We derive a new perturbative quantum master equation for the reduced density matrix of a system interacting with an environment (with a dense spectrum of energy levels). The total system energy (system plus environment) is constant and finite. This equation takes into account the finite energy effects of the environment due to the total energy

Stellar clusters with the same general physical properties (e.g., total mass, age, and star-formation mode) may have very different stellar mass spectra due to the incomplete sampling of the underlying mass function; such differences are especially relevant in the high-mass tail of the mass function due to the smaller absolute number of massive

The numerical simulation method for variable white dwarfs of Ising & Koester (2001) is extended to variable DB stars (DBVs or V777 Herculis stars). We find the same general behavior of nonlinear effects, with a sinusoidal light-curve at small amplitudes, strongly non-sinusoidal variations at intermediate amplitudes and a change back to smaller and

We present evidence of the coexistence of either an AGN or an ultraluminous X-ray source, together with a young superstellar cluster, in the central 3 pc of NGC 4303. The galaxy contains a low-luminosity AGN and hosts a number of starburst regions in a circumnuclear spiral, as well as in the nucleus itself. A high spatial resolution Chandra image

With the goal of producing a reliable set of model atoms and singly ionized ions for use in building NLTE model atmospheres, we have combined measured energy levels, critically compiled line transition probabilities, and resonance-averaged calculations of photoionization cross sections. A majority of the elements from Li to Ca are considered

A lightcurve of comet 6P/d'Arrest from R-band CCD images taken at La Palma 2.52 m NOT telescope is presented. The lightcurve shows noticeable periodic changes in brightness produced by rotational modulation. The periodogram analysis of the lightcurve shows a peak with a confidence level exceeding 99.9% at 3.336 h. Assuming an elongated nucleus, the