Atomic and Molecular Data for Stellar Physics: Former Successes and Future Challenges

This review highlights current (and future) hot topics in astrophysics where atomic or molecular input data are (or will be) essential, with special emphasis on topics relating to nucleosynthesis and cosmochemistry. We first discuss issues (like the abundances of oxygen and iron in the Sun, and that of lithium in post-AGB stars) where the use of poor-quality atomic or molecular data have led to spurious astrophysical puzzles which sparked fancy astrophysical models or theories. We then address issues where the advent of new instruments (like the ultraviolet high-resolution spectrographs--GHRS onboard HST, Keck-HRS or VLT-UVES--or future infrared satellites) calls for new and accurate atomic or molecular data.Comment: 20 pages, 12 figures, to appear in Physica Scripta, Topical Issue (Proceedings of the 35th EGAS conference -- European Group for Atomic Spectroscopy

AGB stars in binaries and their progeny

It is currently admitted that an AGB star in a binary system is likely to pollute its companion with carbon- and s-process-rich matter. After the AGB star has faded into an unconspicuous white dwarf, the polluted companion enters the zoo of stars with chemical peculiarities. In this paper, the progeny of AGB stars in binary systems are identified among existing spectroscopic classes (Abell 35-like, binary post-AGB, WIRRing, dwarf Ba and C, subgiant CH, Ba, CH, S, yellow symbiotics) and their filiation is discussed from the properties of their eccentricity -- period diagrams.Comment: Invited review at IAU Symp. 191 (AGB Stars, eds. T. Le Bertre, A. Lebre, C. Waelkens), 10 pages, 2 figures (LaTeX/paspconf.sty). Also available at: http://astro.ulb.ac.be/Htm/ps.ht

The link between symbiotic stars and chemically-peculiar red giants

Barium stars and technetium-poor, extrinsic S stars are binary systems with a white dwarf companion, and with orbital elements similar to those of symbiotic systems. One may thus wonder whether these various families of binary systems involving red giant stars are somehow related. This question is actually twofold: (i) Do barium and binary S stars exhibit some symbiotic activity? (ii) Do symbiotic systems exhibit overabundances of s-process elements like barium and S stars? This paper reviews the current situation regarding these two questions.Comment: 16 pages, 5 figures, to be published in 'Symbiotic Stars Probing Stellar Evolution' (R.L.M. Corradi, J. Mikolajewska, T.J. Mahoney eds.), ASP Conf. Ser. Also available at http://www-astro.ulb.ac.be/Html/ps.html#symbi

Is Amino-Acid Homochirality Due To Asymmetric Photolysis In Space?

Amino acids occurring in proteins are, with rare exceptions, exclusively of the L-configuration. Among the many scenarios put forward to explain the origin of this chiral homogeneity (i.e., homochirality), one involves the asymmetric photolysis of amino acids present in space, triggered by circularly polarized UV radiation. The recent observation of circularly polarized light (CPL) in the Orion OMC-1 star-forming region (Bailey et al. 1998, Science 281, 672) has been presented as providing a strong validation of this scenario. The present paper reviews the situation. It is stressed for example that one important condition for the asymmetric photolysis by CPL to be at the origin of the terrestrial homochirality of natural amino acids is generally overlooked, namely, the asymmetric photolysis should favour the L-enantiomer for ALL the primordial amino acids involved in the genesis of life (i.e., biogenic amino acids). Although this condition is probably satisfied for aliphatic amino acids, some non-aliphatic amino acids like tryptophan and proline may violate the condition and thus invalidate the asymmetric photolysis scenario, assuming they were among the primordial amino acids. Alternatively, if CPL photolysis in space is indeed the source of homochirality of amino acids, then tryptophan and proline may be crossed out from the list of biogenic amino acids.Comment: To appear in Space Science Reviews, 11 pages, 1 figure (LaTeX

Cosmic abundances: The impact of stellar duplicity

The mass-transfer scenario links chemical peculiarities with stellar duplicity for an increasing number of stellar classes (classical and dwarf barium stars, subgiant and giant CH stars, S stars without technetium, yellow symbiotic stars, WIRRING stars, Abell-35-like nuclei of planetary nebulae...). Despite these successes, the mass-transfer scenario still faces several problems: What is the mass-transfer mode? Why orbital elements of dwarf barium stars do not fully match those of the classical barium stars? What is the origin of the few non-binary stars among dwarf barium stars? The paper reviews these open questions.Comment: 14 pages, 4 figures, to appear in `Cosmic Abundances as Records of Stellar Evolution and Nucleosynthesis', edited by F.N. Bash, T.G. Barnes, ASP Conf. Ser., in pres

Circumstellar shells and mass loss rates: Clues to the evolution of S stars

It is the purpose of this paper to rediscuss the circumstellar properties of S stars and to put these properties in perspective with our current understanding of the evolutionary status of S stars, in particular the intrinsic/extrinsic dichotomy. Accordingly, an extensive data set probing the circumstellar environment of S stars (IRAS flux densities, maser emission, CO rotational lines) has been collected and critically evaluated. This data set combines new observations (9 stars have been observed in the CO J=2-1 line and 3 in the CO J=3-2 line, with four new detections) with existing material (all CO and maser observations of S stars published in the literature). The IRAS flux densities of S stars have been re-evaluated by co-adding the individual scans, in order to better handle the intrinsic variability of these stars in the IRAS bands, and possible contamination by Galactic cirrus. Mass loss rates or upper limits have been derived for all S stars observed in the CO rotational lines, and range from < 2 10^{-8} Msun y^{-1} for extrinsic S stars to 10^{-5} Msun y^{-1}. These mass-loss rates correlate well with the K - [12] color index, which probes the dust loss rate, provided that the mass loss rate be larger than 10^{-8} Msun~y^{-1}. Small mass-loss rates are found for extrinsic S stars, consistent with their not being so evolved (RGB or Early-AGB) as the Tc-rich S stars. This result does not support the claim often made in relation with symbiotic stars that binarity strongly enhances the mass-loss rate.Comment: Astronomy & Astrophysics Suppl., 40 pages, 22 figures, 6 tables (LaTeX). Also available at: http://astro.ulb.ac.be/Htm/ps.ht

The Henize sample of S stars. I. The technetium dichotomy

This paper is the first one in a series investigating the properties of the S stars belonging to the Henize sample (205 S stars with delta<-25 deg. and R<10.5) in order to derive the respective properties (like galactic distribution and relative frequencies) of intrinsic (i.e. genuine asymptotic giant branch) S stars and extrinsic (i.e. post mass-transfer binary) S stars. High-resolution (R=30 000 to 60 000) spectra covering the range 4230-4270AA have been obtained for 76 S stars, 8 M stars and 2 symbiotic stars. The 4262AA and 4238AA blends involving a Tc I line were analysed separately and yield consistent conclusions regarding the presence or absence of technetium. Only one `transition' case (Hen 140 = HD 120179, a star where only weak lines of technetium are detectable) is found in our sample. A resolution greater than R =30 000 is clearly required in order to derive unambiguous conclusions concerning the presence or absence of technetium. The Tc/no Tc dichotomy will be correlated with radial velocity and photometric data in a forthcoming paper.Comment: 10 pages, 5 figures, Latex, accepted for publication in Astronomy and Astrophysics main journal. Also available at http://astro.ulb.ac.be

The Effect of Maternal Aldosterone Levels on the Expression of 11B-HSD Isoenzymes in Normal and Hypertensive Rat Placentae

In this project, we developed a Western blotting procedure to semi-quantitate levels of 11β-HSD1 and 11β-HSD2 in whole cell extracts. Then, we applied this technique to analyze the effect of reduced maternal aldosterone levels on the expression of 11β-HSD1 and 11β-HSD2 isoenzymes in the placental tissue in both normal and hypertensive rats. These enzymes control levels of glucocorticoids which compete for aldosterone’s mineralocorticoid receptor. Overstimulation of this receptor results in hypertension. If aldosterone levels decrease, levels of the enzymes controlling active glucocorticoid concentrations might change to compensate for the lowered aldosterone levels. Decreased placental 11β-HSD2 expression could affect hypertension in the offspring. The Western blotting procedure was optimized for the detection of the two isoenzymes in their dimeric forms. The use of multiple protein levels on the blot was useful to obtain a more reliable semi-quantitation. Because of the presence of multiple bands, it was impossible to use an internal beta actin standard to normalize the data from one blot to another. This along with the low expression levels and uneven blot backgrounds made it difficult to obtain enough data on the expression of the two isoenzymes. Very limited data do not support differences in the placental expression of the two isoenzymes when maternal aldosterone levels are lowered

Management control in the transfer pricing tax compliant multinational enterprise

This paper studies the impact of transfer pricing tax compliance on management control system (MCS) design and use within one multinational enterprise (MNE) which employed the same transfer prices for tax compliance and internal management purposes. Our analysis shows immediate effects of tax compliance on the design of organising controls with subsequent effects on planning, evaluating and rewarding controls which reveal a more coercive use of the MCS overall. We argue that modifications to the MCS cannot be understood without an appreciation of the MNEs’ fiscal transfer pricing compliance process