The electron temperature of the inner halo of the Planetary Nebula NGC 6543

We investigate the electron temperature of the inner halo and nebular core regions of NGC 6543, using archival Hubble Space Telescope (HST) Wide Field Planetary Camera 2 (WFPC2) images taken through narrow band [O III] filters. Balick et al. (2001) showed that the inner halo consists of a number of spherical shells. We find the temperature of this inner halo to be much higher (~15000 K) than that of the bright core nebula (~8500 K). Photo-ionization models indicate that hardening of the UV radiation from the central star cannot be the main source of the higher temperature in the halo region. Using a radiation hydrodynamic simulation, we show that mass loss and velocity variations in the AGB wind can explain the observed shells, as well as the higher electron temperature.Comment: 9 pages, 6 figures, to be published in A&

Detection of Fluorine in the Halo Planetary Nebula BoBn 1: Evidence For a Binary Progenitor Star

We have found the fluorine lines [F IV] 3996.92A,4059.90A in the extremely metal-poor ([Ar/H] = -2.10+/-0.21) halo planetary nebula (PN) BoBn 1 in high-dispersion spectra from the 8.2-m VLT/UVES archive. Chemical abundance analysis shows that the fluorine abundance is [F/H] = +1.06+/-0.08, making BoBn 1 the most fluorine-enhanced and metal-poor PN among fluorine-detected PNe and providing new evidence that fluorine is enhanced by nucleosynthesis in low mass metal-poor stars. A comparison with the abundances of carbon-enhanced metal-poor (CEMP) stars suggests that BoBn 1 shares their origin and evolution with CEMP-s stars such as HE1305+0132. BoBn 1 might have evolved from a binary consisting of ~2 Msun primary and ~0.8 Msun secondary stars.Comment: 13 pages, 3 figures, accepted by ApJ Letter

SIMULATIONS of VISCOUS ACCRETION FLOW AROUND BLACK HOLES in A TWO-DIMENSIONAL CYLINDRICAL GEOMETRY

We simulate shock-free and shocked viscous accretion flows onto a black hole in a two-dimensional cylindrical geometry, where initial conditions were chosen from analytical solutions. The simulation code used the Lagrangian total variation diminishing plus remap routine, which enabled us to attain high accuracy in capturing shocks and to handle the angular momentum distribution correctly. The inviscid shock-free accretion disk solution produced a thick disk structure, while the viscous shock-free solution attained a Bondi-like structure, but in either case, no jet activity nor any quasi-periodic oscillation (QPO)-like activity developed. The steady-state shocked solution in the inviscid as well as in the viscous regime matched theoretical predictions well. However, increasing viscosity renders the accretion shock unstable. Large-amplitude shock oscillation is accompanied by intermittent, transient inner multiple shocks. This oscillation of the inner part of the disk is interpreted as the source of QPO in hard X-rays observed in micro-quasars. Strong shock oscillation induces strong episodic jet emission. The jets also show the existence of shocks, which are produced as one shell hits the preceding one. The periodicities of the jets and shock oscillation are similar; the jets for the higher viscosity parameter appear to be stronger and faster.clos