1,490 research outputs found
Radiation from hot bare strange stars
We present the results of numerical simulations of stationary, spherically
outflowing, pair winds, with total luminosities of L=10^{35}- 10^{42} ergs/s.
These results have direct relevance to the emission from hot, bare, strange
stars, which are thought to be powerful sources of electron-positron pairs
created by the Coulomb barrier at the quark surface. The spectra of emergent
photons and pairs are calculated. For L > 2x10^{35} erg/s, photons dominate the
emerging emission. As L increases from 10^{35} to 10^{42} ergs/s, the mean
photon energy decreases from ~ 400-500 keV to 40 keV, while the spectrum
changes in shape from a wide annihilation line to being nearly blackbody with a
high energy (> 100 keV) tail. Such a correlation of the photon spectrum with
the luminosity, together with the fact that super-Eddington luminosities can be
achieved, might be a good observational signature of hot, bare, strange stars.Comment: 4 pages, 4 figures, Accepted in MNRAS, includes minor correction
Pair Winds in Schwarzschild Spacetime with Application to Strange Stars
We present the results of numerical simulations of stationary, spherically
outflowing, electron-positron pair winds, with total luminosities in the range
10^{34}--10^{42} ergs/s. In the concrete example described here, the wind
injection source is a hot, bare, strange star, predicted to be a powerful
source of pairs created by the Coulomb barrier at the quark surface. We find
that photons dominate in the emerging emission, and the emerging photon
spectrum is rather hard and differs substantially from the thermal spectrum
expected from a neutron star with the same luminosity. This might help
distinguish the putative bare strange stars from neutron stars.Comment: 3 pages, 2 figures, Invited talk at 11th Marcel Grossmann Meeting,
Berlin, July 200
A Two-Dimensional Hydrostatically Equilibrium Atmosphere of a Neutron Star with Given Differential Rotation
An analytic solution has been found in the Roche approximation for the
axially symmetric structure of a hydrostatically equilibrium atmosphere of a
neutron star produced by collapse. A hydrodynamic (quasione-dimensional) model
for the collapse of a rotating iron core in a massive star gives rise to a
heterogeneous rotating protoneutron star with an extended atmosphere composed
of matter from the outer part of the iron core with differential rotation
(Imshennik and Nadyozhin, 1992). The equation of state of a completely
degenerate iron gas with an arbitrary degree of relativity is taken for the
atmospheric matter. We construct a family of toroidal model atmospheres with
total masses and total angular momenta , which are acceptable for the
outer part of the collapsed iron core, in accordance with the hydrodynamic
model, as a function of constant parameters of the
specified differential rotation law in spherical
coordinates. The assumed rotation law is also qualitatively consistent with the
hydrodynamic model for the collapse of an iron core.Comment: 9 pages, 6 figures, 1 tabl
Electrophilically Activated Nitroalkanes in Synthesis of 3,4-Dihydroquinozalines
Nitroalkanes activated with polyphosphoric acid serve as efficient electrophiles in reactions with various nucleophilic amines. Strategically placed second functionality allows for the design of annulation reactions enabling preparation of various heterocycles. This strategy was employed to develop an innovative synthetic approach towards 3,4-dihydroquinazolines from readily available 2-(aminomethyl)anilines
A Convenient Way to Quinoxaline Derivatives through the Reaction of 2-(3-Oxoindolin-2-yl)-2-phenylacetonitriles with Benzene-1,2-diamines
Microwave-assisted reaction between 2-(3-oxoindolin-2-yl)-2-phenylacetonitriles andbenzene-1,2-diamines leads to the high-yielding formation of the corresponding quinoxalines as sole, easily isolaable products. The featured transformation involves unusual extrusion of phenylacetonitrile molecule and could be performed in a short sequence starting from commonly available indoles and nitroolefins
Improved Method for Preparation of 3-(1H-Indol-3-yl)benzofuran-2(3H)-ones
3-(1H-Indol-3-yl)benzofuran-2(3H)-ones were efficiently accessed via polyphosphoric acid-mediated condensation of 3-(2-nitrovinyl)-1H-indoles with phenols
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