Abundance studies of sdB stars using UV echelle HST/STIS spectroscopy

Aims: We test the hypothesis that the pulsations in sdB stars are correlated with the surface abundances of iron-group elements. Any correlation might explain why, when given two spectroscopically similar stars, one will pulsate while the other will not. Methods: We have obtained high-resolution ultraviolet spectra two pulsating and three non-pulsating sdB stars using the Space Telescope Imaging Spectrograph onboard the Hubble Space Telescope. We determined abundances for 25 elements including the iron group and even heavier elements such as tin and lead using LTE curve-of-growth and spectrum synthesis techniques. Results: We find no clear correlation between pulsations and metal abundances, and we comment on the resulting implications, including whether it is possible to determine the difference between a pulsating and a non-pulsating sdB spectroscopically. In addition to the main goal of our observations, we have also investigated the effect of supersolar metallicity on fundamental parameter determination, possible trends with iron abundance, and the hypothesis that weak winds may be selectively removing elements from the stellar envelopes. These effects provide challenges to stellar atmosphere modelling and diffusion models for sdB stars.Comment: 14 pages, 12 figures, accepted for publication in A&

Discovery of magnetic fields in hot subdwarfs

We present initial results of a project to measure mean longitudinal magnetic fields in a group of sdB/OB/O stars. The project was inspired by the discovery of three super-metal-rich sdOB stars, each having metals (e.g. Ti, V) enhanced by factors of 10^3 to 10^5. Similar behaviour is observed in chemically peculiar A stars, where strong magnetic fields are responsible for the enrichment. With this in mind, we obtained circularly polarised spectra of two of the super-metal-rich sdOBs, two "normal" sdBs and two sdOs using FORS1 on the ESO/VLT. By examining circular polarisation in the hydrogen Balmer lines and in helium lines, we have detected magnetic fields with strengths of 1-2 kG in most of our targets. This suggests that such fields are relatively common in hot subdwarfs.Comment: 4 pages, to appear in White Dwarfs, eds. D. Koester, S. Moehler, ASP Conf. serie

Time resolved spectroscopy of the multiperiodic pulsating subdwarf B star PG1605+072

We present results for the 2m spectroscopic part of the MultiSite Spectroscopic Telescope campaign, which took place in May/June 2002. In order to perform an asteroseismological analysis on the multiperiodic pulsating subdwarf B star PG 1605+072 we used over 150 hours of time resolved spectroscopy in order to search for and analyse line profile variations by using phase binning. We succeeded in finding variations in effective temperature and gravity for four modes. A pilot analysis using the \textit{BRUCE} and \textit{KYLIE} programs and assuming strong rotation and low inclination favours models with $l=1$ or $l=2$ with $m\leq0$.Comment: 2 pages, 2 figures, proceedings of the "Vienna Workshop on the Future of Asteroseismology", to appear in Communications in Asteroseismology v. 14

Epitaxial undoped indium oxide thin films: Structural and physical properties.

Indium oxide thin films were grown by the pulsed electron beam deposition method on c-cut sapphire substrates at 10−2 mbar oxygen pressure and temperature up to 500 1C. Such conditions lead to the formation of dense, smooth and stoichiometric In2O3 films, with the cubic bixbyite structure. Epitaxial thin films were obtained at substrate temperatures as low as 200 1C. Pole figure measurements indicate the existence of (111) oriented In2O3 crystallites with different in-plane symmetry, i.e. three-fold and six-fold symmetry. The origin of this effect may be related to the specificities of the growth method which can induce a large disorder in the oxygen network of In2O3, leading then to a six-fold symmetry in the (111) plane of the bixbyite structure. This temperature resistivity behaviour shows metallic conductivity at room temperature and a metal– semiconductor transition at low temperature for In2O3 films grown at 200 1C, while the classical semiconductor behaviour was observed for the films grown at 400 and 500 1C. A maximum mobility of 24.7 cm2/V s was measured at 200 1C, and then it falls off with improving the crystalline quality of films. The optical transparency is high (480%) in a spectral range from 500 nm to 900 nm

Performance and Evaluation of Swine House Heating with a Solar Energy Intensifier-thermal Energy Storage System

The urgency for energy independence in the United States is unprecedented in its history. The demand for energy is reflected in rising fuel costs which affects every segment of the economy. Among the most severely affected sectors is the agriculture industry, whose fossil fuel consumption is crucial to its efficient production of food and fiber. Solar, one of several alternative energy sources being developed nationwide has unique possibilities in the U.S. agriculture system. Large areas are available for locating collector units, and the energy requirements in the farm are low compared with the available radiation falling on the area. Drying of harvested crops and space heating of farm buildings can efficiently utilize low quality heat which can be generated with simple, inexpensive, solar equipment. Consequently, the agriculture industry has excellent opportunities to develop widespread application of solar energy systems. At least three serious problems exist in the development of a successful agricultural solar system. First, the seasonal variability of solar radiation, in the Great Plains region, is such that when the demand for energy on the farm peaks during the fall and winter, the amount of available radiation is at its lowest level. Second, thermal energy collection ceases during nighttime hours when the coldest temperatures occur. The third problem is the design and construction of an economical and reliable system that can be used for more than one application to increase its annual utilization. A contractor system can be used to intensify low level solar radiation onto a small collector and thereby achieve the required temperature range for agricultural applications. A thermal energy storage unit can be used to allow nighttime delivery of energy collected during the day. Finally, by producing air temperatures that are compatible with both grain drying and preheating of ventilation air, a single system can be utilized for a greater number of days during the year. A solar energy intensifier-thermal energy storage (SEI-TES) system was designed to incorporate all three of the aspects and to enhance the feasibility of solar energy for agriculture use. A unique location for the thermal energy storage unit in the system was included in the design to reduce heat losses and improve performance. To investigate the feasibility of the multiple-use SEI-TES system, research was conducted with the following objectives: 1. Test the SEI-TES for preheating swine house ventilation air under actual operating conditions. 2. Evaluate the performance and operating characteristics of the SEI-TES system

D'atri spaces of type k and related classes of geometries concerning jacobi operators

In this article we continue the study of the geometry of $k$-D'Atri spaces, $$ $\leq n-1$ ($n$ denotes the dimension of the manifold)$,$ began by the second author. It is known that $k$-D'Atri spaces, $k\geq 1,$ are related to properties of Jacobi operators $R_{v}$ along geodesics, since she has shown that ${\operatorname{tr}}R_{v}$, ${\operatorname{tr}}R_{v}^{2}$ are invariant under the geodesic flow for any unit tangent vector $v$. Here, assuming that the Riemannian manifold is a D'Atri space, we prove in our main result that ${\operatorname{tr}}R_{v}^{3}$ is also invariant under the geodesic flow if $k\geq 3$. In addition, other properties of Jacobi operators related to the Ledger conditions are obtained and they are used to give applications to Iwasawa type spaces. In the class of D'Atri spaces of Iwasawa type, we show two different characterizations of the symmetric spaces of noncompact type: they are exactly the $\frak{C}$-spaces and on the other hand they are $k$ -D'Atri spaces for some $k\geq 3.$ In the last case, they are $k$-D'Atri for all $k=1,...,n-1$ as well. In particular, Damek-Ricci spaces that are $k$-D'Atri for some $k\geq 3$ are symmetric. Finally, we characterize $k$-D'Atri spaces for all $k=1,...,n-1$ as the $\frak{SC}$-spaces (geodesic symmetries preserve the principal curvatures of small geodesic spheres). Moreover, applying this result in the case of 4% -dimensional homogeneous spaces we prove that the properties of being a D'Atri (1-D'Atri) space, or a 3-D'Atri space, are equivalent to the property of being a $k$-D'Atri space for all $k=1,2,3$.Comment: 19 pages. This paper substitute the previous one where one Theorem has been deleted and one section has been adde

Sites of synthesis and transport of photosynthetic products within the leaf cell

Abstract1.1. After illumination of leaves in the presence of 14CO2 for various times and subsequent freeze drying, chloroplasts were isolated using a nonaqueous procedure. The time-course of the distribution of a number of compounds between chloroplasts and the remainder of the cell was calculated from the 14C-incorporation into the fractions obtained.2.2. Labelled ribulose diphosphate, sedoheptulose diphosphate and sedoheptulose monophosphate occurred, at least during the first minutes of photosynthesis, solely in the chloroplasts. At the beginning of photosynthesis phosphoglyceric acid, fructose diphosphate, fructose monophosphate and glucose monophosphate appeared first in the chloroplasts, but were found later also in the non-chloroplastic part of the cell. The major part of glucose diphosphate, uridine diphosphoglucose, sucrose, malic acid and citric acid was always located in the non-chloroplastic part of the cell.3.3. From the results it is concluded that the photosynthetic carbon cycle operates exclusively in the chloroplasts. Sugar phosphates, which are not needed in the cyclic regeneration of the CO2-acceptor, are directly translocated into the cytoplasm. The synthesis of uridine diphosphoglucose takes place mainly in the cytoplasm. Glucose diphosphate and possibly also sucrose seem to be formed in the cytoplasm of the leaf cell

The subdwarf B star SB 290 - A fast rotator on the extreme horizontal branch

Hot subdwarf B stars (sdBs) are evolved core helium-burning stars with very thin hydrogen envelopes. In order to form an sdB, the progenitor has to lose almost all of its hydrogen envelope right at the tip of the red giant branch. In close binary systems, mass transfer to the companion provides the extraordinary mass loss required for their formation. However, apparently single sdBs exist as well and their formation is unclear since decades. The merger of helium white dwarfs leading to an ignition of core helium-burning or the merger of a helium core and a low mass star during the common envelope phase have been proposed. Here we report the discovery of SB 290 as the first apparently single fast rotating sdB star located on the extreme horizontal branch indicating that those stars may form from mergers.Comment: 5 pages, 4 figures, A&A letters, accepte

Internal rotation of subdwarf B stars: limiting cases and asteroseismological consequences

Observations of the rotation rates of horizontal branch (HB) stars show puzzling systematics. In particular, cooler HB stars often show rapid rotation (with velocities in excess of 10 km/s), while hotter HB stars typically show much smaller rotation velocities. Simple models of angular momentum evolution of stars from the main sequence through the red giant branch fail to explain these effects. In general, evolutionary models in all cases preserve a rapidly rotating core. The observed angular velocities of HB stars require that some of the angular momentum stored in the core reaches the surface. To test the idea that HB stars contain such a core, one can appeal to detailed computations of trace element abundences and rotational mixing. However, a more direct probe is available to test these limiting cases of angular momentum evolution. Some of the hottest horizontal branch stars are members of the pulsating sdB class. They frequently show rich pulsation spectra characteristic of nonradially pulsating stars. Thus their pulsations probe the internal rotation of these stars, and should show the effects of rapid rotation in their cores. Using models of sdB stars that include angular momentum evolution, we explore this possibility and show that some of the sdB pulsators may indeed have rapidly rotating cores.Comment: accepted for publication in The Astrophysical Journa