Astrophysics
We study the evolution with redshift of the number density of Ly$\alpha$ clouds in a CDM model using numerical simulations including photo-ionization and cooling of the baryonic component. The photo-ionizing flux is consistently taken as…
Real-time detection of microlensing has moved from proof of concept in 1994 to a steady stream of events this year. Global dissemination of these events by the MACHO and OGLE collaborations has made possible intensive photometric and…
Recently, the observed cellular nature of the large-scale structure of the Universe with its quasi-regular pattern of superclusters and voids has been pointed out by several authors. In this paper, we investigate properties of the initial…
We present BV CCD-data for 11 intermediate-age LMC clusters; the main conclusions are: 1. in the (V_to, V_cl,m) and (V-to, (V_to-V_cl,m)) planes the models yield a good overall description of the data; 2. with the current sample, it is…
We study a sample of 62 Baade's Window (1,-4) K giants that have published proper motions, radial velocity and metallicity. We construct the velocity ellipsoids for the metal rich stars and metal poor stars. We find a vertex deviation…
We provide the mathematical framework which elucidates the way of using a Tully-Fisher (TF) like relation in the determination of the Hubble constant $H_0$, as well as for distances of galaxies. The methods related to the so-called Direct…
We report the successful development and operation of a large astronomical liquid-mirror telescope. Employing a rotating 2.7-meter diameter mirror with a surface of liquid mercury, the telescope images a half-degree diameter field centered…
We investigate the impact of hierarchical galaxy merging on the statistics of gravitational lensing of distant sources. Since no definite theoretical predictions for the merging history of luminous galaxies exist, we adopt a parametrized…
Recent high energy gamma-ray observations (E>100 MeV) of blazar AGN show emission spectra with no clear upper energy cutoff. AGN, considered to be possible sources for the highest energy cosmic rays, may have emission extending well into…
We derive lithium abundances in 53 T Tauri stars (TTS), concentrating on weak-line TTS. Our study gives the following results: 1)At luminosities $\ge 0.9 L\sun$ the Li abundances are remarkably uniform, with a mean value, log~N(Li)=3.1,…
We consider charged boson stars and study their effect on the structure of the vacuum. For very compact particle like ``stars", with constituent mass $m_{*}$ close to the Planck mass $m_{Pl}$, i.e. $m_{*}^{2} = {\cal O} (\alpha…
It is suggested that the nonorthodox model of a quasar as a neutrino ball described in terms of the standard model extended by adding right-handed neutrinos and the Majorana scalar field can be presented in order to explain a quasar as a…
We report our measurement of the rate of change of period with time dP/dt for the 215 s periodicity in the pulsating white dwarf G 117-B15A, the most stable optical clock known. After 31 years of observations, we have finally obtained a 4…
In this Letter, we present the initial characterization of extragalactic 24um sources in the Spitzer First Look Survey (FLS) by examining their counterparts at 8um and R-band. The color-color diagram of 24-to-8 vs. 24-to-0.7um is populated…
We analyze OGLE-2003-BLG-262, a relatively short, t_E=12.5+-0.1day, microlensing event generated by a point-mass lens transiting the face of a K giant source in the Galactic bulge. We use the resulting finite-source effects to measure the…
The Engineering Array of the Auger Observatory has been running successfully since 2001 and inclined showers have been recorded from the start. We have analysed the events with zenith angle $>$ 70$^0$ recorded between May and November 2002.…
Multi-fiber spectroscopy has been obtained for 335 galaxies in the field of the double cluster A3128/A3125, using the 2dF multi-fiber positioner on the AAT. A total of 532 objects in the double cluster now have known redshifts. We have also…
We have recently discovered a forming cluster around the radio galaxy MRC 1138-262 at redshift 2.2. Besides the population of Ly alpha emitting galaxies that have been confirmed spectroscopically, we have detected many candidate H alpha…
High resolution X-ray spectra of very young massive stars opened a new chapter in the diagnostics and understanding of the properties of stellar wind plasmas. Observations of several very young early type stars in the Orion Trapezium…
We simulate the characteristics of the Galactic population of radio and $\gamma$-ray pulsars using Monte Carlo techniques. At birth, neutron stars are spatially distributed in the Galactic disk, with supernova-kick velocities, and randomly…