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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 NTRS1980

X-ray bursters

The main properties of X-ray bursts, as well as the value of these bursts for understanding low-mass X-ray binaries, are discussed. The analysis of the X-ray spectrum of bursts during their decay has provided evidence that X-ray bursts arise from neutron stars. It is thus illustrated how observations of the X-ray bursts may be used to obtain information about the properties of neutron stars. In particular, a method for measuring the radii of neutron stars from observations of X-ray bursts is proposed, based on the results of the blackbody radii of X-ray bursters.

Van Paradijs, J.↗
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

Torques on a nearly rigid body in a relativistic gravitational field

The effect of post-Newtonian potentials on the rotation of a perfect fluid, nearly rigid body is shown to consist of a precession and a torque. The frequency of the precession can be exactly represented by means of suitable differential operators. The relativistic torques, in the quadrupole approximation, depend on the instantaneous orientation of the principal axes of one body with respect to the position - like the classical torque - and velocity of the other. For a relatively low-mass body, such as a gyroscope, these velocity-dependent torques have no observable consequences.

Caporali, A.↗
NASA NTRS1982

The evolution of highly compact binary stellar systems

A new theoretical treatment of the evolution of highly compact binary systems is presented. The evolution is calculated until almost the entire mass of the secondary has been transferred to the primary or lost from the system. It is assumed that gravitational radiation from the system is the cause of mass transfer. It is found that the structure of the mass-losing star can be approximated by an n = 3/2 polytrope, and as a result a relatively large number of different cases can be explored and some general conclusions drawn. An explanation is found for the existence of a cutoff in the orbital period distribution among the cataclysmic variables and light is shed upon the possible generic relationships among cataclysmic variables, the low-mass X-ray binaries, and the spectrally soft transient X-ray sources.

Rappaport, S.↗
NASA NTRS1982

Abell 2069 - An X-ray cluster of galaxies with multiple subcondensations

X-ray and optical observations of the cluster Abell 2069 are presented. The cluster is at a mean redshift of 0.116. The cluster shows multiple condensations in both the X-ray emission and in the galaxy surface density and, thus, does not appear to be relaxed. There is a close correspondence between the gas and galaxy distributions which indicates that the galaxies in this system do map the mass distribution, contrary to what might be expected if low-mass neutrinos dominate the cluster mass.

Gioia, I. M.↗
NASA NTRS1982

X-ray emission from young stars and implications for the early solar system

Recent observations of soft X-ray emission from solar-type stars obtained with the Einstein X-Ray Observatory indicate that X-ray luminosity is inversely correlated with stellar age. If this result is applied to the sun and if X-ray emission is a valid indicator of other manifestations of solar activity, then past solar wind and flare levels can be inferred. It can qualitatively explain the excess xenon and nitrogen found in the lunar regolith compared to the level expected from the contemporary solar wind. X-ray emission from T Tauri and other low-mass pre-main-sequence stars is both highly luminous and variable, indicating the presence of flares approximately 4000 times stronger than the largest flares seen in the contemporary sun. The proton flux from such solar flares during the one to ten million-year pre-main-sequence phase would be sufficient to account for the Al-26 anomaly in meteorites.

Feigelson, E. D.↗
NASA NTRS1984

Concentrator-Enhanced Solar Array

Deployable solar array for satellites uses slanted low-mass planar mirrors as walls of trough to triple light falling on GaAs solar cells forming bottom of trough. Power-to-mass ratio of new design 42 percent higher than planar array of same power output.

Morse, B. J.↗
NASA NTRS1984

Liquid-Droplet Radiative Cooler

Large-area, low-mass radiative cooler applicable to industrial processes requiring non-contacting cooling of process fluids. Droplet-stream radiators are used to radiate away waste heat. Extensive development required to produce practical system for terrestrial use. Effects of gravity and atmosphere are to be evaluated.

Knapp, K. K.↗
NASA NTRS1981

X-ray astronomy from Uhuru to HEAO-1

The nature of galactic and extragalactic X-ray sources is investigated using observations made with nine satellites and several rockets. The question of X-ray pulsars being neutron stars or white dwarfs is considered, as is the nature of Population II and low-luminosity X-ray stars, the diffuse X-ray emission from clusters of galaxies, the unidentified high-galactic-latitude (UHGL) sources, and the unresolved soft X-ray background. The types of sources examined include binary pulsars, Population II X-ray stars (both nonbursters and bursters) inside and outside globular clusters, coronal X-ray emitters, and active galactic nuclei. It is concluded that: (1) X-ray pulsars are strongly magnetized neutron stars formed in the evolution of massive close binaries; (2) all Population II X-ray stars are weakly magnetized or nonmagnetic neutron stars accreting from low-mass companions in close binary systems; (3) the diffuse emission from clusters is thermal bremsstrahlung of hot matter processed in stars and swept out by ram pressure exerted by the intergalactic gas; (4) most or all of the UHGL sources are active galactic nuclei; and (5) the soft X-ray background is emission from a hot component of the interstellar medium.

Clark, G. W.↗
NASA NTRS1983

Evolutionary effects of helium diffusion in population II stars

Evolutionary calculations continuing until well past turnoff are presented for models of low-mass Population II stars which take into account the effects of the diffusion of helium relative to hydrogen. Evolutionary tracks, cluster isochrones and hydrogen distributions were obtained for stellar masses in the range 0.75 to 1.01 solar masses, both in the presence and absence of diffusion. It is found that for a star of a given mass, diffusion speeds up the evolutionary process on the main sequence, although after turnoff evolution is slowed with respect to the case without diffusion. As the stars ascend the red giant branch, their outer regions are remixed so that evidence of helium diffusion is erased, and the evolutionary tracks of the models with and without diffusion converge. Thus, if the age of a globular cluster is determined from the absolute magnitude at turnoff or from fitting isochrones, diffusion results in a 25% reduction in the derived age at a turnoff magnitude of 4.23, and a 14% reduction at a turnoff magnitude of 3.45.

Stringfellow, G. S.↗
NASA NTRS1982

Fragmentation, protostellar winds, and star formation

Aspects of the current theory of molecular-cloud (MC) evolution and star formation are reviewed, with consideration of recent star and MC observations. The problem of MC collapse is discussed in terms of fragmentation in spherically symmetric collapse, the role of magnetic fields and density fluctuations, anisotropic collapse, and nonlinear interactions between fragments. Protostellar winds are identified as the source of the energy supporting MC against collapse, sweeping shells of mass into MC to produce low-mass stars continuously, and sustaining the production of massive stars once it is triggered by the collision of MCs, as in the spiral density-wave peaks. The clumping and coagulation processes are considered for the case of the MC in Orion. The protostellar-wind mass input required to inhibit systematic MC-core collapse is estimated at 10 to the -6th solar mass/cu pc year.

Silk, J.↗
NASA NTRS1983

The unique cometary nebula Parsamian 13

Parsamian 13 is found to be a cometary nebula, with a deeply embedded star suffering strong absorption by silicate grains. A feature near 2.7 microns, attributed to absorption by terminal OH groups, may represent the first detection in an astrophysical environment of water ice grains diluted by another molecule, for example by CO. The bolometric luminosity suggests that this star is either an extremely young T Tauri star or an evolved low-mass star, now a red giant, high on its convective track. Most unusual is the presence of cold (50 K) TiO gas in sufficient abundance to show in absorption in the optical and very near-infrared regions; this material probably represents very recently expelled photospheric layers.

Cohen, M.↗
NASA NTRS1983

X-ray observations of M33 with the high resolution imager on the Einstein Observatory

Three observations, separated by 6 months, of the Local Group galaxy M33 using the high resolution imager (HRI) on the Einstein Observatory are reported. Eight X-ray sources with luminosites ranging from 8 x 10 to the 36th to 1.2 x 10 to the 39th ergs/s have been detected. For seven of these sources, finding charts with positions accurate to less than 5 arcsec are provided. The X-ray properties and possible identifications are discussed for the eight HRI-detected sources and for two other sources, previously described by Long et al. (1981), for which upper limits are provided. It is found that most of the sources are associated with Population I markers. One source may be coincident with an optical supernova remnant. The most luminous source (by a factor of at least 25) is that associated with the optical nucleus. Because the X-ray flux from the nucleus decreased by a factor of 1/2 between the first and second observations, it is most likely that a single, compact object is responsible for the X-ray emission. It is possible that this source may be an active galactic nucleus, a massive binary X-ray source, or a low-mass X-ray binary such as are found in globular clusters within the Galaxy.

Markert, T. H.↗
NASA NTRS1983

A new technique for calculations of binary stellar evolution, with application to magnetic braking

The development of appropriate computer programs has made it possible to conduct studies of stellar evolution which are more detailed and accurate than the investigations previously feasible. However, the use of such programs can also entail some serious drawbacks which are related to the time and expense required for the work. One approach for overcoming these drawbacks involves the employment of simplified stellar evolution codes which incorporate the essential physics of the problem of interest without attempting either great generality or maximal accuracy. Rappaport et al. (1982) have developed a simplified code to study the evolution of close binary stellar systems composed of a collapsed object and a low-mass secondary. The present investigation is concerned with a more general, but still simplified, technique for calculating the evolution of close binary systems with collapsed binaries and mass-losing secondaries.

Rappaport, S.↗
NASA NTRS1984

Far-infrared studies of Herbig-Haro objects and their exciting stars

Far-infrared (40-160 micron) observations of Herbig-Haro objects and their probable exciting stars are presented. The importance of these far-infrared observations is epitomized by the fact that, on average, 70 percent of the bolometric luminosity of a typical candidate star is radiated beyond the longest detected ground-based wavelength, even for those objects observed out to 20 micron from the ground. Extended far-infrared emission characterizes some of these regions. Some Herbig-Haro nebulae are themselves conspicuous 100 micron peaks (e.g., HH 1 and HH 25). A bipolar structure is found at 100 micron in the vicinity of the Cohen-Schwartz star. All the exciting stars must be low-mass objects (approximately less than 3 solar mass). It is argued that they might be approximately 1 solar mass protostars still in their accretion phase.

Cohen, M.↗
NASA NTRS1984

Far-infrared observations of southern Herbig-Haro objects

Ground-based and airborne infrared observations are presented of the vicinities of several HH objects. New photographs of these HH nebulae have made it possible to locate the exciting stars of HH 46/47 and HH 57 from their infrared peak positions. Bolometric luminosities of the exciting stars lie in the range 4-12, consistent with those for low-mass accreting protostars.

Cohen, M.↗
NASA NTRS1984

Discovery of a 7.1 hour period and eclipses from MXB 1659-29

A 7.1 hr period has been discovered in the X-ray emission from the 'transient' X-ray burst source MXB 1659-29. Erratic variations in X-ray flux are seen during approximately 25 percent of the 7.1 hr cycle; at the end of this period, a stable dip in the flux occurs. Further analysis indicates that this dip is, in all probability, an eclipse by the companion star in the low-mass binary system. The short (about 15 minute) eclipse duration is used to refine the period determination (7.114104 + or - 0.000168 hr) and to constrain the companion star mass and binary system parameters. The companion star is found to be in the range 0.25-0.9 solar mass; probabilistic arguments and observations of cataclysmic variables with comparable periods indicate that the companion star is most likely less massive than the standard theories would indicate.

Cominsky, L. R.↗
NASA NTRS1984

High-resolution far-infrared observations of the extended W51 complex

A far-IR map with 1 arcmin resolution was obtained of the W51 H II region molecular cloud complex. The 40-120 microns survey was performed to study embedded sources which excite the H II gas. The far-IR emission distribution overlapped radio emissions from the region, implying that the extended dust clouds were heated by the same sources as the H II regions. Four compact sources were characterized and associated with concentrations of luminosities that suggested a scarcity of low-mass stars. The brightest source, labeled W51-I, has a luminosity/mass ratio of 150, high enough to indicate a burst of massive O star formation. No triggering mechanism was identified for the burst of star formation.

Rengarajan, T. N.↗