Circumstellar interaction of the type Ia supernova 2002ic

We propose a model to account for the bolometric light curve, quasi-continuum and the Ca II emission features of the peculiar type Ia supernova (SN) 2002ic, which exploded in a dense circumstellar envelope. The model suggests that the SN Ia had the maximum possible kinetic energy and that the ejecta expand in an approximately spherically symmetric (possibly clumpy) circumstellar environment. The Ca II and quasi-continuum are emitted by shocked SN ejecta that underwent deformation and fragmentation in the intershock layer. Modeling of the Ca II triplet implies that the contribution of the O I 8446 A line is about 25% of the 8500 A feature on day 234, which permits us to recover the flux in the Ca II 8579 A triplet from the flux of 8500 A blend reported by Deng et al. (2004). We use the Ca II doublet and triplet fluxes on day 234 to derive the electron temperature (~4400 K) in the Ca II line-emitting zone and the ratio of the total area of dense fragments to the area of the shell, S/S_0 ~ 100. We argue that Ca II bands and quasi-continuum originate from different zones of the shocked ejecta that reflect the abundance stratification of the supernova.Comment: 12 pages, MNRAS, in pres

Flow-Driven Cloud Formation and Fragmentation: Results From Eulerian and Lagrangian Simulations

The fragmentation of shocked flows in a thermally bistable medium provides a natural mechanism to form turbulent cold clouds as precursors to molecular clouds. Yet because of the large density and temperature differences and the range of dynamical scales involved, following this process with numerical simulations is challenging. We compare two-dimensional simulations of flow-driven cloud formation without self-gravity, using the Lagrangian Smoothed Particle Hydrodynamics (SPH) code VINE and the Eulerian grid code Proteus. Results are qualitatively similar for both methods, yet the variable spatial resolution of the SPH method leads to smaller fragments and thinner filaments, rendering the overall morphologies different. Thermal and hydro-dynamical instabilities lead to rapid cooling and fragmentation into cold clumps with temperatures below 300K. For clumps more massive than 1 Msun/pc, the clump mass function has an average slope of -0.8. The internal velocity dispersion of the clumps is nearly an order of magnitude smaller than their relative motion, rendering it subsonic with respect to the internal sound speed of the clumps, but supersonic as seen by an external observer. For the SPH simulations most of the cold gas resides at temperatures below 100K, while the grid-based models show an additional, substantial component between 100 and 300K. Independently of the numerical method our models confirm that converging flows of warm neutral gas fragment rapidly and form high-density, low-temperature clumps as possible seeds for star formation.Comment: 9 pages, 8 figures, MNRAS accepte

Supersonic turbulence in shock-bound interaction zones I: symmetric settings

Colliding hypersonic flows play a decisive role in many astrophysical objects. In this paper, we look at the idealized model of a 2D plane parallel isothermal slab (CDL) and at symmetric settings, where both flows have equal parameters. We performed a set of high-resolution simulations with upwind Mach numbers, 5 < M_u < 90. We find that the CDL is irregularly shaped and has a patchy and filamentary interior. The size of these structures increases with l_cdl, the extension of the CDL. On average, but not at each moment, the solution is about self-similar and depends only on M_u. We find the root mean square Mach number to scale as M_rms ~ 0.2 M_u. Independent of M_u is the mean density, rho_m ~ 30 rho_u. The fraction f_eff of the upwind kinetic energy that survives shock passage scales as f_eff= 1 - M_rms^(-0.6). This dependence persists if the upwind flow parameters differ from one side to the other of the CDL, indicating that the turbulence within the CDL and its driving are mutually coupled. In the same direction points the finding that the auto-correlation length of the confining shocks and the characteristic length scale of the turbulence within the CDL are proportional. In summary, larger upstream Mach numbers lead to a faster expanding CDL with more strongly inclined confining interfaces relative to the upstream flows, more efficient driving, and finer interior structure relative to the extension of the CDL.Comment: version sent to publisher, final language/typo corrections made. 23 pages, 19 figures, accepted for publication in A&A, version with high quality color images can be found at http://www.astro.phys.ethz.ch/papers/folini/folini_p_nf.htm

Radiometric monitoring of atmospheric water vapor as it pertains to phase correction in millimeter interferometry

Water vapor in the Earth's troposphere produces fluctuations in the phase of millimeter-wavelength radiation from astronomical sources. Such fluctuations seriously limit the spatial resolution achievable with current millimeter interferometers. Since water vapor is also a source of atmospheric opacity at these wavelengths, radiometric measurements of sky brightness may be used to monitor the fluctuating water vapor content of the atmosphere and thereby the fluctuations in the interferometric phase. The atmospheric opacity depends on the frequency and on the physical conditions of those atmospheric regions in which the water vapor is located. Atmospheric temperature influences the strengths of the various absorption lines, and pressure influences the degree of line broadening. The magnitude of the phase fluctuations relative to the brightness fluctuations is therefore also dependent on frequency, temperature, and pressure. The frequency of a radiometric monitoring system may be chosen to minimize the dependence of this ratio on the atmospheric parameters.


Human adipocyte glucose transport system. Biochemical and functional heterogeneity of hexose carriers.

We have investigated glucose transport proteins in isolated human adipocytes. Using the cytochalasin B binding assay to measure glucose transporters in subcellular membrane subfractions, we found that insulin induced translocation of intracellular glucose transporters to the cell surface. Isoelectric focusing of glucose transporters photolabeled with [3H]cytochalasin B revealed two distinct glucose transporter isoforms in low density microsomes focusing at pH 5.6 and pH 6.4, but only the pH 5.6 isoform was detectable in plasma membranes and only the pH 6.4 form was found in the high density microsomes. Insulin recruited only the pH 5.6 glucose transporter from the low density microsomes to the plasma membrane with no effect on the pH 6.4 transporter isoform. The results suggest that the pH 6.4 species is an immature form of the glucose transporter initially located in the high-density microsome fraction, which then migrates to the low-density microsomes where it matures (converted to pH 5.6 species) and becomes available for insulin-mediated recruitment to the plasma membrane

Reduced reshock growth in a convergent/divergent system: Effect of reshock strength

The Richtmyer-Meshkov instability creates or seeds hydrodynamic instabilities that will mix cold shell material into the hot DT fuel in an ignition capsule and may prevent ignition. Characteristic of this process is multiple shocks crossing converging interfaces. To mimic this situation, strong converging shocks were created, passed over an unstable interface, reflected by an inner cylinder, and then reshocked the interface. Analysis of the mix width at the unstable surface shows no additional growth, within experimental uncertainty, due to an initially perturbed surface and no dependence on reshock strength