Oxygen and light element synthesis by neutron-capture reactions in metal-free and extremely metal-poor AGB stars

The metal-free (Pop. III) and extremely metal-poor (EMP) stars of low- and intermediate-masses experience mixing of hydrogen into the helium convection during the early TP-AGB phase, differently from the meal-rich stars. We study the nucleosynthesis in the helium convective zone with 13C formed from mixed protons as neutron source by using a nuclear network from H through S. In the absence or scarcity of the pristine metals, the neutron-recycling reactions, 12C(n,g)13C(a,n)16O and also 16O(n,g)17O(a,n)20Ne promote the synthesis of O and light elements, including their neutron-rich isotopes and the odd atomic number elements. Based on the results, we demonstrate that the peculiar abundance patterns of C through Al observed for the three most iron-deficient, carbon-rich stars can be reproduced in terms of the nucleosynthesis in Pop. III, AGB stars in the different mass range. We argue that these three stars were born as the low-mass members of Pop. III binaries and later subject to the surface pollution by the mass transfer in the binary systems. It is also shown that the AGB nucleosynthesis with hydrogen mixing explains the abundances of C, O, Na, Mg and Al observed for most of carbon-enhanced EMP (CEMP) stars, including all CEMP-s stars with s-process elements. In addition the present results are used to single out other nucleosynthetic signatures of early generations of stars.Comment: 46 pages, 13 figures, accepted for PAS

The Stellar Abundances for Galactic Archeology (SAGA) Database - Compilation of the Characteristics of Known Extremely Metal-Poor Stars

We describe the construction of a database of extremely metal-poor (EMP) stars in the Galactic halo whose elemental abundances have been determined. Our database contains detailed elemental abundances, reported equivalent widths, atmospheric parameters, photometry, and binarity status, compiled from papers in the recent literature that report studies of EMP halo stars with [Fe/H] < -2.5. The compilation procedures for this database have been designed to assemble the data effectively from electronic tables available from online journals. We have also developed a data retrieval system that enables data searches by various criteria, and permits the user to explore relationships between the stored variables graphically. Currently, our sample includes 1212 unique stars (many of which are studied by more than one group) with more than 15000 individual reported elemental abundances, covering all of the relevant papers published by December 2007. We discuss the global characteristics of the present database, as revealed by the EMP stars observed to date. For stars with [Fe/H] < -2.5, the number of giants with reported abundances is larger than that of dwarfs by a factor of two. The fraction of carbon-rich stars (among the sample for which the carbon abundance is reported) amount to ~30 % for [Fe/H] < -2.5. We find that known binaries exhibit different distributions of orbital period, according to whether they are giants or dwarfs, and also as a function of metallicity, although the total sample of such stars is still quite small.Comment: 24 pages, 10 figures, accepted by PASJ, final version. The SAGA database is available at http://saga.sci.hokudai.ac.j

Oxidized phagosomal NOX2 complex is replenished from lysosomes

Contains fulltext : 177861.pdf (publisher's version ) (Open Access)In dendritic cells, the NADPH oxidase 2 complex (NOX2) is recruited to the phagosomal membrane during antigen uptake. NOX2 produces reactive oxygen species (ROS) in the lumen of the phagosome that kill ingested pathogens, delay antigen breakdown and alter the peptide repertoire for presentation to T cells. How the integral membrane component of NOX2, cytochrome b558 (which comprises CYBB and CYBA), traffics to phagosomes is incompletely understood. In this study, we show in dendritic cells derived from human blood-isolated monocytes that cytochrome b558 is initially recruited to the phagosome from the plasma membrane during phagosome formation. Cytochrome b558 also traffics from a lysosomal pool to phagosomes and this is required to replenish oxidatively damaged NOX2. We identified syntaxin-7, SNAP23 and VAMP8 as the soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins mediating this process. Our data describe a key mechanism of how dendritic cells sustain ROS production after antigen uptake that is required to initiate T cell responses

Neutron-capture nucleosynthesis in the He-flash convective zone in extremely metal-poor stars

We investigate the nucleosynthesis in the helium flash convective zone, triggered by the hydrogen mixing, for extremely metal-poor stars of low and intermediate mass. Mixed hydrogen is converted into neutron through 12C(p,γ) 13N(e +ν) 13C(α ,n) 16O and the doubly neutron-recycling reactions 12C(n,γ) 13C(α,n) 16O(n,γ) 17O(α,n) 20Ne operate. In addition to oxygen and neon, not only light elements from sodium through phosphorus but also the s-process elements, heavier than iron, are synthesized via successive neutron captures with 20Ne as seeds even in the stars originally devoid of metals. We follow the both the doubly neutron-recycling reactions and the s-process nucleosynthesis up to Pb and Bi by varying model parameters such as the amount of mixed 13C. The resultant abundance patterns is shown to reproduce the observed enhancement not only of oxygen, the light elements but also Sr observed from HE 0107-5240 and HE 1327-2326. © 2006 American Institute of Physics.SCOPUS: cp.pInternational Symposium on Origin of Matter and Evolution of Galaxies 2005: New Horizon of Nuclear Astrophysics and Cosmology; Tokyo; Japan; 8 November 2005 through 11 November 2005.info:eu-repo/semantics/publishe

Nucleosynthetic signatures of pop.III survivors and the origin of HE0107-5240 and HE1327-2326

The discoveries of two extremely iron-poor stars with [Fe/H]<-5, HE0107-5240 and HE1327-2326 provided the great opportunities of verifying whether these stars are the survivors of the first generation stars; the very weak lines of detected metals in their atmospheres can be extrinsic source that is the accretion from interstellar gas or from binary companion, rather than intrinsic one. In this work, we explore the possibility that these stars were born in binary systems from the primordial clouds by considering the results of stellar evolution and nucleosynthesis in metal-free models of low to intermediate mass AGB stars. Observed abundance patterns for these 2 stars are in agreement with the results and can be explained by the binary scenario that observed stars disguise their surface abundances by the mass transfer in the binary system. In particular, we first demonstrated the reproduction of Sr without large enhancement of Ba through the neutron capture reactions in the helium flash convective region of AGB models without any iron seeds for s-process. The apparent lack of stars in -5 < [Fe/H] < -4 may suggest the effect of dilution by the surface convection at the red giant branch. If this is true, other Pop.III survivors can be discovered at the main sequence having [Fe/H] ∼ -3, whose surface abundances are changed by the mass transfer from evolved companions in binary systems. © 2006 American Institute of Physics.SCOPUS: cp.pinfo:eu-repo/semantics/publishe

Glypican-1 modulates the angiogenic and metastatic potential of human and mouse cancer cells.

Cells isolated from many types of human cancers express heparin-binding growth factors (HBGFs) that drive tumor growth, metastasis, and angiogenesis. The heparan sulfate proteoglycan glypican-1 (GPC1) is a coreceptor for HBGFs. Here we show that both cancer cell-derived and host-derived GPC1 are crucial for efficient growth, metastasis, and angiogenesis of human and mouse cancer cells. Thus downregulation of GPC1 in the human pancreatic cancer cell line PANC-1, using antisense approaches, resulted in prolonged doubling times and decreased anchorage-independent growth in vitro as well as attenuated tumor growth, angiogenesis, and metastasis when these cells were transplanted into athymic mice. Moreover, athymic mice that lacked GPC1 exhibited decreased tumor angiogenesis and metastasis following intrapancreatic implantation with either PANC-1 or T3M4 human pancreatic cancer cells and fewer pulmonary metastases following intravenous injection of murine B16-F10 melanoma cells. In addition, hepatic endothelial cells isolated from these mice exhibited an attenuated mitogenic response to VEGF-A. These data indicate that cancer cell- and host-derived GPC1 are crucial for full mitogenic, angiogenic, and metastatic potential of cancer cells. Thus targeting GPC1 might provide new avenues for cancer therapy and for the prevention of cancer metastasis