WR 118 is a highly evolved Wolf-Rayet star of the WC10 subtype surrounded by a permanent dust shell absorbing and re-emitting in the infrared a considerable fraction of the stellar luminosity. We ...present the first diffraction-limited 2.13 μm speckle interferometric observations of WR 118 with 73 mas resolution. The speckle interferograms were obtained with the 6 m telescope at the Special Astrophysical Observatory. The two-dimensional visibility function of the object does not show any significant deviation from circular symmetry. The visibility curve declines towards the diffraction cut-off frequency to ~0.66 and can be approximated by a linear function. Radiative transfer calculations have been carried out to model the spectral energy distribution, given in the range of 0.5-25 μm, and our 2.13 μm visibility function, assuming spherical symmetry of the dust shell. Both can be fitted with a model containing double-sized grains ("small" and "large" ) with the radii of $a = 0.05$ μm and 0.38 μm, and a mass fraction of the large grains greater than 65% . Alternatively, a good match can be obtained with the grain size distribution function $n(a) \sim a^{-3}$, with a ranging between 0.005 μm and 0.6 μm. At the inner boundary of the modelled dust shell (angular diameter $\Theta_{\rm in} = (17 \pm 1)$ mas), the temperature of the smallest grains and the dust shell density are 1750 K ± 100 K and $(1 \pm 0.2) \times 10^{-19}$ g/cm3, respectively. The dust formation rate is found to be $(1.3 \pm 0.5) \times 10^{-7}$ $M_{\odot}$/yr, assuming $V_{\rm wind} = 1200$ km s-1.
The evolution on the AGB and beyond is reviewed with respect to the origin of Wolf-Rayet central stars. We focus on thermal pulses due to their particular importance for the evolution of hydrogen ...deficient stars. It is shown that overshoot applied to all convection regions is a key ingredient to model these objects leading to intershell abundances already close to the surface abundances of Wolf-Rayetcentral stars. In contrast to standard evolutionary calculations, overshoot models do show dredge up for very low envelope masses and efficient dredge up was found even during the post-AGB stage. Three thermal pulse scenarios for Wolf-Rayet central stars can nowbe distinguished: an AGB Final Thermal Pulse (AFTP) occurring at the very end of the AGB evolution, a Late Thermal Pulse (LTP) occurring during the post-AGBevolution when hydrogen burning is still on, and a Very Late Thermal Pulse (VLTP) occurring on the cooling branch when hydrogen burning has already ceased. All scenarios lead to hydrogen-deficient post-AGB stars with carbon and oxygen abundances as observed for Wolf-Rayet stars.Hydrogen is either diluted by dredge up (AFTP, LTP) or completely burnt (VLTP).
Nonideal effects of interacting charged particles are described by Padé approximants. The corresponding excess pressure is valid at any electron degeneracy and Coulomb coupling, and is applicable to ...arbitrary chemical mixtures. We give comparisons with various model calculations for the equation of state, and present results for pure and mixed H, He, and O plasmas.
This research analyzes gender differences in concern toward general and local environmental issues. Findings from a local survey indicate that women are no more concerned than are men about general ...environmental issues, but are significantly more concerned about the local environmental issues. Those participating in the labor force are more environmentally concerned than are nonparticipants. While mothers of small children in our sample show less concern over the effects on the economy of implementing environmental controls, fathers are more concerned about these effects.
We present the first speckle interferometric observations of R CrB, the prototype of a class of peculiar stars which undergo irregular declines in their visible light curves. The observations were ...carried out with the 6 m telescope at the Special Astrophysical Observatory near maximum light ($V=7$, 1996 Oct. 1) and at minimum light ($V=10.61$, 1999 Sep. 28). A spatial resolution of 75 mas was achieved in the K-band. The dust shell around R CrB is partially resolved, and the visibility is approximately 0.8 at a spatial frequency of 10 cycles/arcsec. The two-dimensional power spectra obtained at both epochs do not show any significant deviation from circular symmetry. The visibility function and spectral energy distribution obtained near maximum light can be simultaneously fitted with a model consisting of the central star and an optically thin dust shell with density proportional to r-2. The inner boundary of the shell is found to be 82 $R_{\star}$ (19 mas) with a temperature of 920 K. However, this simple model fails to simultaneously reproduce the visibility and spectral energy distribution obtained at minimum light. We show that this discrepancy can be attributed to thermal emission from a newly formed dust cloud.
An adult female neutered crossbred dog was referred in respiratory distress. Thoracic radiographs revealed tracheal narrowing‐with a soft tissue opacity dorsal to the trachea, near the thoracic ...inlet, and a patchy interstitial pulmonary infiltrate. The tracheal narrowing was thought to be due to a combination of intraluminal haemorrhage and mediastinal haemorrhage resulting from a coagulopathy caused by anticoagulant rodenticide intoxication. Treatment included supportive care and administration of vitamin K1, and the dog showed a complete resolution of the clinical signs.
PDF
