Herwig, Falk, Pignatari, Marco, Woodward, Paul R., Porter, David H., Rockefeller, Gabriel, Fryer, Chris L., ...
We investigate the convective-reactive situation when unprocessed material with a high H abundance is convectively mixed with a He-burning zone, such as a convectively unstable He-burning shell on...
The Hydrodynamic Environment for the s Process in the He-Shell Flash of AGB Stars (2009)
Woodward, Paul R., Porter, David H., Herwig, Falk, Pignatari, Marco, Jayaraj, Jagan, Lin, Pei-Hung
The He-shell flash convection in AGB stars is the site for the high-temperature component of the s-process in low- and intermediate mass giants, driven by the Ne22 neutron source. [...] The upper...
NuGrid: Toward High Precision Double-Degenerate Merger Simulations with SPH in 3D (2008)
Diehl, Steven, Fryer, Christopher L., Hungerford, Aimee, Rockefeller, Gabriel, Bennett, Michael, Herwig, Falk, ...
We present preliminary results from recent high-resolution double-degenerate merger simulations with the Smooth Particle Hydrodynamics (SPH) technique. We put particular emphasis on verification and...
Nucleosynthesis Calculations from Core-Collapse Supernovae (2008)
Fryer, Christopher L., Young, Patrick, Bennett, Michael, Diehl, Steven, Herwig, Falk, Hirschi, Raphael, ...
We review some of the uncertainties in calculating nucleosynthetic yields, focusing on the explosion mechanism. Current yield calculations tend to either use a piston, energy injection, or...
Nucleosynthetic Yields from "Collapsars" (2008)
Rockefeller, Gabriel, Fryer, Christopher L., Young, Patrick, Bennett, Michael, Diehl, Steven, Herwig, Falk, ...
The "collapsar" engine for gamma-ray bursts invokes as its energy source the failure of a normal supernova and the formation of a black hole. Here we present the results of the first...
44Ti and 56Ni in core-collapse supernovae (2008)
Magkotsios, Georgios, Timmes, Francis X., Wiescher, Michael, Fryer, Christopher L., Hungerford, Aimee, Young, Patrick, ...
We investigate the physical conditions where 44Ti and 56Ni are created in core-collapse supernovae. In this preliminary work we use a series of post-processing network calculations with parametrized...
Nucleosynthesis simulations for a wide range of nuclear production sites from NuGrid (2008)
Herwig, Falk, Bennett, Michael, Diehl, Steven, Fryer, Christopher L., Hirschi, Raphael, Hungerford, Aimee, ...
Simulations of nucleosynthesis in astrophysical environments are at the intersection of nuclear physics reaction rate research and astrophysical applications, for example in the area of galactic...
NuGrid: s process in massive stars (2008)
Hirschi, Raphael, Frischknecht, Urs, Thielemann, F. -K., Pignatari, Marco, Bennett, Michael, Diehl, Steven, ...
The s-process production in massive stars at very low metallicities is expected to be negligible due to the low abundance of the neutron source 22Ne, to primary neutron poisons and decreasing iron...
Young, Patrick, Ellinger, Carola I., Timmes, Francis X., Arnett, David, Fryer, Christopher L., Rockefeller, Gabriel, ...
We examine observed heavy element abundances in the Cassiopeia A supernova remnant as a constraint on the nature of the Cas A supernova. We compare bulk abundances from 1D and 3D explosion models and...
Complete nucleosynthesis calculations for low-mass stars from NuGrid (2008)
Pignatari, Marco, Herwig, Falk, Bennett, Michael, Diehl, Steven, Fryer, Christopher L., Hirschi, Raphael, ...
Many nucleosynthesis and mixing processes of low-mass stars as they evolve from the Main Sequence to the thermal-pulse Asymptotic Giant Branch phase (TP-AGB) are well understood (although of course...
Difficulties in Probing Nuclear Physics: A Study of $^{44}$Ti and $^{56}$Ni (2008)
Hungerford, Aimee, Fryer, Christopher L., Timmes, Francis X., Young, Patrick, Bennett, Michael, Diehl, Steven, ...
The nucleosynthetic yield from a supernova explosion depends upon a variety of effects: progenitor evolution, explosion process, details of the nuclear network, and nuclear rates. Especially in...
Patrick Young, Carola I. Ellinger, Frank Timmes, David Arnett, Chris L. Fryer, Gaberiel R. Rockefeller, ...
We examine observed heavy element abundances in the Cassiopeia A supernova remnant as a constraint on the nature of the Cas A supernova. We compare bulk abundances from 1D and 3D explosion models and...
Woodward, Paul, Herwig, Falk, Porter, David, Fuchs, Tyler, Nowatzki, Anthony, Pignatari, Marco
The evolution of the first generations of stars at zero or extremly low metallicity, and especially some crucial properties like the primary N14 production, is charactarized by convective-reactive...
The Formation of Hydrogen Deficient Stars through Common Envelope Evolution (2007)
Diehl, Steven, Fryer, Chris, Herwig, Falk
We present preliminary results from Smooth Particle Hydrodynamics (SPH) simulations of common envelope evolution. We qualitatively compare the interaction between a 0.9M red giant with two different...
Convective and non-convective mixing in AGB stars (2007)
Herwig, Falk, Freytag, Bernd, Fuchs, Tyler, Hansen, James P., Hueckstaedt, Robert M., Porter, David H., ...
We review the current state of modeling convective mixing in AGB stars. The focus is on results obtained through multi-dimensional hydrodynamic simulations of AGB convection, both in the envelope and...
The ejecta of the first probably very massive stars polluted the Big Bang primordial element mix with the first heavier elements. The resulting ultra metal-poor abundance distribution provided the...
On the Connection between Mass Loss and Evolution of C-rich AGB stars (2007)
Mattsson, Lars, Hoefner, Susanne, Wahlin, Rurik, Herwig, Falk
The mass loss properties of carbon AGB stars are not very well constrained at present. A variety of empirical or theoretical formulae with different parameterisations are available in the literature...
Mass Loss Evolution and the Formation of Detached Shells around TP-AGB Stars (2007)
Mattsson, Lars, Hoefner, Susanne, Herwig, Falk
The origin of the so called 'detached shells' around AGB stars is not fully understood, but two common hypotheses state that these shells form either through the interaction of distinct wind phases...
Clayton, Geoffrey C., Geballe, T. R., Herwig, Falk, Fryer, Christopher, Asplund, Martin
We have found that at least seven hydrogen-deficient carbon (HdC) and R Coronae Borealis (RCB) stars, have 16O/18O ratios close to and in some cases less than unity, values that are orders of...
A Search for Nitrogen-Enhanced Metal-Poor Stars (2006)
Johnson, Jennifer A., Herwig, Falk, Beers, Timothy C., Christlieb, Norbert
Theoretical models of very metal-poor intermediate-mass Asymptotic Giant Branch (AGB) stars predict a large overabundance of primary nitrogen. The very metal-poor, carbon-enhanced, s-process-rich...
The Evolution of Central Stars of Planetary Nebulae (2006)
Herwig, Falk, Freytag, Bernd, Werner, Klaus
The evolution of central stars of planetary nebulae can proceed in several distinct ways, either leading to H-deficiency or to H-normal surface composition. Several new simulations of the evolution...
Supernova Fallback: A Possible Site for the r-Process (2006)
Fryer, Chris L., Herwig, Falk, Hungerford, Aimee, Timmes, Frank
The conditions for the leading r-process site candidate, neutrino-driven winds, can not be reproduced self-consistently in current supernova models. For that reason, we investigate an alternate model...
Hydrodynamic simulations of He-shell flash convection (2006)
Herwig, Falk, Freytag, Bernd, Hueckstaedt, Robert M., Timmes, Francis X.
We present the first hydrodynamic, multi-dimensional simulations of He-shell flash convection. Specifically, we investigate the properties of shell convection at a time immediately before the He-...
An Extremely Large Excess of 18O in the Hydrogen-Deficient Carbon Star, HD 137613 (2005)
Clayton, Geoffrey C., Herwig, Falk, Geballe, T. R., Asplund, Martin, Tenenbaum, Emily D., Engelbracht, C. W., ...
We report the discovery of a uniquely large excess of 18O in the hydrogen-deficient carbon (HdC) star, HD 137613, based on a spectrum of the first overtone bands of CO at 2.3-2.4 micron in which...
Rauch, Thomas, Reiff, Elke, Werner, Klaus, Herwig, Falk, Koesterke, Lars, Kruk, Jeff W.
95% of all stars end their lives as white dwarfs. About 20% of the hot post-AGB stars are hydrogen deficient. Most of these are the result of a late helium-shell flash, but the evolutionary status of...
Nuclear Reaction Rates and Carbon Star Formation (2004)
We have studied how the third dredge-up and the carbon star formation in low-mass Asymptotic Giant Branch stars depends on certain key nuclear reaction rates. We find from a set of complete stellar...
Evolution and Yields of Extremely Metal Poor Intermediate Mass Stars (2004)
Intermediate mass stellar evolution tracks from the main sequence to the tip of the AGB for five initial masses (2 to 6Msun) and metallicity Z=0.0001 have been computed. The detailed 1D structure and...
Dredge-up and envelope burning in intermediate mass giants of very low metallicity (2003)
(abbreviated) The evolution of intermediate mass stars at very low metallicity during their final thermal pulse asymptotic giant branch phase is studied in detail. As representative examples models...
Current models for the evolution of AGB stars (2003)
While the basic properties of AGB stellar evolution are well established, comprehensive observational studies of late phases of intermediate mass stars continue to generate puzzles for current...
The s-Process in Rotating Asymptotic Giant Branch Stars (2003)
Herwig, Falk, Langer, Norbert, Lugaro, Maria
(abridged) We model the nucleosynthesis during the thermal pulse phase of a rotating, solar metallicity AGB star of 3M_sun. Rotationally induced mixing during the thermal pulses produces a layer...
Denissenkov, Pavel A., Herwig, Falk
We present full stellar evolution and parametric models of the surface abundance evolution of O16, Ne22, Na23 and the magnesium isotopes in an extremely metal-poor intermediate mass star...
Mixing and the s-process in rotating AGB stars (2003)
Herwig, Falk, Langer, Norbert, Lugaro, Maria
We model the nucleosynthesis during a radiative interpulse phase of a rotating 3Msun Asymptotic Giant Branch (AGB) star. We find an enhanced production of the neutron source species C13 compared to...
s-Process nucleosynthesis in asymptotic giant branch stars : a test for stellar evolution (2003)
Lugaro, Maria, Herwig, Falk, Lattanzio, John, Gallino, Roberto, Straniero, Oscar
s-Process nucleosynthesis in asymptotic giant branch stars : a test for stellar evolution (2003)
Lugaro, Maria, Herwig, Falk, Lattanzio, John, Gallino, Roberto, Straniero, Oscar
s-Process Nucleosynthesis in AGB Stars: A Test for Stellar Evolution (2002)
Lugaro, Maria, Herwig, Falk, Lattanzio, John C., Gallino, Roberto, Straniero, Oscar
[abridged] We study the s-process in AGB stars using three different stellar evolutionary models computed for a 3Msun and solar metallicity star. First we investigate the formation and the efficiency...
Could SiC A+B grains have originated in a post-AGB thermal pulse? (2002)
Herwig, Falk, Amari, Sachiko, Lugaro, Maria, Zinner, Ernst
The carbon and nitrogen isotopic ratios of pre-solar SiC grains of type A+B suggest a proton-limited nucleosynthetic process as encountered, for instance, during the very late thermal pulse of...
Past and future evolution of Sakurai's object (2002)
We present a stellar evolution model sequence of the past and future evolution of the post-AGB born again star Sakurai's object (V4334 Sgr). In order to match the short evolutionary time scale we...
Fe-deficiency in H-deficient post-AGB stars due to n-capture nucleosynthesis (2002)
Herwig, Falk, Lugaro, Maria, Werner, Klaus
H-deficient post-AGB objects, e.g. PG1159 type star K1-16 and born-again AGB star Sakurai's object, have been reported to be significantly iron-deficient. We find that the iron deficiencies expected...
The s-process in rotating AGB stars (2002)
Herwig, Falk, Langer, Norbert, Lugaro, Maria
We discuss the occurrence of the s-process during the radiative interpulse phase of rotating AGB stars. Due to differential rotation, protons are mixed into C12-rich layers after thermal pulses, in...
Wolf-Rayet Central Stars and the Binary Evolution Channel (2002)
De Marco , Orsola, Herwig , Falk, Mac Low, Mordecai Mark, Sandquist , Eric L., Taam , Ronald E.
Single star evolutionary calculations have recently succeeded in reproducing the composition of the hydrogen deficient Wolf-Rayet (WR) central stars of planetary nebula (PN). However, the latest...
The evolutionary time scale of Sakurai's object: A test of convection theory? (2001)
Sakurai's object (V4334 Sgr) is a born again AGB star following a very late thermal pulse. So far no stellar evolution models have been able to explain the extremely fast evolution of this star,...
Modeling the evolution of Sakurai's object (2001)
Sakurai's object is a born again AGB star of the very late thermal pulse flavor. In this contribution I will discuss new models of stellar evolution and nucleosynthesis models of this phase. Two most...
Stellar evolution and nucleosynthesis of Post-AGB Stars (2001)
I discuss recent new models of post-Asymptotic Giant Branch stellar evolution. These models aim to clarify the evolutionary origin and status of a variety of hydrogen-deficient post-AGB stars such as...
A thermal pulse during the post-AGB phase of stellar evolution may lead to a unique mode of light element nucleosynthesis. The stage is set by the ingestion of the unprocessed envelope material into...
Advances in s-process models (2000)
Within the framework of the current models for the slow neutron capture (s) process in Asymptotic Giant Branch (AGB) stars we explore the uncertainties introduced by the assumptions made on stellar...
Formation of the Neutron Donor C13 in AGB Stars by Overshoot and Rotation (2000)
(abridged) Observations clearly show that low-mass AGB stars can provide a nucleosynthesis site of the s-process. Recent stellar evolution models indicate that radiative burning of C13 between...
The evolution of AGB stars with convective overshoot (2000)
The influence of extended convective mixing (overshoot) on asymptotic giant branch stellar evolution is investigated in detail. The extended mixing is treated time-dependently, and the efficiency...
TP-AGB evolution with overshoot for low-mass stars as a function of metallicity (1999)
Herwig, Falk, Bloecker, Thomas, Driebe, Thomas
We give a brief review on the properties of asymptotic giant branch models with overshoot. Then we describe new model calculations with overshoot. Initial masses are ranging from 1 to 3Msun and...
Internal mixing and surface abundance of [WC]-CSPN (1999)
Recent advances in constructing stellar evolution models of hydrogen-deficient post-asymptotic giant branch (AGB) stars are presented. Hydrogen-deficiency can originate from mixing and subsequent...