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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
Three Sun-mass star evolution from main sequence to helium exhaustion in core, noting chronology of process
Evolution of giant star from helium ignition through helium exhaustion - astrophysics
We present the results of N-body simulations of tidally limited star clusters with an initial population of 0%-20% binaries. We find that (1) if enough binaries are initially present, the binary fraction may fall to a minimum value, then increase at late times; (2) the cluster evaporation timescale is quite insensitive to the details of the initial binary distribution; (3) the cluster core radius stabilizes at a few percent of the half-mass radius when binaries are present, just as in the case of isolated clusters; and (4) there may be a marked difference between the spatial distribution of low-energy and high-energy binaries as the cluster evolves. Specifically, the spatial distribution of the lower energy systems is often substantially more extended than that of the more tightly bound pairs. At no time are our simulated clusters well described by simple dynamical models that neglect the close coupling between the binding energies and the center-of-mass energies of the binaries they contain.
UV dwarf star evolution, using central and gap star models emphasizing photoneutrino emission
Various papers on solar science are presented. The optics considered include: variability of solar irradiance, sunspot number, solar diameter, and solar wind properties; theory of luminosity and radius variations; standard solar models; the sun and the IMF; variations of cosmic-ray flux with time; accelerated particles in solar flares; solar cosmic ray fluxes during the last 10 million yrs; solar neutrinos and solar history; time variations of Be-10 and solar activity; solar and terrestrial components of the atmospheric C-14 variation spectrum; solar flare heavy-ion tracks in extraterrestrial objects. Also addressed are: the faint young sun problem; atmospheric responses to solar irradiation; quaternary glaciations; solar-terrestrial relationships in recent sea sediments; magnetic history of the sun; pre- and main-sequence evolution of solar activity; magnetic activity in pre-main-sequence stars; classical T Tauri stars; relict magnetism of meteorites; luminosity variability of solar-type stars; evolution of angular momentum in solar-mass stars; time evolution of magnetic fields on solarlike stars.
Stellar evolution for star of 30 solar masses during helium ignition, depletion and exhaustion
X-ray lasers have evolved from a Star Wars missile defense system to a table-top research tool: (1) LLNL proposes X-ray laser schemes in the 1970’s, (2) First X-ray lasers demonstrated in early 1980’s were nuclear pumped, (3) Demonstrated the world’s shortest wavelength, highest energy laser, (4) First laboratory X-ray laser demonstrated on Novette in 1984, (5) A decade of progress using the Nova laser (5 kJ) from 1985 to 1996, (6) X-ray lasers produced at the COMET table-top facility (<10 J) since 1997, (7) X-ray lasers used for plasma interferometry and other applications, (8) 10 Hz X-ray laser at 18.9 nm demonstrated in 2004 using 0.15 J drive, (9) 100 Hz X-ray laser at 13.9 nm produces 1 µJ of saturated output using 0.9 J drive from diode-pumped optical laser in 2014.
Evolutionary models in early and main sequence stages for low mass stars, using Hertzsprung- Russell diagram
Polytropic premain-sequence evolutionary tracks and main sequence models of solar composition low mass stars
We present a three-dimensional numerical study of tidal disruption of a main-sequence star by a supermassive black hole. The simulations include general relativistic effects which are important in this regime. We analyze stars in a marginally bound orbit around the black hole with pericentric separation of a few Schwarzschild radii. We show that during a close passage, as a result of relativistic effects analogous to the perihelion shift, the trajectories of the debris of the star fan out into a crescent-like shape centered on the black hole. We also discuss the increase of the central density of the star as it approaches pericentric distance, the fraction of the debris accreted by the hole, its accretion rate, the distribution of debris orbits bound to the hole, and the velocity of unbound ejected material. We compare these results with the disruption of the star by a Newtonian point mass.
We consider the interrelationships among the structure of molecular clouds; the collapse of rotating cloud cores; the formation of stars and disks; the origin of molecular outflows, protostellar winds, and highly collimated jets; the birth of planetary and binary systems; and the dynamics of star/disk/satellite interactions. Our discussion interweaves theory with the results of observations that span from millimeter wavelengths to X-rays.
New optical observations of the central star of the planetary nebula IRAS 18333-2357 in the globular cluster M22 show lines of H I, He II, C IV, N IV, and N V. The spectrum closely resembles the sdO star KS 292, which has surface abundances enhanced by products of hydrogen shell burning and helium burning, and an effective temperature of 75,000 K. The lines of C in IRAS 18333-2357 seem somewhat stronger than in KS 292, and the lines of N are considerably stronger. The presence of substantial hydrogen is surprising in view of the hydrogen-poor nature of the nebular ejecta. If IRAS 18333-2357 is as hot as its analog, its luminosity is about 14,000 lunar luminosity. This value is higher than that theoretically expected for single-star evolution of M22 cluster stars.
This review outlines the observational properties of young stellar objects as they evolve from their birth within dense rotating molecular cores to fully-formed pre-main sequence stars. Current work suggests that most of the mass which ultimately comprises a fully-formed star is transferred from a flattened infalling envelope (of size approximately several thousand AU) through a circumstellar accretion disk to the stellar surface. We summarize current estimates for the duration of the envelope infall and disk accretion phases and discuss the implication of these timescales for the formation of stars of different mass and of planetary systems.
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In standard stellar evolution, stars with masses ranging from approximately 150 to 240M ⊙ are expected to evolve to a pair instability supernova with no black hole (BH) remnant. This evolutionary behavior leads to a predicted gap in the black hole mass function from approximately 50 to 140M ⊙ . Yet the LIGO and Virgo Collaborations recently discovered black holes of masses 66M ⊙ and 85M ⊙ in the gravitational wave event GW190521. Here, we propose a new method to populate the BH mass gap. If an energy source is added throughout the star in addition to nuclear fusion, it is possible for the altered evolution to avoid the complete destruction of a pair instability supernova, and instead a BH remnant is left behind. An example of an extra energy source is dark matter annihilation within the star, but our results hold more generally. We show this phenomenon by exploring the effect of adding an energy source independent of temperature and density to a 180M ⊙ star, using the MESA one-dimensional stellar evolution software. If ~50% of the star’s energy is due to this new source, the star is capable of avoiding the pair instability entirely and evolving towards a core-collapse supernova and ultimately a BH remnant with mass ~ 120M ⊙ .
Evolution of o stars - hydrogen exhaustion and gravitational contraction
The paper investigates the evidence for the two interpretations of Wolf-Rayet stars suggested in the literature: (1) massive premain-sequence stars with disks and (2) massive stars which have lost most of their H-rich layers in a stellar wind is investigated. The abundance determinations which are done in two different ways and which lead to different conclusions are discussed. The composition is solar, which would suggest interpretation (1), or the CNO abundances are strongly anomalous, which would suggest interpretation (2). Results from evolutionary calculations, stellar statistics, the existence of Ofpe/WN9 transition stars and W-R stars with evolved companions show overwhelming evidence that W-R stars are not premain-sequence stars but that they are in a late stage of evolution. Moreover, the fact that W-R stars are usually in clear regions of space, whereas massive premain-sequence stars are embedded in ultracompact H II regions also shows that W-R stars are not young premain-sequence stars.