An abundance analysis of two carbon-rich proto-planetary nebulae: IRAS Z02229 + 6208 and IRAS 07430 + 1115

In this paper, we present an LTE abundance analysis of two new proto-planetary nebulae, IRAS Z02229 + 6208 and IRAS 07430+1115, based on high-resolution (R ≈ 55,000) optical echelle spectra. Results show that both stars are metal-poor ([Fe/H] = -0.5) and overabundant in C, N, and s-process elements. The average elemental abundances are [C/Fe] = +0.8, [N/Fe] = +1.2, and [s-process/Fe] = + 1.4 for IRAS Z02229 + 6208, and [C/Fe] = + 0.6, [N/Fe] = + 0.4, and [s-process/ Fe] = +1.6 for IRAS 07430+1115. These abundances suggest that the stars have experienced nucleo-synthesis on the asymptotic giant branch (AGB), and the resultant products of CNO, 3α, and s-process reactions were brought to the photosphere during shell flashes and deep mixing episodes during the AGB phase of their evolution. Of major significance is the measurement of a high Li abundance in both stars, log ∈(Li) ≈ 2.3 and 2.4 for IRAS Z02229 + 6208 and IRAS 07430 + 1115, respectively. This may be the result of hot bottom burning, below the deep convective zone. We also present an analysis of the circumstellar molecular (C2 and CN) and atomic (Na I and K I) absorption spectra of both stars. We derive rotational temperatures, column densities, and envelope expansion velocities using molecular C2 Phillips and CN Red system bands. The values derived for expansion velocities, 8-14 km s-1, are typical of the values found for post-AGB stars. IRAS 07430 + 1115 is unusual in that it shows P Cygni-shaped C2 emission profiles in the spectra of the circumstellar envelope. A minimum distance for IRAS Z02229 + 6208, determined from interstellar Na I lines, suggests that it is evolved from an intermediate-mass star. Including these two stars, the number of post-AGB stars for which clear C, N, and s-process elemental overabundances are found rises to eight. IRAS Z02229 + 6208 is known to possess the 21 μm emission feature in its mid-infrared spectrum; these results support the idea that all 21 μm emission stars are carbon-rich post-AGB stars

Using H2 Emission to Study the Fast Wind in Proto-Planetary Nebulae

We present the results of a high-resolution H 2 imaging and spectroscopic study of four bipolar proto-planetary nebulae: IRAS 16594-4656, Hen 3-401, Rob 22, and IRAS 17150-3224. These reveal the locations and kinematics of the H 2 emission and the shaping of the nebulae by their collimated fast winds. © 2006 International Astronomical Union.link_to_subscribed_fulltex

A Radial Velocity and Light Curve Study of Pulsations and Binarity in Proto-Planetary Nebulae

We have investigated pulsations and searched for binarity in 7 bright proto-planetary nebulae. All are found to pulsate, with dominant periods of 39−132 days. However, no strong evidence of binarity is found in any of them. This implies that any binary companion must have either a very long period (>30 yr) or low mass (<0.2 Msun). This appears to rule out Roche lobe overflow as a contribution to the shaping of the surrounding nebula

Effect of Nanosilica Additions on Belite Cement Pastes Held in Sulfate Solutions

4 pages.-- Final full-text version of the paper available at: http://dx.doi.org/10.1111/j.1551-2916.2007.02034.x.Fly Ash Belite Cement (FABC) pastes with and without nanosilica additions have been prepared and maintained in sulfate solutions (Na2SO4 0.5M) for 180 days. The mechanical performance and the changes in microstructure have been monitored at 28, 90, and 180 days by compressive strength, X-ray diffraction (XRD), and 29Si MAS NMR measurements. We have found that, unexpectedly, and contrary to what happens in Ordinary Portland Cements (OPC), the addition of nanosilica particles induces an initial decline in the compressive strength of the samples. Only in samples maintained for a long time (180 days) does the nanosilica addition improve the mechanical properties. Our XRD and 29Si NMR experiments have revealed that although nanosilica additions trigger the consumption of Belite phases, this is not always accompanied by formation of longer calcium–silicate–hydrate (C–S–H) gel structures. Only at a long time (180 days), and due to a mechanism that seems to be controlled by the pH of the samples, do the nanosilica additions lead to high-polymerized C–S–H gels.This work was financially supported by the Spanish Government (Projects no. MAT 2002-04023-CO1-CO2-CO3 and MAT2005-03890).Peer reviewe

Organic matter in space: from star dust to the Solar System

Organic compounds of high degree of complexity are now known to be widespread in the Universe, ranging from objects in our Solar System to distant galaxies. Through the techniques of millimeter-wave spectroscopy, over 140 molecules have been identified through their rotational transitions. Space infrared spectroscopy has detected the stretching and bending modes of compounds with aromatic and aliphatic structures. Analyses of samples of meteorites, comets, asteroids, and interplanetary dust also revealed a rich content of organic substances, some of which could be of extra-solar origin. We review the current state of understanding of the origin, evolution, nature, and distribution of organic matter in space. Also discussed are a number of unexplained astronomical phenomena whose origins could be traced to organic carriers. © 2008 Springer Science+Business Media B.V.link_to_subscribed_fulltex