Astrophysics
We present a calculation of a neutrino decay scenario in the early Universe. The specific decay is \nu_{2} \to \nu_{1} + \phi, where \phi is a boson. If there is a neutrino mass hierarchy, m_{\nu_{e}} < m_{\nu_{\mu}} < m_{\nu_{\tau}}, we…
The Gunn g, r and i CCD images of a representative sample of 17 Brightest Cluster Galaxies (BCM) have been analyzed in order to derive surface brightness and color profiles, together with geometrical parameters like eccentricity and…
Measurements by the U.C. Berkeley Infrared Spatial Interferometer at 11.15 micron have yielded strong evidence for multiple dust shells and/or significant asymmetric dust emission around NML Cyg. New observations reported also include…
There has been some controversy over the expression for the so-called `interaction energy' due to screening of charged particles in a plasma. Even in the relatively simple case of weak screening, first discussed in the context of…
We present a model for the high-low state transition of the X-Ray Nova GS 1124-68 (Nova Muscae 1991) observed by Ginga. The model consists of an advection-dominated accretion flow (ADAF) near the central black hole surrounded by a thin…
We investigate the hypothesis that $\lyal$ absorption lines arise in two populations of halos --- minihalos of small circular velocity ($V_c \la 55$ km s$^{-1}$) in which star formation and metal production are inhibited by photoionization…
We report results of RXTE observations of PSR B1951+32 using the PCA instrument for 19k seconds during 1996 March 24th. We applied the contemporaneous radio ephemeris and various statistical tests to search for evidence of pulsation. These…
The dependence of the number density of the bright QSOs at different redshifts ($n_{QSO}(z)$) on initial power spectrum is studied. It is assumed that QSO phenomenon is an early short term stage of evolution of massive galaxies with $M\geq…
We present a detailed review of large-scale structure (LSS) study using the discrete wavelet transform (DWT). After describing how one constructs a wavelet decomposition we show how this bases can be used as a complete statistical…
Hot (explosive) hydrogen burning or the Rapid Proton Capture Process (rp-process) occurs in a number of astrophysical environments. Novae and X-ray bursts are the most prominent ones, but accretion disks around black holes and other sites…
The structural properties of elliptical galaxies are consistent with their formation in a merging hierarchy. In this picture, the role of gaseous processes and dissipation decreased with increasing mass creating preferentially rotationally…
We discuss general relativistic effects in the steady-state neutrino-driven ``wind'' which may arise from nascent neutron stars. In particular, we generalize previous analytic estimates of the entropy per baryon $S$, the mass outflow rate…
A numerical integration is made, starting with a Kantowski-Sachs (KS) model with an added initial perturbation at time one-tenth the age of the universe, and evolving up to the present. According to a prediction by Barrow (1989), the ratio…
We present a combined, non-simultaneous, ASCA GIS and CGRO OSSE spectrum of the Seyfert 2 galaxy, NGC 7172, and make broad band spectral fits. The only Seyfert 2 galaxy previously studied over such a broad band is NGC 4945. We find that the…
One way of recovering information about the initial conditions of the Universe is by measuring features of the cosmological density field which are preserved during gravitational evolution and galaxy formation. In this paper we study the…
Study of gravitational-radiation induced merging rates of relativistic binary stars (double neutron stars; neutron star + black hole; double black holes) shows that the first-generation gravitational wave interferometers with an…
Dynamical friction and tidal disruption are effective mechanisms of evolution of globular cluster systems, especially in non-axysimmetric galaxies with a central compact nucleus. With a semi-analytical approach based on the knowledge of the…
We find that a non-axisymmetric bow shock model, with an appropriate choice of parameters, could fit the line splitting velocity field of the cone-like H$\alpha$ nebula in NGC 4945 better than a canonical cone model. Meanwhile, the bow…
We describe PTreeSPH, a gravity treecode combined with an SPH hydrodynamics code designed for massively parallel supercomputers having distributed memory. Our computational algorithm is based on the popular TreeSPH code of Hernquist & Katz…
Interstellar dust models are facing a "carbon crisis", so called because recent observations suggest that the abundance of carbon available for dust in the interstellar medium is less than half of the amount required to be tied up in…