observations of the coronal restructuring following a Coronal Mass Ejection (CME) on November 26,2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after a CME in the NW quadrant, UVCS began taking spectra at 1.7 solar radius, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the Fe XVIII emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by Ulysses-SWICS throughout the magnetic cloud associated with the CME. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Bemporad, A.↗
NASA NTRS2005

Coronal Current Sheet Evolution in the Aftermath of a CME

We report on SOHO-UVCS observations of coronal restructuring following a Coronal Mass Ejection (CME) on November 26, 2002, at the time of a SOHO-Ulysses quadrature campaign. Starting about 3 hours after the CME, which was directed towards Ulysses, UVCS began taking spectra at 1.7 solar radii, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 Angstrom line of [Fe XVIII], indicating temperatures above 6x10(6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature vs. time in the current sheet and estimate the density. Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by SWICS throughout the magnetic cloud associated with the CME, although the rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Bemporad, A.↗
NASA NTRS2006

Current Sheet Evolution In The Aftermath Of A CME Event

We report on SOHO UVCS observations of the coronal restructuring following a coronal mass ejection (CME) on 2002 November 26, at the time of a SOHO-Ulysses quadrature campaign. Starting about 1.5 hr after a CME in the northwest quadrant, UVCS began taking spectra at 1.7 R, covering emission from both cool and hot plasma. Observations continued, with occasional gaps, for more than 2 days. Emission in the 974.8 A line of [Fe XVIII], indicating temperatures above 6 x 10(exp 6) K, was observed throughout the campaign in a spatially limited location. Comparison with EIT images shows the [Fe XVIII] emission to overlie a growing post-flare loop system formed in the aftermath of the CME. The emission most likely originates in a current sheet overlying the arcade. Analysis of the [Fe XVIII] emission allows us to infer the evolution of physical parameters in the current sheet over the entire span of our observations: in particular, we give the temperature versus time in the current sheet and estimate its density. At the time of the quadrature, Ulysses was directly above the location of the CME and intercepted the ejecta. High ionization state Fe was detected by the Ulysses SWICS throughout the magnetic cloud associated with the CME, although its rapid temporal variation suggests bursty, rather than smooth, reconnection in the coronal current sheet. The SOHO-Ulysses data set provided us with the unique opportunity of analyzing a current sheet structure from its lowest coronal levels out to its in situ properties. Both the remote and in situ observations are compared with predictions of theoretical CME models.

Bemporad, A.↗
NASA NTRS2006

Lifetime Evolution of UV Jets

We report on observations acquired in May 2003 during a SOHO-Ulysses quadrature campaign. From May 25 to May 28, the SoHO LASCO Coronal Mass Ejection (CME) catalog lists a number of events which might have been observed by SOHO/UVCS, whose slit was centered along the Ulysses direction. However, because of time gaps in the observing schedule, or because of the unfavorable position of some CMEs, the most interesting events recorded by UVCS were a few short-lived ejections that represent the extension at higher altitudes of recursive EIT jets. We focus on jets occurring on May 26/27, visible also in EIT and LASCO images, which seem to propagate along the radial to Ulysses. UVCS spectra at 1.7 Rsun showed an unusually high emission in cool lines, lasting for about 10 to 25 minutes, with no evidence of hot plasma. Analysis of the cool line emission allowed us to infer the evolution of physical parameters during the jets lifetime and derive a crude estimate of the energy needed to account for their properties. We also looked for any evidence of the event in in situ data. Whether UVCS is observing jets or narrow CMEs is discussed in the contest of previous works on these classes of events and, in the last Section, we propose a scenario that accounts for our observations.

Corti, G.↗