UVO 0825+15 is a hot bright helium-rich subdwarf which lies in K2 Field 5 and in a sample of intermediate helium-rich subdwarfs observed with Subaru/HDS. The K2 light curve shows low-amplitude variations, whilst the Subaru spectrum shows Pbiv absorption lines, indicative of a very high lead overabundance. UVO 0825+15 also has a high proper motion with kinematics typical for a thick disk star. Analyses of ultraviolet and intermediate dispersion optical spectra rule out a short-period binary companion, and provide fundamental atmospheric parameters of T eff = 38 900±270 K, log g/cm s −2 = 5.97 ± 0.11, log n He /n H = −0.57 ± 0.01, E B−V ≈ 0.03, and angular radius θ = 1.062±0.006×10−11 radians (formal errors). The high-resolution spectrum shows that carbon is > 2 dex subsolar, iron is approximately solar and all other elements heavier than argon are at least 2 -4 dex overabundant, including germanium, yttrium and lead. Approximately 150 lines in the blue-optical spectrum remain unidentified. The chemical structure of the photosphere is presumed to be determined by radiatively-dominated diffusion. The K2 light curve shows a dominant period around 10.8 h, with a variable amplitude, its first harmonic, and another period at 13.3 h. The preferred explanation is multi-periodic non-radial oscillation due to g-modes with very high radial order, although this presents difficulties for pulsation theory. Alternative explanations fail for lack of radial-velocity evidence. UVO 0825+15 represents the fourth member of a group of hot subdwarfs having helium-enriched photospheres and 3-4 dex overabundances of trans-iron elements, and is the first lead-rich subdwarf to show evidence of pulsations.

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The effect of oxygen loss on the luminescence of YBazCu307-, has been investigated by cathodoluminescence (CL) in the scanning electron microscope (SEM) and by Raman microprobe measurements. The results herein indicate that a CL band at 530 nm is related to oxygen loss rather than to impurity phases such as YZ03 formed in the material by electron irradiation in the SEM.

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The majority of hot subdwarf stars are low-mass core-helium-burning stars. Their atmospheres are generally helium deficient; however a minority have extremely heliumrich surfaces. An additional fraction have an intermediate surface-helium abundance, occasionally accompanied by peculiar abundances of other elements. We have identified a sample of 88 hot subdwarfs including 38 helium-deficient, 27 intermediate-helium and 23 extreme-helium stars for which radial-velocity and proper-motion measurements, together with distances, allow a calculation of Galactic space velocities. We have investigated the kinematics of these three groups to determine whether they belong to similar or different galactic populations. The majority of helium-deficient subdwarfs in our sample show a kinematic distribution similar to that of thick disk stars. Helium-rich sdBs show a more diverse kinematic distribution. Although the majority are probably disk stars, a minority show a much higher velocity dispersion consistent with membership of a Galactic halo population. Several of the halo subdwarfs are members of the class of "heavy-metal" subdwarfs discovered by Naslim et al. (2011, 2013).

In this work, the solid-phase crystallization kinetics of amorphous SiGe films deposited by low-pressure chemical-vapor deposition on oxidized Si wafers has been studied by x-ray diffraction, Raman spectroscopy, and ultraviolet reflectance. The microstructure of the fully crystallized films has also been analyzed using these techniques in combination with transmission electron microscopy. The Ge fraction of the films (x) was in the 0–0.38 interval. The samples were crystallized at temperatures ranging from 525 to 600 °C. The crystallization monitored by all techniques was found to follow the Avrami model. Different crystallization behaviors are distinguished depending on the Ge content of the films and the crystallization temperature. The results are discussed in terms of the identification of the nucleation site location and the dimensionality of the grain growth, taking into account the probe depth of the different techniques and the values of the Avrami exponent derived from the crystallization curves. The preferred orientations of the grains, the grain morphology, the lateral grain size, the presence of inter- and intragrain defects, the surface roughness, and the overall crystallinity of the fully crystallized films have also been studied and related to the observations concerning the crystallization process.