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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 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
NASA NTRS1983

Interpretation of 2-probe turbulence measurements in an axisymmetric contraction

Simultaneous measurements of the streamwise and radial velocity components at two points, one on and one off the centerline with variable radial separation, were digitally recorded and processed at several stations along a four to one contraction with controlled upstream turbulence conditions. Various statistical quantities are presented including spectra and coherence functions. The integral L sub ux, L sub um, L sub vx, L sub vm were also estimated and their variation along the contraction is examined.

Marion-Moulin, C.↗
NASA NTRS1983

Infrared observations of RS CVn stars

The paper presents infrared photometry of the RS CVn binary stars AR Lac (1.2-10 microns) and MM Her (1.2-3.5 microns) as they egressed from their primary and secondary eclipses; of the eclipsing systems RS CVn and Z Her at maximum light (1.2-10 microns) and of the non-eclipsing systems UX Ari and HR 1099 (1.2-10 microns). An analysis of these and published V data based on flux ratio diagrams (linear analogues of color-color diagrams) shows that G and K stars supply the infrared light of these systems. In AR Lac, the combined light of a G5-K0 subgiant and either a late F dwarf or an early F subgiant can account for the observed visual and infrared light curves. None of these systems shows infrared emission from circumstellar matter. This result is simply understood: dust grains would not be expected to form in the physical conditions surrounding the subgiant, and the corona and chromosphere (whose properties have been deduced from spectroscopic X-ray observations) should not produce appreciable infrared emission.

Berriman, G.↗
NASA NTRS1984

PG 1012-029 - A high-excitation eclipsing cataclysmic variable

The paper presents a photometric and spectrophotometric analysis of a new eclipsing cataclysmic variable, PG 1012-029, with an orbital period of 3 hr 14 minutes 18.7 s. The eclipse depth reaches 1.9 mag, is rounded at minimum, and shows a prolonged egress 'shoulder', as found for UX UMa and some other eclipsing systems. The spectrum shows strong high-excitation lines at optical and UV wavelengths. A large fraction of the He II flux disappears during the eclipse, when the hydrogen spectrum fits a cooler temperature, and the continuum reddens. This behavior is attributed to eclipse of the hotter inner disk region.

Penning, W. R.↗
NASA NTRS1984

CPD -48 deg 1577 - The brightest known cataclysmic variable

The discovery is reported of a V = 9.4 mag star which has the properties of a cataclysmic variable. Its UBV colors are similar to those of UX UMa, and its brightness fickers with an amplitude of the order of 0.1 mag. Larger brightness variations (0.5 mag) are found on a time scale of years. Its spectrum is characterized by extremely weak absorption lines of He I and He II, as well as extremely broad, shallow lines of H. A broad K line is very weakly present in absorption. Emission cores with a very slow decrement are seen in the H lines. From a comparison with the known properties of other cataclysmic variables, the distance, reddening, and mass exchange rate are estimated. The space density of cataclysmic variables is also estimated, since the original spectroscopic survey is complete to magnitude B = 10.0.

Krzeminski, W.↗
NASA NTRS1985

A summary of the UV, optical and IR properties of disks in CV's

The available observations of dwarf novae and novalike systems that are relevant to the study of accretion in cataclysmic variables are reviewed. This includes UV data from IUE and optical spectroscopy and infrared photometry. The flux distributions are compared to available steady state models to obtain an estimate of the mass accretion and the range of this parameter among the dwarf novae (U Gem, Z Cam and SU UMa types) and the novalikes (UX UMa, AM Her, DQ Her types). The normal and abnormal range of variation in the continuum and line fluxes is discussed.

Szkody, P.↗
NASA NTRS1985

Radio polarization characteristics of two RS CVn binaries

The results of multifrequency epoch VLA observations of polarized radio emission from the nearby active RS CVn binaries UX Arietis and HR 1099 are reported. For both systems, there is an excellent correlation between handedness of circular polarization and frequency. Helicity reversal is almost always seen between 1.4 and 5.0 GHz, possibly due to optical depth effects. There may also be an anticorrelation between total intensity and fractional circular polarization, especially at 5 GHz. This is consistent with models in which intense flares are associated with compact selfabsorbed synchrotron sources, while the quiescent emission arises from larger gyrosynchrotron-emitting plasma.

Mutel, R. L.↗
NASA NTRS1986

Orbital flight simulation utility software unit specifications

The HP PASCAL source code contained in pages 6 through 104 was developed for the Mission Planning and Analysis Division (MPAD) and takes the place of detailed flow charts defining the specifications for a Utility Software Unit designed to support orbital flight simulators such as MANHANDLE and GREAS (General Research and Engineering Analysis Simulator). Besides providing basic input/output, mathematical, vector, matrix, quaternion, and statistical routines for such simulators, one of the primary functions of the Utility Software Unit is to isolate all system-dependent code in one well-defined compartment, thereby facilitating transportation of the simulations from one computer to another. Directives to the PASCAL compilers of the HP-9000 Series 200 PASCAL 3.0 operating system and the HP-9000 Series 500 HP-UX 5.0 operations systems are also provided.

Wilson, S. W.↗
NASA NTRS1986

Where do flares occur in RS CVn systems? Analysis of the October 3, 1981 flare on V711 Tau = HR 1099 observed by IUE

A set of IUE observations of V711 Tau = HR 1099 (K1 IV and G2 V) in which high-resolution spectra with the SWP and LWR cameras were obtained during the luminous flare of October 3, 1981 is discussed. Multigaussian fits to the Mg II k and C IV 1548 A lines are consistent with the flare radial velocity being identical to that of the K star. Thus, the flare probably occurred on the K star. There is no evidence for flows as seen during a flare on UX Ari. The strongest emitters of UV radiation during the flare were the L alpha and Mg II lines, which emitted seven times as much energy as all the transition region lines combined. The peak luminosity of the flare in the UV emission lines is 1.5 times 10 to the 31st power ergs/sec, and the total emission in these lines during the flare was about 4 times 10 to the 35th power ergs.

Linsky, J. L.↗
NASA NTRS1986

Radio wavelength observations of magnetic fields on active dwarf M, RS CVn and magnetic stars

The dwarf M stars, YZ Canis Minoris and AD Leonis, exhibit narrow-band, slowly varying (hours) microwave emission that cannot be explained by conventional thermal radiation mechanisms. The dwarf M stars, AD Leonis and Wolf 424, emit rapid spikes whose high brightness temperatures similarly require a nonthermal radiation process. They are attributed to coherent mechanisms such as an electron-cyclotron maser or coherent plasma radiation. If the electron-cyclotron maser emits at the second or third harmonic gyrofrequency, the coronal magnetic field strength equals 250 G or 167 G, and constraints on the plasma frequency imply an electron density of 6 x 10 to the 9th/cu cm. Radio spikes from AD Leonis and Wolf 424 have rise times less than or equal to 5 ms, indicating a linear size of less than or equal to 1.5 x 10 to the 8th cm, or less than 0.005 of the stellar radius. Although Ap magnetic stars have strong dipole magnetic fields, they exhibit no detectable gyroresonant radiation, suggesting that these stars do not have hot, dense coronae. The binary RS CVn star UX Arietis exhibits variable emission at 6 cm wavelength on time scales ranging from 30 s to more than one hour.

Lang, Kenneth R.↗
NASA NTRS1989

500-3200 A observations of the interacting binary stars V356 Sgr and Beta Lyr

Results on VG356 Sgr and Beta Lyr are presented from the Voyager UV spectrometers and the IUE. The observations of V356 Sgr cover two eclipses in which the total strength of the UV emission lines were invariant. At wavelengths shorter than 1600 A, an uneclipsed UV continuum was found. A model for the origin of the circumstellar matter in V356 Sgr is given. The UV observations of Beta Lyr show a strong far-UV continuum down to 912 A. The spectral shape fo the far-UV continuum closely resembles that of a UX Uma-type cataclysmic variable. Analysis of the Beta Lyr data indicates that the central object is small, with a radius on the order of 1 solar radius or less.

Polidan, R. S.↗
NASA NTRS1992

Ginga observations of X-ray flares on Algol

The Ginga X-ray satellite observed Algol (Beta Per) for 2 days in 1989 January, including both the primary optical eclipse and most of the secondary eclipse. We derive upper limits of about 20 and 10 percent, respectively, for the eclipsed flux fraction during the two eclipses. A large flare lasting over 12 hr was seen prior to and during secondary eclipse. High-temperature Fe line emission is clearly detected in the proportional counter data. The Fe line equivalent width is variable during the flare, ranging from 0.4-1.0 keV. Except for two intervals during the flare rise, the observed equivalent width is lower than predicted using solar abundances and an optically thin plasma model. Similar behavior has also been observed by Ginga in a large flare on UX Ari: in both events, opacity effects at line center may be playing a significant role. Loop model analysis of the large flare suggests that it involves a substantially longer loop or loops than a shorter duration Algol flare seen with Exosat.

Stern, R. A.↗
NASA NTRS1993

Transient dynamics capability at Sandia National Laboratories

A brief overview of the transient dynamics capabilities at Sandia National Laboratories, with an emphasis on recent new developments and current research is presented. In addition, the Sandia National Laboratories (SNL) Engineering Analysis Code Access System (SEACAS), which is a collection of structural and thermal codes and utilities used by analysts at SNL, is described. The SEACAS system includes pre- and post-processing codes, analysis codes, database translation codes, support libraries, Unix shell scripts for execution, and an installation system. SEACAS is used at SNL on a daily basis as a production, research, and development system for the engineering analysts and code developers. Over the past year, approximately 190 days of CPU time were used by SEACAS codes on jobs running from a few seconds up to two and one-half days of CPU time. SEACAS is running on several different systems at SNL including Cray Unicos, Hewlett Packard PH-UX, Digital Equipment Ultrix, and Sun SunOS. An overview of SEACAS, including a short description of the codes in the system, are presented. Abstracts and references for the codes are listed at the end of the report.

Attaway, Steven W.↗
NASA NTRS1994

Observational studies of the clearing phase in proto-planetary disk systems

A summary of the work completed during the first year of a 5 year program to observationally study the clearing phase of proto-planetary disks is presented. Analysis of archival and current IUE data, together with supporting optical observations has resulted in the identification of 6 new proto-planetary disk systems associated with Herbig Ae/Be stars, the evolutionary precursors of the beta Pictoris system. These systems exhibit large amplitude light and optical color variations which enable us to identify additional systems which are viewed through their circumstellar disks including a number of classical T Tauri stars. On-going IUE observations of Herbig Ae/Be and T Tauri stars with this orientation have enabled us to detect bipolar emission plausibly associated with disk winds. Preliminary circumstellar extinction studies were completed for one star, UX Ori. Intercomparison of the available sample of edge-on systems, with stars ranging from 1-6 solar masses, suggests that the signatures of accreting gas, disk winds, and bipolar flows and the prominence of a dust-scattered light contribution to the integrated light of the system decreases with decreasing IR excess.

Grady, Carol A.↗
NASA NTRS1994

IUE observations of new A star candidate proto-planetary systems

As a result of the detection of accreting gas in the A5e PMS Herbig Ae star, HR 5999, most of the observations for this IUE program were devoted to Herbig Ae stars rather than to main sequence A stars. Mid-UV emission at optical minimum light was detected for UX Ori (A1e), BF Ori (A5e), and CQ Tau (F2e). The presence of accreting gas in HD 45677 and HD 50138 prompted reclassification of these stars as Herbig Be stars rather than as protoplanetary nebulae. Detailed results are discussed.

Grady, Carol A.↗
NASA NTRS1994

Catalogue of UBVRI photometry of T Tauri stars and analysis of the causes of their variability

A computer-based catalogue of UBVRI photoelectric photometry of T Tauri stars and their earlier type analogs has been compiled. It presently includes over 10 000 entries on 80 stars and will be updated on a regular basis; it is available on Internet. The catalogue is used to analyze the sometimes bizarre light variations of pre-main-sequence stars on time scales of days to months in an attempt to illuminate the nature and causes of the phenomenon. It is useful in discussing their light variations to divide the stars into three groups according to their spectra. These are: weak T Tauri stars (WTTS; spectral class later than K0 and W(sub H-alpha less than 10 A), classical T Tauri stars (CTTS; spectral class later than K0 and W(sub H-alpha) greater than 10 A), and early type T Tauri stars (ETTS; spectral class of K0 or earlier). Three distinct types of variability are displayed by stars in the catalogue. Type I variations are periodic in VRI and undoubtedly caused by rotational modulation of a star with an asymmetric distribution of cool spots on its surface. Irregular flare activity is sometimes seen on such stars in U and B. Type I variations are easiest to see on WTTS but are clearly present on CTTS and ETTS as well. Type II variations are caused by hot 'spots' or zones and, it is argued, result from changes in the excess or 'veiling' continuum commonly attributed to an accretion boundary layer or impact zone of a magnetically channeled accretion flow. This type of variation is seen predominantly or solely in CTTS. A subcategory, designated Type IIp, consists of stars which display periodic variations caused by hot spots. Whereas cool spots may last for hundreds or thousands of rotations, hot spots appear to come and go on a much shorter time scale. This suggests that both unsteady accretion and rotation of the star contribute to Type II variations. It is shown that a third type of variation exists among ETTS, including stars as early as A type. UX Ori is a typical example and we call these Type III variables or UXors. Their distinguishing characteristic is that they can display very large amplitudes (exceeding 2.8 mag in V) while showing little or no evidence for a veiling continuum or any substantial change in their photospheric spectra. If Type III variations are caused by changes in accretion luminosity, then boundary layers or impact zones in ETTS must be much different from CTTS which, of course, is possible since mass accretion rates are probably much higher. However, the leading hypothesis for explaining Type III variations is variable obscuration by circumstellar dust. It is argued that the putative dust clumps causing such variations cannot be confined to a disk; otherwise UXors would be rare. Perhaps magnetic effects are involved in levitating accreting dust out of the plane, as has been suggested for CTTS, or perhaps we are witnessing continuing infall of clumps from placental clouds. A third possibility is that dust may be condensing in an outflow.

Herbst, William↗
NASA NTRS1995

Ultraviolet eclipse observations of an accretion disk wind

We present eclipse time series of ultraviolet CIV 1549A and HeII profiles in the spectrum of the nova-like variable UX UMa, obtained using the Goddard High Resolution Spectrometer (GHRS) on board the Hubble Space Telescope (HST). These data provide important new insights into the origin of these mainly wind-formed lines. Specifically, they show that the shallow line eclipses first discovered in International Ultraviolet Explorer (IUE) observations are due to the occultation of superposed narrow absorption features and provide the first clear evidence that the outflows in high-state cataclysmic variables (CV) are rooted in the inner accretion disk.

Drew, J. E.↗
NASA NTRS1996

UNIX-based operating systems robustness evaluation

Robust operating systems are required for reliable computing. Techniques for robustness evaluation of operating systems not only enhance the understanding of the reliability of computer systems, but also provide valuable feed- back to system designers. This thesis presents results from robustness evaluation experiments on five UNIX-based operating systems, which include Digital Equipment's OSF/l, Hewlett Packard's HP-UX, Sun Microsystems' Solaris and SunOS, and Silicon Graphics' IRIX. Three sets of experiments were performed. The methodology for evaluation tested (1) the exception handling mechanism, (2) system resource management, and (3) system capacity under high workload stress. An exception generator was used to evaluate the exception handling mechanism of the operating systems. Results included exit status of the exception generator and the system state. Resource management techniques used by individual operating systems were tested using programs designed to usurp system resources such as physical memory and process slots. Finally, the workload stress testing evaluated the effect of the workload on system performance by running a synthetic workload and recording the response time of local and remote user requests. Moderate to severe performance degradations were observed on the systems under stress.

Chang, Yu-Ming↗
NASA NTRS1996

ARTSN: An Automated Real-Time Spacecraft Navigation System

As part of the Deep Space Network (DSN) advanced technology program an effort is underway to design a filter to automate the deep space navigation process.The automated real-time spacecraft navigation (ARTSN) filter task is based on a prototype consisting of a FORTRAN77 package operating on an HP-9000/700 workstation running HP-UX 9.05. This will be converted to C, and maintained as the operational version. The processing tasks required are: (1) read a measurement, (2) integrate the spacecraft state to the current measurement time, (3) compute the observable based on the integrated state, and (4) incorporate the measurement information into the state using an extended Kalman filter. This filter processes radiometric data collected by the DSN. The dynamic (force) models currently include point mass gravitational terms for all planets, the Sun and Moon, solar radiation pressure, finite maneuvers, and attitude maintenance activity modeled quadratically. In addition, observable errors due to troposphere are included. Further data types, force and observable models will be ncluded to enhance the accuracy of the models and the capability of the package. The heart of the ARSTSN is a currently available continuous-discrete extended Kalman filter. Simulated data used to test the implementation at various stages of development and the results from processing actual mission data are presented.

Burkhart, P. Daniel↗