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355 results on '"Lattanzio, John C."'

101. `\delta \mu mixing' on the Red Giant Branch

Author

Angelou, George, primary, Lattanzio, John C., additional, Church, Ross, additional, Stancliffe, Richard, additional, Dearborn, David, additional, Smith, Graeme H, additional, Tout, C.A., additional, and Smith, Verne V, additional

Published
2011
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109. DIVISION IV / WORKING GROUP ABUNDANCES IN RED-GIANTS

Author

Lattanzio, John C., primary, Denissenkov, Pavel A., additional, Gallino, Roberto, additional, Hron, Josef, additional, Jørgensen, Uffe Gråe, additional, Kwok, Sun, additional, van Loon, Jacobus Th., additional, Smith, Verne V., additional, Tout, Christopher, additional, Wing, Robert F., additional, and Zinner, Ernst K., additional

Published
2008
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112. News on Deep Mixing

Author

Lattanzio, John C., primary, Dearborn, Davis S. P., additional, Eggleton, Peter P., additional, Guandalini, Roald, additional, Palmerini, Sara, additional, and Busso, Maurizio, additional

Published
2008
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114. DIVISION IV / WG: ABUNDANCES IN RED GIANTS

Author

Lattanzio, John C., primary, Denissenkov, Pavel A., additional, Gallino, Roberto, additional, Hron, Josef, additional, Jorgensen, Uffae G., additional, Kahane, Claudine, additional, Kwok, Sun, additional, van Loon, Jacobus Th., additional, Smith, Verne V., additional, Tout, Christopher, additional, Wing, Robert F., additional, and Zinner, Ernst, additional

Published
2007
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117. Single Star Progenitors for Type Ia Supernovae

Author

Tout, Christopher A., primary, Wickramasinghe, Dayal T., additional, Lattanzio, John C., additional, Stancliffe, Richard J., additional, Houdek, Guenter, additional, Martin, Rebecca G., additional, and Tout, Christopher A., additional

Published
2007
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124. Working Group on Abundances in Red Giants

Author

Lattanzio, John C., primary, Denissenkov, Pavel, additional, Gallino, Roberto, additional, Hron, Josef, additional, Jørgensen, Uffe Graae, additional, Kahane, Claudine, additional, Kwok, Sun, additional, Smith, Verne, additional, Tout, Christopher, additional, Wing, Robert F., additional, and Zinner, Ernst, additional

Published
2005
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127. On the origin of fluorine in the Milky Way

Author

Renda, Agostino, primary, Fenner, Yeshe, additional, Gibson, Brad K., additional, Karakas, Amanda I., additional, Lattanzio, John C., additional, Campbell, Simon, additional, Chieffi, Alessandro, additional, Cunha, Katia, additional, and Smith, Verne V., additional

Published
2004
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129. Structural and Nucleosynthetic Evolution of Metal-poor & Metal-free Low and Intermediate Mass Stars.

Author

Campbell, Simon W. and Lattanzio, John C.

Subjects
STELLAR evolution, STELLAR luminosity function, STELLAR magnitudes, NUCLEOSYNTHESIS, COSMOCHEMISTRY, GALACTIC halos
Abstract

We report on an investigation into stellar evolution and nucleosynthesis in the low and extremely low metallicity regime, including models of stars with a pure Big Bang composition (i.e. Z = 0). The metallicity range of the extremely metal- poor (EMP) models we have calculated is -6.5<[Fe/H]<-3.0, whilst our models are in the mass rang 0.85⊙. Many of the EMP and Z = 0 models experience violent evolutionary episodes not seen at higher metallicities. We refer to these events as ‘Dual Flashes’ since they are characterised by peaks in the hydrogen and helium burning luminosities occurring at roughly the same time. Some of the material processed by these events is later dredged up by the convective envelope, causing significant surface pollution. These events have been reported by previous studies, so our results reaffirm their occurrence—at least in 1D stellar models. The novelty of this study is that we have calculated the entire evolution of the Z = 0 and EMP models, from the ZAMS to the end of the TPAGB, including detailed nucleosynthesis. We have also calculated the nucleosynthetic yields, which will soon be available in electronic format. Although subject to many uncertainties these are, as far as we are aware, the only yields available in this mass and metallicity range. In this paper we briefly describe some of the results in the context of abundance observations of EMP halo stars. This work formed part of SWC's PhD thesis (completed in March 2007) and a series of subsequent papers will describe the results of the study in more detail. [ABSTRACT FROM AUTHOR]

Published
2008
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134. Super- and massive AGB stars - IV. Final fates - initial-to-final mass relation.

Author

Doherty, Carolyn L., Gil-Pons, Pilar, Siess, Lionel, Lattanzio, John C., and Lau, Herbert H. B.

Subjects
NEUTRON stars, WHITE dwarf stars, SUPERGIANT stars, STELLAR mass, GRAVITATIONAL collapse
Abstract

We explore the final fates of massive intermediate-mass stars by computing detailed stellar models from the zero-age main sequence until near the end of the thermally pulsing phase. These super-asymptotic giant branch (super-AGB) and massive AGB star models are in the mass range between 5.0 and 10.0 M⊙ for metallicities spanning the range Z = 0.02-0.0001. We probe the mass limits Mup, Mn and Mmass, the minimum masses for the onset of carbon burning, the formation of a neutron star and the iron core-collapse supernovae, respectively, to constrain the white dwarf/electron-capture supernova (EC-SN) boundary. We provide a theoretical initial-to-final mass relation for the massive and ultra-massive white dwarfs and specify the mass range for the occurrence of hybrid CO(Ne) white dwarfs. We predict EC-SN rates for lower metallicities which are significantly lower than existing values from parametric studies in the literature. We conclude that the EC-SN channel (for single stars and with the critical assumption being the choice of mass-loss rate) is very narrow in initial mass, at most 0.2 M⊙. This implies that between ~2 and 5 per cent of all gravitational collapse supernova are EC-SNe in the metallicity range Z = 0.02-0.0001. With our choice for mass-loss prescription and computed core growth rates, we find, within our metallicity range, that CO cores cannot grow sufficiently massive to undergo a Type 1.5 SN explosion. [ABSTRACT FROM AUTHOR]

Published
2015
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146. Chemical enrichment by Wolf–Rayet and asymptotic giant branch stars.

Author

Dray, Lynnette M., Tout, Christopher A., Karakas, Amanda I., and Lattanzio, John C.

Subjects
WOLF-Rayet stars, COSMIC abundances
Abstract

ABSTRACT We present theoretical models of Wolf–Rayet (WR) stars for two different sets of mass-loss rates. We compare with observed properties of WR stars and discuss implications for the enrichment of the interstellar medium in both cases. Sets of stellar yields for these stars together with corresponding yields from new models of asymptotic giant branch (AGB) stars are presented and discussed. We find carbon enrichment from WR stars to be on a level comparable to or greater than that from AGB stars for most scenarios. The models predict well the surface abundances and number ratios of WR stars but a population of binaries is needed if the models are to reproduce simultaneously both the observed mass-loss rates and positions on the Hertzsprung–Russell diagram. [ABSTRACT FROM AUTHOR]

Published
2003
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148. Compulsory Deep Mixing of 3He and CNO Isotopes in the Envelopes of Low-Mass Red Giants

Author

Eggleton, Peter P., P, David S., and Lattanzio, John C.

Abstract

Three-dimensional stellar modeling has enabled us to identify a deep-mixing mechanism that must operate in all low-mass giants. This mixing process is not optional, and is driven by a molecular weight inversion created by the 3He(3He,2p)4He reaction. In this paper we characterize the behavior of this mixing, and study its impact on the envelope abundances. It not only eliminates the problem of 3He overproduction, reconciling stellar and big bang nucleosynthesis with observations, but solves the discrepancy between observed and calculated CNO isotope ratios in low-mass giants, a problem of more than three decades standing. This mixing mechanism, which we call " "\delta d m mixing," operates rapidly (relative to the nuclear timescale of overall evolution, ~108 yr) once the hydrogen-burning shell approaches the material homogenized by the surface convection zone. In agreement with observations, Population I stars between 0.8 and 2.0 "M_{\odot M develop 12C/13C ratios of "14.5\pm 14.5 +- 1.5, while Population II stars process the carbon to ratios of "4.0\pm 4.0 +- 0.5. In stars less than 1.25 "M_{\odot M, this mechanism also destroys 90%-95% of the 3He produced on the main sequence.

Published
2008

149. Three-dimensional Numerical Experimentation on the Core Helium Flash of Low-Mass Red Giants

Author

P, David S., Lattanzio, John C., and Eggleton, Peter P.

Abstract

We model the core helium flash in a low-mass red giant using Djehuty, a fully three-dimensional (3D) code. The 3D structures were generated from converged models obtained during the one-dimensional (1D) evolutionary calculation of a 1 M star. Independently of which starting point we adopted, we found that after some transient relaxation the 3D model settled down with a briskly convecting He-burning shell that was not very different from what the 1D model predicted.

Published
2006

150. Reaction Rate Uncertainties and the Production of 19F in Asymptotic Giant Branch Stars

Author

Lugaro, Maria, Ugalde, Claudio, Karakas, Amanda I., Gorres, Joachim, Wiescher, Michael, Lattanzio, John C., and Cannon, Robert C.

Abstract

We present nucleosynthesis calculations and the resulting 19F stellar yields for a large set of models with different masses and metallicity. During the asymptotic giant branch (AGB) phase, 19F is produced as a consequence of nucleosynthesis occurring during the convective thermal pulses and also during the interpulse periods if protons from the envelope are partially mixed in the top layers of the He intershell (partial mixing zone). We find that the production of fluorine depends on the temperature of the convective pulses, the amount of primary 12C mixed into the envelope by third dredge-up, and the extent of the partial mixing zone. Then we perform a detailed analysis of the reaction rates involved in the production of 19F and the effects of their uncertainties. We find that the major uncertainties are associated with the 14C(a, g)18O and 19F(a, p)22Ne reaction rates. For these two reactions we present new estimates of the rates and their uncertainties. In both cases the revised rates are lower than previous estimates. The effect of the inclusion of the partial mixing zone on the production of fluorine strongly depends on the very uncertain 14C(a, g)18O reaction rate. The importance of the partial mixing zone is reduced when using our estimate for this rate. Overall, rate uncertainties result in uncertainties in the fluorine production of about 50% in stellar models with mass [?]3 M and of about a factor of 7 in stellar models of mass [?]5 M. This larger effect at high masses is due to the high uncertainties of the 19F(a, p)22Ne reaction rate. Taking into account both the uncertainties related to the partial mixing zone and those related to nuclear reactions, the highest values of 19F enhancements observed in AGB stars are not matched by the models. This is a problem that will have to be revised by providing a better understanding of the formation and nucleosynthesis in the partial mixing zone, as well as in relation to reducing the uncertainties of the 14C(a, g)18O reaction rate. At the same time, the possible effect of cool bottom processing at the base of the convective envelope should be included in the computation of AGB nucleosynthesis. This process could, in principle, help to match the highest 19F abundances observed by decreasing the C/O ratio at the surface of the star, while leaving the 19F abundance unchanged.

Published
2004

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