Tur, Clarisse, Heger, Alexander, Austin, Sam M.
We have studied the sensitivity to variations in the the triple alpha and 12C(a,g)16O reaction rates of the production of 26Al, 44Ti, and 60Fe in core-collapse supernovae. We used the KEPLER code to...
Primordial Core-Collapse Supernovae and the Chemical Abundances of Metal-Poor Stars (2009)
Joggerst, C. C., Almgren, A., Bell, J., Heger, Alexander, Whalen, Daniel, Woosley, S. E.
The inclusion of rotationally-induced mixing in stellar evolution can alter the structure and composition of presupernova stars. We survey the effects of progenitor rotation on nucleosynthetic yields...
Mixing in Zero and Solar Metallicity Supernovae (2008)
Joggerst, C. C., Woosley, S. E., Heger, Alexander
Two-dimensional simulations of mixing and fall back in non-rotating massive stars have been carried out using realistic initial models for the presupernova star and assuming standard spherically...
The Impact of Neutrino Magnetic Moments on the Evolution of Massive Stars (2008)
Heger, Alexander, Friedland, Alexander, Giannotti, Maurizio, Cirigliano, Vincenzo
We explore the sensitivity of massive stars to neutrino magnetic moments. We find that the additional cooling due to the neutrino magnetic moments bring about qualitative changes to the structure and...
Tur, Clarisse, Heger, Alexander, Austin, Sam M.
We have studied the sensitivity of s-process nucleosynthesis in massive stars to +/- 2sigma variations in the rates of the triple alpha and 12C(a,g)16O reactions. We simulated the evolution of...
Detailed Abundances for 28 Metal-poor Stars: Stellar Relics in the Milky Way (2008)
Lai, David K., Bolte, Michael, Johnson, Jennifer A., Lucatello, Sara, Heger, Alexander, Woosley, S. E.
We present the results of an abundance analysis for a sample of stars with $-4
Nucleosynthesis and Evolution of Massive Metal-Free Stars (2008)
Heger, Alexander, Woosley, S. E.
The evolution and explosion of metal-free stars with masses 10--100 solar masses are followed, and their nucleosynthetic yields, light curves, and remnant masses determined. When the supernova yields...
The Molecular Hydrogen Deficit in Gamma-Ray Burst Afterglows (2008)
Whalen, Daniel, Prochaska, Jason X., Heger, Alexander, Tumlinson, Jason
Recent analysis of five gamma-ray burst (GRB) afterglow spectra reveal the absence of molecular hydrogen absorption lines, a surprising result in light of their large neutral hydrogen column...
First Stars III Conference Summary (2008)
O'Shea, Brian W., McKee, Christopher F., Heger, Alexander, Abel, Tom
The understanding of the formation, life, and death of Population III stars, as well as the impact that these objects had on later generations of structure formation, is one of the foremost issues in...
Massive Stars: The Pre-Supernova Evolution Of Internal And Circumstellar Structure (2007)
Norbert Langer, Alexander Heger
. We review new developments in the theory of massive stars and their circumstellar environments, considering the evolution from the main sequence to the supernova explosion. Our focus is --- for...
Models of Type I X-ray Bursts from GS 1826-24: A Probe of rp-Process Hydrogen Burning (2007)
Heger, Alexander, Cumming, Andrew, Galloway, Duncan K., Woosley, Stanford E.
The X-ray burster GS 1826-24 shows extremely regular Type I X-ray bursts whose energetics and recurrence times agree well with thermonuclear ignition models. We present calculations of sequences of...
Pulsational pair instability as an explanation for the most luminous supernovae (2007)
Woosley, S. E., Blinnikov, S., Heger, Alexander
The extremely luminous supernova SN 2006gy challenges the traditional view that the collapse of a stellar core is the only mechanism by which a massive star makes a supernova, because it seems too...
Detecting primordial stars (2007)
Scannapieco, Evan, Ferrara, Andrea, Heger, Alexander, Madau, Piero, Schneider, Raffaella, Woosley, Stan
We study the detectability of primordial metal-free stars. Cosmological enrichment is a local process that takes place over an extended redshift range. While the duration of this transition depends...
Tur, Clarisse, Heger, Alexander, Austin, Sam M.
We explore the dependence of pre-supernova evolution and supernova nucleosynthesis yields on the uncertainties in helium burning reaction rates. Using the revised solar abundances of Lodders (2003)...
The Lack of Gamma-Ray Bursts from Population III Binaries (2006)
Belczynski, Krzysztof, Bulik, Tomasz, Heger, Alexander, Fryer, Chris
We study the evolution of first star (Population III) binaries. Under specific conditions, these stars may produce high redshift gamma-ray bursts (GRBs). We demonstrate that the occurrence rate of...
Sensitivity of Type I X-Ray Bursts to rp-Process Reaction Rates (2006)
Amthor, A. Matthew, Galaviz, Daniel, Heger, Alexander, Sakharuk, Alexander, Schatz, Hendrik, Smith, Karl
First steps have been taken in a more comprehensive study of the dependence of observables in Type I X-ray bursts on uncertain (p,gamma) reaction rates along the rp-process path. We use the multizone...
The Supernova Gamma-Ray Burst Connection (2006)
Woosley, Stan, Heger, Alexander
The chief distinction between ordinary supernovae and long-soft gamma-ray bursts (GRBs) is the degree of differential rotation in the inner several solar masses when a massive star dies, and GRBs are...
Germanium in damped Lyman-alpha systems and copper connection (2006)
Gallino, Roberto, Pignatari, M., Bisterzo, S., Prochaska, Jason X., Fenner, Y., Heger, Alexander, ...
From the analysis of recent high-resolution spectroscopy data of Cu in unevolved galactic stars at various metallicities, as compared with nucleosynthesis predictions in massive stars exploding as...
Germanium in damped Lyman-alpha systems and copper connection (2006)
Gallino, Roberto, Pignatari, M., Bisterzo, S., Prochaska, Jason X., Fenner, Y., Heger, Alexander, ...
From the analysis of recent high-resolution spectroscopy data of Cu in unevolved galactic stars at various metallicities, as compared with nucleosynthesis predictions in massive stars exploding as...
Heger, Alexander, Cumming, Andrew, Woosley, Stanford E.
We investigate marginally stable nuclear burning on the surface of accreting neutron stars as an explanation for the mHz quasi-periodic oscillations (QPOs) observed from three low mass X-ray...
Detecting Primordial Stars (2005)
Scannapieco, Evan, Ferrara, Andrea, Heger, Alexander, Madau, Piero, Schneider, Raffaella, Woosley, Stan
We study the detectability of primordial metal-free stars. Cosmological enrichment is a local process that takes place over an extended redshift range. While the duration of this transition depends...
The Progenitor Stars of Gamma-Ray Bursts (2005)
Woosley, Stan, Heger, Alexander
Those massive stars that, during their deaths, give rise to gamma-ray bursts (GRBs) must be endowed with an unusually large amount of angular momentum in their inner regions, one to two orders of...
The Detectability of Pair-Production Supernovae at z < 6 (2005)
Scannapieco, Evan, Madau, Piero, Woosley, Stan, Heger, Alexander, Ferrara, Andrea
Nonrotating, zero metallicity stars with initial masses 140 < M < 260 solar masses are expected to end their lives as pair-production supernovae (PPSNe), in which an electron-positron pair-production...
Which Massive stars are Gamma-Ray Burst Progenitors? (2005)
Petrovic, Jelena, Langer, Norbert, Yoon, Sung-Chul, Heger, Alexander
The collapsar model for gamma-ray bursts requires three essential ingredients: a massive core, removal of the hydrogen envelope, and enough angular momentum in the core. We study current massive star...
Binary Merger Progenitors for Gamma-Ray Bursts and Hypernovae (2004)
Fryer, Chris L., Heger, Alexander
The collapsar model, the now leading model for the engine behind gamma-ray bursts and hypernovae, requires that a star collapses to form a black hole surrounded by an accretion disk of high-angular...
Pulsational Analysis of the Cores of Massive Stars and its Relevance to Pulsar Kicks (2004)
Murphy, Jeremiah, Burrows, Adam, Heger, Alexander
The mechanism responsible for the natal kicks of neutron stars continues to be a challenging problem. Indeed, many mechanisms have been suggested, and one hydrodynamic mechanism may require large...
Evolution and explosion of very massive primordial stars (2002)
Heger, Alexander, Woosley, Stan, Baraffe, Isabelle, Abel, Tom
The spin-up of contracting red supergiants (1998)
Heger, Alexander, Langer, Norbert
We report on a mechanism which may lead to a spin-up of the surface of a rotating single star leaving the Hayashi line, which is much stronger than the spin-up expected from the mere contraction of...
The Evolution of Surface Parameters of Rotating Massive Stars (1997)
Langer, Norbert, Heger, Alexander
We summarize the present status of the predictions of massive star models for the evolution of their surface properties. After discussing luminosity, temperature and chemical composition, we focus on...
Heger, Alexander, Jeannin, Laurent, Langer, Norbert, Baraffe, Isabelle
We investigate the pulsational properties of RSG models --- which we evolve from ZAMS masses in the range 10 to $20 \Msun$ --- by means of linear and non-linear calculations. We find period and...