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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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Horizontal branch stars evolution based on mass distributions from comparison with giant branch, investigating evolutionary track characteristics during core helium burning
Main sequence and giant stars atmospheric structure models, noting metal deficiency effects
Positional and color magnitude data for 5116 stars are given.
The evolution of a Population I star of 15 solar masses is described from the carbon shell burning stage to the formation and collapse of an iron core. An unusual aspect of the evolution is that neon ignition occurs off-center and neon burning propagates inward by a series of shell flashes. The extent of the core burning is generally smaller than the Chandrasekhar mass, so that most of the nuclear energy generation occurs in shell sources. Because of degeneracy and the influence of rapid convective mixing, these shell sources are unstable and the core goes through large excursions in temperature and density. The small core also causes the shell sources to converge into a narrow mass region slightly above the Chandrasekhar mass. Thus, the final nucleosynthesis yields are generally small, with silicon being most strongly enhanced with respect to solar system abundances.
A number of spectroscopic peculiarities of K giants and other stars which lie in a wedge in the HR diagram are discussed. These peculiarities can be understood in terms of unsteady magnetic flux loops emerging into the stellar atmosphere from beneath the surface.
A semiempirical modeling of stellar chromospheres is extended to late-type supergiants, where computations match high-resolution, absolute-flux profiles of the Ca II K and Mg II h and k lines. IUE UV spectra of Epsilon Gem and Alpha Ori show no evidence of emission lines formed at temperatures greater than 10,000 K, leading to the computation of chromospheric models extending to 10 to the -6th g/sq cm at temperatures that rise to 6500 K for the former star and 7000 K for the latter. By contrast, the C II-IV, Si IV, and He II and N V strong emission lines of Beta Dra lead to a tentative chromospheric model extension to 16,000 K at 0.012 dynes/sq cm. It is pointed out that the Ca II and Mg II line analyses presented, which assume hydrostatic equilibrium with only thermal and turbulent components to the pressure, imply nearly plane-parallel chromospheres even in the case of Alpha Ori.
Results of a computer search for occultations of AGK3 and SAO stars by 91 of the larger asteroids are presented. Thirty-eight events occurring in 1982 and 39 in 1983 are identified. Nominal ground tracks are plotted for the more promising occultations.
IUE low-dispersion spectra and spectral scans made with the Lick Observatory IDS scanners have been combined for 16 shell stars. Eleven objects can be represented by Kurucz (1979) model atmospheres, although some of them display strong shell-type line spectra. Five among them are known binaries. The six remaining objects display complex spectra. A model involving continuum and line radiation from a hydrogen cloud surrounding the accreting component is proposed. A generalization of this model with optically thick segments of the cloud promises to explain even more exotic objects such as beta Lyrae, W Serpentis and possibly epsilon Aurigae.
Occultations of stars fainter than the AGK and SAO catalog limits by selected minor planets during their 1983 apparitions have been identified by scanning plates taken with the 13-in. Lowell astrograph. A total of 33 upcoming occultations have been found involving 1 Ceres, 10 Hygiea, 52 Europa, 65 Cybele, 451 Patientia, 511 Davida, and 704 Interamnia.
The STAR system developed by NASA enables any user with a logic diagram to design a semicustom digital MOS integrated circuit. The system is comprised of a library of standard logic cells and computer programs to place, route, and display designs implemented with cells from the library. Library cells of the CMOS metal gate and CMOS silicon gate technologies were simulated using SPICE, and the results are shown and compared.
Results of Einstein X-ray observations of 25 stellar systems are presented. The systems observed include 15 spectroscopic binaries of which eleven were detected; nine were serendipitous detections, three of which may be new RS CVn systems. Coronal activity levels and their implications for these stars are discussed.
Wind models using the recent improvements of radiation driven wind theory by Pauldrach et al. (1986) and Pauldrach (1987) are presented for central stars of planetary nebulae. The models are computed along evolutionary tracks evolving with different stellar mass from the Asymptotic Giant Branch. We show that the calculated terminal wind velocities are in agreement with the observations and allow in principle an independent determination of stellar masses and radii. The computed mass-loss rates are in qualitative agreement with the occurrence of spectroscopic stellar wind features as a function of stellar effective temperature and gravity.
Shear moduli are calculated for bcc crystalline and rapidly quenched Coulomb solids produced by the Monte Carlo simulation method. The shear moduli are calculated up to the transition temperature and include the effects of thermal fluctuations. An effective shear modulus appropriate to an approximate 'isotropic' body is introduced. It is found that the values of the 'average shear modulus' for the quenched solids remain about the same as those for the corresponding bcc crystals, although the individual shear moduli of the former, disordered solids deviate considerably from the cubic symmetry of the latter. These results are applied to analyses of neutron star oscillations. It is found that the periods of the two interfacial modes are increased by about 10 percent compared to previous results, and that s-mode periods are increased by about 30 percent. The periods of the f and p modes are hardly affected at all. The surface g-mode periods are not greatly affected, while the t-mode periods are increased by 20-25 percent.
The missions planned for the 1990's will greatly expand the knowledge of close binary systems and the physical phenomena that can be studied in a member of a close binary, from stellar active regions to the highest density black hole candidates known. These systems and the phenomena are reviewed with reference to major outstanding questions, the expected capability to answer them, and the expansion of capability that would be necessary. A 'super' XMM or LAMAR experiment with larger area, but similar moderate energy resolution and moderate spatial resolution, could detect 0.1 millisecond bursts from Cyg X-1 and 1 millisecond bursts in quiescent black hole candidates, measure Doppler and gravitational energy shifts in the iron line features for black holes and neutron stars. It would also identify these objects in galaxies a few Mpc away and open the way for evolution studies. A somewhat less ambitious goal would be high energy resolution of about the area of LAMAR to make full use of the information in the emission lines in both normal and compact binaries.
An updated and improved NASA spacecraft attitude determination catalog, now called SKY2000, Version 3, has been prepared and quality assured. The highest priority goals were to replace the astrometric (positions and motions) and photometric (brightnesses and colors) data with the most recent and accurate data available. Quality assurance has been performed in a fairly straightforward manner, i.e., without extensive data checking and analysis, and many errors and Inconsistencies were corrected. Additional work should eventually be done on the variability and multiple-star data In the catalog, while certain other data can be significantly Improved. The current version of the catalog can be found at the GSFC Flight Dynamics website: http://cheli.gsfc.nasa.gov/dist/attitude/skymap.html. Supporting information and reference materials (published papers, format and data descriptions, etc.) can also be found at the website.
The goal of the project is to analyze the spectra of the most massive stars in our neighbor Galaxies, to determine the physical parameters of temperature, mass, gravity, and Luminosity, together with the stellar wind properties. For this purpose, FUSE spectra, HST spectra (uv and optical) and high quality optical spectra obtained with ground-based telescopes need to be analyzed wing modern NLTE model atmosphere techniques. The combination of the use of spectra from different wavelength regions is a fundamental aspect of the project. Each spectral domain adds complementary important to the process of the spectral analysis. In this way the comparison of stellar properties between galaxies of different metallicity will become more significant.
The research conducted during the reporting period is grouped into three sections: 1) Warm molecular gas in the interstellar medium (ISM); 2) Absorption line studies of "cold" molecular clouds; 3) Vaporization of comets around the AGB star IRC+10216.
In Papers I and II in this series, we presented hydrodynamical simulations of jet models with parameters representative of the symbiotic system MWC 560. These were simulations of a pulsed, initially underdense jet in a high-density ambient medium. Since the pulsed emission of the jet creates internal shocks and since the jet velocity is very high, the jet bow shock and the internal shocks are heated to high temperatures and should therefore emit X-ray radiation. In this paper, we investigate in detail the X-ray properties of the jets in our models. We have focused our study on the total X-ray luminosity and its temporal variability, the resulting spectra, and the spatial distribution of the emission. Temperature and density maps from our hydrodynamical simulations with radiative cooling presented in the second paper are used, together with emissivities calculated with the atomic database ATOMDB. The jets in our models show extended and variable X-ray emission, which can be characterized as a sum of hot and warm components with temperatures that are consistent with observations of CH Cyg and R Aqr. The X-ray spectra of our model jets show emission-line features that correspond to observed features in the spectra of CH Cyg. The innermost parts of our pulsed jets show iron line emission in the 6.4-6.7 keV range, which may explain such emission from the central source in R Aqr. We conclude that MWC 560 should be detectable with Chandra or XMM-Newton, and such X-ray observations will prove crucial for understanding jets in symbiotic stars.