A GRB model satisfying stringent observational constraints

The temporal behavior of GRBs is quantified using a power spectrum analysis. The power spectrum of great variety of GRBs is well represented by the simple ^–2 behavior. We then study a cosmological GRB model in which relativistic flows interact with dense radiation fields. This mechanism in the densest stellar regions known to exist, surprisingly yields the correct temporal behavior. Other characteristics are also reproduced, including the duration bimodality and the hardness-duration distribution.     

The Porous Atmosphere of eta Carinae

We analyze the wind generated by the great 20 yr-long super-Eddington outburst of eta Carinae. We show that by using the classical stellar atmosphere and wind theory, it is impossible to construct a consistent wind model in which a sufficiently small amount of mass, like the one observed, is shed. One expects the super-Eddington luminosity to drive a thick wind with a mass-loss rate substantially higher than the observed one. The easiest way to resolve the inconsistency is if we alleviate the implicit notion that atmospheres are homogeneous. An inhomogeneous, or "porous," atmosphere allows more radiation to escape while exerting a smaller average force. Consequently, such an atmosphere yields a considerably lower mass-loss rate for the same total luminosity. Moreover, all the applications of the Eddington luminosity as a strict luminosity limit should be revised or at least reanalyzed carefully.     

On the interaction between the URCA process and convection

The influence of the URCA process (β-decay, electron capture) on convective stability is investigated and a stability criterion is derived. The criterion contains the Schwarzschild criterion and the thermohaline convection. It is found that URCA may cause convective instability to an otherwise stable medium, but it cannot stabilize an unstable medium, only the growth rate is affected. A numerical example for the Na²³?Ne²³ URCA pair shows the regions in the ?-T plane where instability is caused (assuming given abundances of the isotopes). The evolution of C-O core of an evolved 3.5M _⊙–8M _⊙ star may be affected by formation of convective regions even prior to C¹² ignition.     

Implosions and emplosions in supermassive objects

It is shown that for small velocities the time dependent evolution of massive stars may be described by a series of static models. Those are linked to each other by one continuous time dependent parameter-the relativity effect. The fate of the dynamic system is analyzed by the behaviour of the static models. The method is illustrated for general relativistic polytropes.     

The evolution of 1.40M θ pure He star

The evolution of 1.40M pure He star is calculated from the stage of the ignition in the center up to the very advanced stage of evolution where mass ejection by the very luminous He shell could occur. It is found that C¹² does not ignite by a modest margin. Subsequent evolution and relation to the central stars of planetary nebulae is discussed.     

The extragalactic neutrino background radiations from blazars and cosmic rays

Blazar emission of gamma rays and cosmic ray production of gamma rays in gas-rich clusters have been proposed recently as alternative sources of the high energy extragalactic diffuse gamma ray background radiation. We show that these sources also produce very different high energy extragalactic diffuse neutrino background radiations. An extragalactic neutrino background radiation may be detected by the new generation of large neutrino telescopes under construction and may be used to trace the origin of the extragalactic gamma radiation.     

Low-mass red giants and masses of NPNs

The evolutionary track of low-mass red giant stars (0.7–0.9M ) is computed with the aim to demonstrate the conditions under which low-mass white dwarfs (WDs) can form through the evolution of single stars. Also, the influence of the mixing length to the scale height ratio on the radius of the star is calculated and the coupling between the mixing-length and the mass-loss rate parameters is investigated. Our conclusions are that the uncertainties in mass-loss and mixing-length to scale-height ratio leave enough parameter space to allow the formation of low-mass WD via single star evolution. We also conclude that the gap between proto-WD stars without any nebula and stars with well-defined nebulae is bridged by stars which have a dilute gas cloud around them which cannot be observed as a nebula.     

Critical parameters for supermassive objects in general relativity

Evolutionary tracks up to the point of dynamical instability are obtained for isentropic objects with rest masses ranging from 10² M to 10⁷ M . Accurate values for the red shift, specific entropy, luminosity and effective temperature at the onset of collapse are given.     

Dynamic phases in the evolution of a 1.25M ⊙ C−O star

The evolution of a 1.25M _⊙ carbon and oxygen (equal fractions by mass) homogeneous star is followed by means of a computer code capable of dealing with dynamic evolutionary phases. After carbon ignition at the center, followed by successive shell flashes and the formation of aT-inversion, convection begins at the surface and the model evolves through a very short but strong dynamic phase (viz. a pulsation) after which it settles down to a white dwarf configuration.