Astrophysics
A comparison is made between the properties of CAL 83, CAL 87, RX J0513.9-6951, 1E 0035.4-7230 (SMC 13), RX J0019.8+2156, and RX J0925.7-4758, all supersoft X-ray binaries. Spectra with the same resolution and wavelength coverage of these…
We report on Westerbork 1.4 GHz radio observations of the radio counterpart to $\gamma$-ray burst GRB~970508, between 0.80 and 138 days after this event. The 1.4 GHz light curve shows a transition from optically thick to thin emission…
The possibility of a neutron m=2-superfluid in the interior of neutron stars is investigated. This pairing state is energetically favoured in strong magnetic fields ($H\sim 10^{16}-10^{17}$ G). Because of the node in the angular-dependent…
We present a new determination of the mass function of galaxy clusters, based on optical virial mass estimates for a large sample of 152 nearby (z\le0.15) Abell-ACO clusters, as provided by Girardi et al. (1998). This sample includes both…
We describe planetesimal accretion calculations in the Kuiper Belt. Our evolution code simulates planetesimal growth in a single annulus and includes velocity evolution but not fragmentation. Test results match analytic solutions and…
We present the results of the observations of the giant bursts from the X-ray pu lsar A0535+26 made by HEXE onboard Mir-Kvant in April 1989, November 1993 and February 1994. The pulse periods were measured, pulse profiles in different…
A one-dimensional turbulent convection model in the form of a time-dependent diffusion equation for the turbulent energy is incorporated into our numerical pulsation code. The effect of turbulent convection on the structural rearrangement…
Galaxy evolution depends strongly on the environment. Dynamical interactions and subsequent evolution make galaxies more concentrated, with higher surface densities, and also trigger star-formation, which consumes the available cold gas.…
The numerical hydrodynamic modelling of beat Cepheid behavior has been a longstanding quest in which purely radiative models have failed miserably. We find that beat pulsations occur naturally when turbulent convection is accounted for in…
We estimate the evolution of the contribution of galaxies to the cosmic background flux at $912 \AA$ by means of a semi-analytic model of galaxy formation and evolution. Such a modelling has been quite successful in reproducing the optical…
How much matter is there in the universe? Does the universe have the critical density needed to stop its expansion, or is the universe underweight and destined to expand forever? We show that several independent measures, especially those…
In the interstellar medium, as well as in the Universe, large density fluctuations are observed, that obey power-law density distributions and correlation functions. These structures are hierarchical, chaotic, turbulent, but are also…
We consider magnetic field evolution of neutron stars during polar-cap accretion. The size of the polar cap increases as the field decays, and is set by the last open field line before the accretion disk. Below the polar cap we find the…
Annihilation of high energy, $\sim 10^{21}$eV, neutrinos on big bang relic neutrinos of $\sim 1$eV mass, clustered in the Galactic halo or in a nearby galaxy cluster halo, has been suggested to generate, through hadronic Z decay, high…
We investigate the dynamics and radiation from a relativistic blast-wave which decelerates as it sweeps up ambient matter. The bulk kinetic energy of the blast-wave shell is converted into internal energy by the process of accreting…
The shape of the radial velocity and light curves of 24 long-period (30 < P < 134 days) Cepheids in the Magellanic Clouds shows a progression with the period. The sequences of the radial velocity and light curves are based only on a small…
We describe a method of determining the system parameters in non-eclipsing interacting binaries. We find that the extent to which an observer sees the shape of the Roche-lobe of the secondary star governs the amount of distortion of the…
We present radio continuum observations of the spiral-shaped ionized feature (Sgr A West) within the inner pc of the Galactic center at three epochs spanning 1986 to 1995. The VLA A-configuration was used at $\lambda$2cm (resolution of…
We define a complete sample of thirty-three GHz-Peaked-Spectrum (GPS) radio sources based on their spectral properties. We present measurements of the radio spectra and polarization of the complete sample and a list of additional GPS…
We show that there is a relationship between the age excess, defined as the difference between the stellar isochrone and chromospheric ages, and the metallicity as measured by the index [Fe/H] for late-type dwarfs. The chromospheric age…