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  Papers • Papers of 2008
Fluorine in carbon-enhanced metal-poor stars: a binary scenario
M. Lugaro, S. E. de Mink, R. G. Izzard, S. W. Campbell, A. I. Karakas, S. Cristallo, O. R. Pols, J. C. Lattanzio, O. Straniero, R. Gallino, T. C. Beers
A super-solar fluorine abundance was observed in the carbon-enhanced metal-poor (CEMP) star HE 1305+0132 ([F/Fe]=+2.90, [Fe/H]=-2.5). We propose that this observation can be explained using a binary model of mass transfer from an asymptotic giant branch (AGB) star companion.
Fluorine vs (Carbon+Nitrogen) for HE 1305+0132 vs that in our models.
Astronomy and Astrophysics, Volume 484, Issue 3, 2008, pp.L27-L30
Gamma-Ray Bursts from tidally spun-up Wolf-Rayet stars?
R. G. Detmers, N. Langer, Ph. Podsiadlowski, R.G. Izzard
The outcome of the evolutionary calculations for helium star-compact object binaries with two different mass-loss rates.
The collapsar model requires rapidly rotating Wolf-Rayet stars as progenitors of long gamma-ray bursts. However, Galactic Wolf-Rayet stars rapidly lose angular momentum due to their intense stellar winds. We find that the simple scenario - i.e., the Wolf-Rayet star being tidally spun up and producing a collapsar - does not occur at solar metallicity and may only occur with low probability at low metallicity.
Astronomy and Astrophysics, Volume 484, Issue 3, 2008, pp.831-839
The effect of massive binaries on stellar populations and supernova progenitors
J. J. Eldridge, R. G. Izzard and C. A. Tout.
We have calculated a large set of detailed binary models and tested them against observed stellar populations to compare the number of blue/red supergiants and Wolf-Rayet stars at different metallicities. We have also estimated the relative rate of type Ib/c to type II supernovae. We find, with an interacting binary fraction of about two thirds, that we obtain better agreement between our models and observations than with single stars.
Supernova type Ib/c to type II ratio for single vs binary stars and compared to observations for our models and those of the Geneva group.
Massive Stars as Cosmic Engines, Proceedings of IAU Symposium 250, pp.179-184
The Mysterious R Stars
R. G. Izzard, C. S. Jeffery, J. Lattanzio
The R stars are a rare class of K-type giant carbon stars. Canonical stellar evolutionary theory cannot explain their existence, yet they have been observed for more than a century. The early-R stars, the warmest in the R class, are enhanced in 12C, 13C and 14N relative to the Sun, but not in s-processes elements or oxygen, and are all single stars. We test the idea that binary mergers lead to the formation of the early-R stars by a comparison of binary population synthesis model results with observations.
Proceedings of the IXth Torino Workshop on AGB Stars, Perugia, 2008
Modelling the evolution and nucleosynthesis of carbon-enhanced metal-poor stars
O. R. Pols, R. G. Izzard, M. Lugaro, S. E. de Mink
We present the results of binary population simulations of carbon-enhanced metal-poor (CEMP) stars. We show that nitrogen and fluorine are useful tracers of the origin of CEMP stars, and conclude that the observed paucity of very nitrogen-rich stars puts strong constraints on possible modifications of the initial mass function at low metallicity. The large number fraction of CEMP stars may instead require much more efficient dredge-up from low-metallicity asymptotic giant branch stars.
The Art of Modeling (sic) Stars in the 21st Century, Proceedings of IAU Symposium 252
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