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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)
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)
We report the discovery of a nearby, old, halo white dwarf candidate from the Sloan Digital Sky Survey. SDSS J110217.48+411315.4 has a proper motion of 1.75 ′′ /year and redder optical colors than all other known featureless (type DC) white dwarfs. We present SDSS imaging and spectroscopy of this object, along with near-infrared photometry obtained at the(More)
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)
We investigate the importance of the pseudo-continuum bound-free opacity from hydrogen atoms in the atmospheres of cool white dwarfs. This source of absorption, when calculated by the occupation probability formalism applied in the modeling of white dwarf atmospheres with T eff < 17000 K, dominates all other sources of opacity at optical wavelengths. This(More)
The adsorption of CO on the rutile TiO(2)(110) surface was investigated using He atom scattering (HAS), high resolution electron energy loss spectroscopy (HREELS), thermal desorption spectroscopy (TDS), and different types of ab initio electronic structure calculations. The experimental and theoretical results allow to put forward a consistent picture for(More)
The atmospheres of cool, helium-rich white dwarfs constitute an exotic and poorly explored physical regime of stellar atmospheres. Under physical conditions where the temperature varies from 1000K to 10000K, the density can reach values as large as 2 g/cm 3 , and the pressure is as high as 1 Mbar, the atmosphere is no longer an ideal gas and must be treated(More)
Uranium compounds α-Ba2[UO2(PO4)2] (1), β-Ba2[UO2(PO4)2] (2), and Ba2[UO2(AsO4)2] (3) were synthesized by H3BO3/B2O3 flux reactions, though boron is not incorporated into the structures. Phases 1 and 2 are topologically identical, but 1 is heavily distorted with respect to 2. An unusual UO7 pentagonal bipyramid occurs in 1, exhibiting a highly distorted(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 T eff < 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, near-and mid-infrared(More)