Piotr M. Kowalski

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We report the vibrational properties of H(4)SiO(4), D(4)SiO(4), H(6)Si(2)O(7), and H(6)Si(3)O(9) in aqueous solution at 300 K and 1000 K, obtained from the combination of ab initio molecular dynamics (MD) and a mode-decomposition approach. This combination yields vibrational subspectra for selected vibrational modes at finite temperatures. We also performed(More)
The dynamics of an F center created by an oxygen vacancy on the TiO₂(110) rutile surface has been investigated using ab initio molecular dynamics. These simulations uncover a truly complex, time-dependent behavior of fluctuating electron localization topologies in the vicinity of the oxygen vacancy. Although the two excess electrons are found to populate(More)
We investigate the importance of the far red wing of the Lyman α line of hydrogen in the atmospheres of cool white dwarfs of pure hydrogen composition. We find that this absorption process dominates all important sources of opacity in the blue part of the optical spectrum of these stars. Our successful fits to the spectra of cool DA/DC white dwarfs indicate(More)
Isotopic and trace element variations within single diamond crystals are widely known from both natural stones and synthetic crystals. A number of processes can produce variations in carbon isotope composition and nitrogen abundance in the course of diamond crystallization. Here, we present evidence of carbon and nitrogen fractionation related to the(More)
We investigate the ionization and the opacity of warm, dense helium under conditions found in the atmospheres of cool white dwarf stars. Our particular interest is in densities up to 3 g/cm3 and temperatures from 1000K to 10000K. For these physical conditions various approaches for modeling the ionization equilibrium predict ionization fractions that differ(More)
We present Spitzer 5-15 μm spectroscopy of one cool white dwarf and 3.6 – 8 μm photometry of 51 cool white dwarfs with Teff < 6000 K. The majority of our targets have accurate BVRIJHK photometry and trigonometric parallax measurements available, which enables us to perform a detailed model atmosphere analysis using their optical, nearand mid-infrared(More)
Aims. We discuss the importance of pure hydrogen white dwarf atmosphere models with Ly-α far red wing opacity in the analysis of the white dwarf cooling sequence of the globular cluster NGC 6397. Methods. Our recently improved atmosphere models account for the previously missing opacity from the Ly-α hydrogen line broadened by collisions of the absorbing(More)
There are several ways planets can survive the giant phase of the host star, hence one can consider the case of Earth-like planets orbiting white dwarfs. As a white dwarf cools from 6000K to 4000K, a planet orbiting at 0.01 AU from the star would remain in the continuous habitable zone (CHZ) for about 8Gyr. Polarisation due to a terrestrial planet in the(More)
We consider the problem of radiative transfer in stellar atmospheres where the index of refraction departs from unity and is a function of density and temperature. We present modified Feautrier and Lambda-iteration methods to solve the equation of radiative transfer with refraction in a plane parallel atmosphere. These methods are general and can be used in(More)