Using deep Hubble Space Telescope imaging, color-magnitude diagrams are constructed for the globular clusters 47 Tuc and NGC 6397. As expected, because of its lower metal abundance, the main sequence ...of NGC 6397 lies well to the blue of that of 47 Tuc. A comparison of the white dwarf cooling sequences of the two clusters, however, demonstrates that these sequences are indistinguishable over most of their loci - a consequence of the settling out of heavy elements in the dense white dwarf atmosphere and the near equality of their masses. Lower quality data on M4 continues this trend to a third cluster whose metallicity is intermediate between these two. While the path of the white dwarfs in the color-magnitude diagram is nearly identical in 47 Tuc and NGC 6397, the numbers of white dwarfs along the path are not. This results from the relatively rapid relaxation in NGC 6397 compared to 47 Tuc and provides a cautionary note that simply counting objects in star clusters in random locations as a method of testing stellar evolutionary theory is likely dangerous unless dynamical considerations are included.
The minute has given way to the second as an expression of radiographic exposure duration. It is predicted that the millisecond will be the term of the future. Arterial blood velocity exceeds 50 cm. ...per second. In cardiovascular radiography, especially angiocardiography, maximum detail cannot be achieved unless the x-ray exposure is short enough to "stop" rapid movement. Practical experience indicates that exposures of 3 milliseconds' duration offer an economic alternative to high speed, serial angiocardiography. A method of achieving such exposures consists of a grid-controlled, hightension, switch tube operated in series with the diagnostic x-ray tube.
An approach is introduced for incorporating the concept of stellar pollution into stellar evolution models. The approach involves enhancing the metal content of the surface layers of stellar models. ...In addition, the surface layers of stars in the mass range of 0.5-2.0 Solar masses are mixed to an artificial depth motivated by observations of lithium abundance. The behavior of polluted stellar evolution models is explored assuming the pollution occurs after the star has left the fully convective pre main sequence phase. Stellar models polluted with a few Earth masses of iron are significantly hotter than stars of the same mass with an equivalent bulk metallicity. Polluted stellar evolution models can successfully reproduce the metal-rich, parent star tau Bootis and suggest a slightly lower mass than standard evolution models. Finally, the possibility that stars in the Hyades open cluster have accreted an average of 0.5 Earth masses of iron is explored. The results indicate that it is not possible to rule out stellar pollution on this scale from the scatter of Hyades stars on a color-magnitude diagram. The small amount of scatter in the observational data set does rule out pollution on the order of 1.5 Earth masses of iron. Pollution effects at the low level of 0.5 Earth masses of iron do not produce substantial changes in a star's evolution.
The Hyades open cluster presents a unique laboratory for planet formation and stellar pollution studies because all of the stars have essentially the same age and were born from the same cloud of ...gas. Furthermore, with an age of roughly 650 Myr most of the intermediate and low mass stars are on the main sequence. Given these assumptions, the accretion of metal rich material onto the surface of a star during and shortly after the formation of planetary systems should be evident via the enhanced metallicity of the star. Building on previous work, stellar evolution models which include the effects of stellar pollution are applied to the Hyades. The results of several Monte Carlo simulations, in which the amount of accreted material is drawn at random from a Gaussian distribution with standard deviation equal to half the mean, are presented. An effective temperature-Fe/H relation is produced and compared to recent observations. The theoretical predictions presented in this letter will be useful in future searches for evidence of stellar pollution due to planet formation. It is concluded that stellar pollution effects at the mean level of >=2 Earth masses of iron are ruled out by current observational data.
We analyze extensive BVR_cI_c time-series photometry and radial-velocity measurements for WOCS 40007 (Auner 259; KIC 5113053), a double-lined detached eclipsing binary and a member of the open ...cluster NGC 6819. Utilizing photometric observations from the 1-meter telescope at Mount Laguna Observatory and spectra from the WIYN 3.5-meter telescope, we measure precise and accurate masses (~1.6% uncertainty) and radii (~0.5%) for the binary components. In addition, we discover a third star orbiting the binary with a period greater than 3000 days using radial velocities and Kepler eclipse timings. Because the stars in the eclipsing binary are near the cluster turnoff, they are evolving rapidly in size and are sensitive to age. With a metallicity of Fe/H=+0.09+/-0.03, we find the age of NGC 6819 to be about 2.4 Gyr from CMD isochrone fitting and 3.1+/-0.4 Gyr by analyzing the mass-radius (M-R) data for this binary. The M-R age is above previous determinations for this cluster, but consistent within 1 sigma uncertainties. When the M-R data for the primary star of the additional cluster binary WOCS 23009 is included, the weighted age estimate drops to 2.5+/-0.2 Gyr, with a systematic uncertainty of at least 0.2 Gyr. The age difference between our CMD and M-R findings may be the result of systematic error in the metallicity or helium abundance used in models, or due to slight radius inflation of one or both stars in the WOCS 40007 binary.
It is noted that universal grammars & typological studies apply the notion of adposition designating a lexical category of concrete (local, temporal, modal) & abstract (grammatical) relations as a ...parameter in the classification of langs. A sample of 31 langs selected from J. A. Hawkins's study (Word Order Universals, Quantitative Analysis of Linguistic Structure 3, New York, 1983) was analyzed to test the hypothesis that the correlation between adposition & genitive serialization is high because langs that have no genitive construction code the genitive adpositionally. Results contradicted this hypothesis; a direct relationship between adposition & genitive was attested very rarely. 50 References. Z. Dubiel
We substantially update the capabilities of the open source software package Modules for Experiments in Stellar Astrophysics (MESA), and its one-dimensional stellar evolution module, MESA Star. ...Improvements in MESA Star's ability to model the evolution of giant planets now extends its applicability down to masses as low as one-tenth that of Jupiter. The dramatic improvement in asteroseismology enabled by the space-based Kepler and CoRoT missions motivates our full coupling of the ADIPLS adiabatic pulsation code with MESA Star. This also motivates a numerical recasting of the Ledoux criterion that is more easily implemented when many nuclei are present at non-negligible abundances. This impacts the way in which MESA Star calculates semi-convective and thermohaline mixing. We exhibit the evolution of 3-8 Msun stars through the end of core He burning, the onset of He thermal pulses, and arrival on the white dwarf cooling sequence. We implement diffusion of angular momentum and chemical abundances that enable calculations of rotating-star models, which we compare thoroughly with earlier work. We introduce a new treatment of radiation-dominated envelopes that allows the uninterrupted evolution of massive stars to core collapse. This enables the generation of new sets of supernovae, long gamma-ray burst, and pair-instability progenitor models. We substantially modify the way in which MESA Star solves the fully coupled stellar structure and composition equations, and we show how this has improved MESA's performance scaling on multi-core processors. Updates to the modules for equation of state, opacity, nuclear reaction rates, and atmospheric boundary conditions are also provided. We describe the MESA Software Development Kit (SDK) that packages all the required components needed to form a unified and maintained build environment for MESA. Abridged
Two cases of bleeding from gastroesophageal varices treated by variceal obliteration illustrate multiple routes of variceal supply, and alert embolizing angiographers to the presence of spontaneous ...portosystemic shunts which should be kept open. In one case, variceal obliteration required embolization of the left gastric vein and a transhepatic collateral originating from the left hepatic portal branch and contributing substantially to variceal filling. A second patient with a relatively large spontaneous splenorenal shunt had recurrent variceal bleeding two months after a successful embolization of the coronary vein and a short gastric vein. A repeat study revealed the recurrent varices were supplied by enlarged right gastric and gastroepiploic veins. Superior mesenteric venography was necessary for their visualization.
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