Planetary nebulae in M33: probes of AGB nucleosynthesis and ISM abundances

We have obtained deep optical spectrophotometry of 16 planetary nebulae in M33, mostly located in the central two kpc of the galaxy, with the Subaru and Keck telescopes. We have derived electron temperatures and chemical abundances from the detection of the [OIII]4363 line for the whole sample. We have found one object with an extreme nitrogen abundance, 12+log(N/H)=9.20, accompanied by a large helium content. After combining our data with those available in the literature for PNe and HII regions, we have examined the behavior of nitrogen, neon, oxygen and argon in relation to each other, and as a function of galactocentric distance. We confirm the good correlation between Ne/H and O/H for PNe in M33. Ar/H is also found to correlate with O/H. This strengthens the idea that at the metallicity of the bright PNe analyzed in M33, which is similar to that found in the LMC, these elements have not been significantly modified during the dredge-up processes that take place during the AGB phase of their progenitor stars. We find no significant oxygen abundance offset between PNe and HII regions at any given galactocentric distance, despite the fact that these objects represent different age groups in the evolution of the galaxy. Combining the results from PNe and HII regions, we obtain a representative slope of the ISM alpha-element (O, Ar, Ne) abundance gradient in M33 of -0.025 +/- 0.006 dex/kpc. Both PNe and HII regions display a large abundance dispersion at any given distance from the galactic center. We find that the N/O ratio in PNe is enhanced, relative to the HII regions, by approximately 0.8 dex.Comment: 21 pages, 20 figures. Accepted for publication in MNRA

The fractal dimension of star-forming regions at different spatial scales in M33

We study the distribution of stars, HII regions, molecular gas, and individual giant molecular clouds in M33 over a wide range of spatial scales. The clustering strength of these components is systematically estimated through the fractal dimension. We find scale-free behavior at small spatial scales and a transition to a larger correlation dimension (consistent with a nearly uniform distribution) at larger scales. The transition region lies in the range 500-1000 pc. This transition defines a characteristic size that separates the regime of small-scale turbulent motion from that of large-scale galactic dynamics. At small spatial scales, bright young stars and molecular gas are distributed with nearly the same three-dimensional fractal dimension (Df <= 1.9), whereas fainter stars and HII regions exhibit higher values (Df = 2.2-2.5). Our results indicate that the interstellar medium in M33 is on average more fragmented and irregular than in the Milky Way.Comment: 18 pages including 4 figures. Accepted for publication in Ap

Formal change impact analyses for emulated control software

Processor emulators are a software tool for allowing legacy computer programs to be executed on a modern processor. In the past emulators have been used in trivial applications such as maintenance of video games. Now, however, processor emulation is being applied to safety-critical control systems, including military avionics. These applications demand utmost guarantees of correctness, but no verification techniques exist for proving that an emulated system preserves the original system’s functional and timing properties. Here we show how this can be done by combining concepts previously used for reasoning about real-time program compilation, coupled with an understanding of the new and old software architectures. In particular, we show how both the old and new systems can be given a common semantics, thus allowing their behaviours to be compared directly

Mirror Neutrinos and the Early Universe

I review the construction of the Exact Parity or Mirror Matter Model and explain how it solves the solar and atmospheric neutrino problems. The oscillation driven relic neutrino asymmetry amplification phenomenon is then used to demonstrate the consistency of the model with Big Bang Nucleosynthesis.Comment: 7 pages, 2 embedded figures, Latex, uses ws-p8-50x6-00. Invited talk at COSMO99, to appear in the proceeding

New Regime for Dense String Networks

We uncover a new transient regime that reconciles the apparent inconsistency of the Martins Shellard one scale damped string evolution model with the initial conditions predicted by the Kibble mechanism for string formation in a second order phase transition. This regime carries (in a short cosmic time $\sim .1 t_c$) the dense string network created by the Kibble {\it{mechanism}} to the (dilute) Kibble {\it{regime}} in which friction dominated strings remain till times $t_* \sim (M_P/T_c)^2 t_c$. This is possible beacause the cosmic time at the phase transition ($t_c$) is much larger than the damping time scale $l_f\sim T_c^2/T^3$. Our result has drastic implications for various non-GUT scale string mediated mechanisms.}Comment: Talk presented at COSMO99, Trieste, Sept. 26- Oct. 2, 1999. Based on work done in collaboration with Michiyasu Nagasawa and Vikram Son

Energy losses of Q-balls in Matter, Earth and Detectors

We present a sudy of the interactions of Q-balls with matter, and their energy losses in the earth, for a large range of velocities. These calculations are used to computethe fractional geometrical acceptance of underground detectors. Furthermore we computed the light yield in liquidscintillators, the ionization in streamer tubes and the Restricted Energy Loss in nuclear track detectors.Comment: 8 pages, Invited talk at COSMO99, ICTP-Trieste September 199

Stochastic gravitational waves backgrounds: a probe for inflationary and non-inflationary cosmology

Physical scenarios, leading to highly energetic stochastic gravitational waves backgrounds (for frequencies ranging from the $\mu$Hz up to the GHz) are examined. In some cases the typical amplitude of the logarithmic energy spectrum can be even eight orders of magnitude larger than the ordinary inflationary prediction. Scaling violations in the frequency dependence of the energy density of the produced gravitons are discussed.Comment: 7 pages in Latex styl

Making Baryons Below the Electroweak Scale

I describe a new way for baryogenesis to proceed, which evades many of the problems of GUT and electroweak scenarios. If the reheat temperature after inflation is below the electroweak scale, neither GUT baryon production nor traditional electroweak baryogenesis can occur. However, non-thermal production of sphaleron configurations via preheating could generate the observed baryon asymmetry of the universe. Such low scale baryon production is particularly attractive since it evades a number of strong constraints on reheating from gravitino and moduli production.Comment: 9 pages, uses RevTeX, to appear in the proceedings of COSMO-99, International Workshop on Particle Physics and the Early Univers

The most energetic particles in the universe

Several issues related to the lensing of ultra-high energy cosmic rays by the Galactic magnetic field are discussed.Comment: Plenary talk given by E. Roulet at COSMO99, Trieste, Oct. 199

Relic abundance of dark matter particles: new formulation and new result of abundance calculation

A new theoretical framework for computation of the relic abundance of cold dark matter particles such as LSP is presented and some generic features of new results are discussed. The most important is a generalization of the Boltzmann equation to include off-shell effects and its thermal average over cosmic medium. It is shown that at very low temperatures, much below the mass of annihilating particles, equilibrium abundance is suppressed only by powers of temperature instead of the exponential Boltzmann factor. This change gives a larger relic abundance when heavy particles freeze out at these low temperatures.Comment: 7 pages, LATEX file. Talk given at COSMO9