Astrophysics
Although it is commonly agreed that the presence of a close stellar companion is likely to affect planet formation and evolution, the precise effects and their actual impact on planet occurrence and properties are still debated. In…
We model the evolution of protoplanetary disks surrounding millisecond pulsars, using PSR 1257+12 as a test case. Initial conditions were chosen to correspond to initial angular momenta expected for supernova-fallback disks and disks formed…
We present XMM-Newton observations of the eclipsing polar V2301 Oph which cover nearly 2.5 binary orbital cycles and 2 eclipses. This polar is believed to have the lowest magnetic field strength (7 MG) of any known polar. We find evidence…
It is well established that mass loss from AGB stars due to dust driven winds cannot be arbitrarily low. We model the mass loss from carbon rich AGB stars using detailed frequency-dependent radiation hydrodynamics including dust formation.…
We study the survival of substructures (clumps) within larger self-gravitating dark matter halos. Building on scaling relations obtained from N-body calculations of violent relaxation, we argue that the tidal field of galaxies and halos can…
We present a purely theoretical study of the morphological evolution of self-gravitating systems formed through the dissipationless collapse of N-point sources. We explore the effects of resolution in mass and length on the growth of…
We present the results of a uniform analysis of the soft X-ray spectra of fifteen type I AGN observed with the high resolution X-ray gratings on board \emph{Chandra}. We found that ten of the fifteen AGN exhibit signatures of an intrinsic…
The mass loss properties of carbon AGB stars are not very well constrained at present. A variety of empirical or theoretical formulae with different parameterisations are available in the literature and the agreement between them is…
The origin of the so called 'detached shells' around AGB stars is not fully understood, but two common hypotheses state that these shells form either through the interaction of distinct wind phases or an eruptive mass loss associated with a…
We present the results from a study of the long-term optical spectral variations of BL Lacertae, using the long and well-sampled B and R-band light curves of the Whole Earth Blazar Telescope (WEBT) collaboration, binned on time intervals of…
New radio observations of the counterpart of the ultraluminous X-ray source in NGC 5408 show for the first time that the radio emission is resolved with an angular size of 1.5 to 2.0 arcseconds. This corresponds to a physical size of 35-46…
We propose that cosmological magnetic fields generated in regions of finite spatial dimensions may manifest themselves in the global dynamics of the Universe as `dark energy'. We test our model in the context of spatially flat cosmological…
The orientation of the local interstellar magnetic field introduces asymmetries in the heliosphere that affect the location of heliospheric radio emissions and the streaming direction of ions from the termination shock of the solar wind. We…
Reionization is thought to be dominated by low mass galaxies, while direct observations of resolved galaxies probe only the most massive, rarest objects. The cross-correlation between fluctuations in the surface brightness of the cumulative…
We determine the contribution of stars in galaxies, intracluster stars, and the intracluster medium to the total baryon budget in nearby galaxy clusters and groups. We find that the baryon mass fraction (f_b) within r500 is constant for…
We calculate the GeV spectra of GRB afterglows produced by inverse Compton scattering of the sub-MeV emission of these objects. We improve on earlier treatments by using refined afterglow parameters and new model developments motivated by…
Colliding winds of massive stars in binary systems are considered as candidate sites of high-energy non-thermal photon emission. They are already among the suggested counterparts for a few individual unidentified EGRET sources, but may…
Recycled dwarf galaxies can form in the collisional debris of massive galaxies. Theoretical models predict that, contrary to classical galaxies, they should be free of non-baryonic Dark Matter. Analyzing the observed gas kinematics of such…
We investigate the hydrodynamics of accretion channelled by a dipolar magnetic field (funnel flows). We consider situations in which the electrons and ions in the flow cannot maintain thermal equilibrium (two-temperature effects) due to…
We measure the first stellar velocity dispersion of the Leo A dwarf galaxy, \sigma = 9.3 +- 1.3 km/s. We derive the velocity dispersion from the radial velocities of ten young B supergiants and two HII regions in the central region of Leo…