Social program:Welcome Reception - Sunday evening (31st Jan)
Location: Foyer of the Green Chemical Futures building
Monash University, Clayton Campus
Excursion & Conference dinner - Wednesday (3rd Feb)
Location: Phillip Island
Constraints on the EOS from nuclear structure and ab-initio theory
We use properties of doubly magic nuclei and ab initio calculations of low-density neutron matter to constrain Skyrme equations of state for neutron-rich conditions. All of these properties are consistent with a Skyrme functional form and a neutron-matter equation of state that depends on three parameters.With a reasonable range for the neutron-matter effective mass, the values of the two other Skyrme parameters are well constrained. This leads to predictions for other quantities.
Observational constraints on the dense matter equation of state (slides)
I shall review observational constraints on the dense matter equation of state and on the mass-radius relation for neutron stars. In addition to the observed distribution of neutron star masses, observations of photospheric expansion during thermally unstable H/He burning and quiescent thermal emission from accreting neutron stars constrain neutron star masses and radii. These in turn constrain the symmetry energy of matter at super-saturation densities.
The evolution of massive stars: dependence of the yields on rotation and metallicity.
I will briefly review our latest set of models that extend in mass between 13 and 120 Msun, in metallicity between 0>=[Fe/H]>=-3 and three initial equatorial rotational velocities: 0, 150 and 300 Km/s.
Super-AGB stars - Lives, Deaths and Element production (slides)
I will talk about a selection of factors that determine the final fates of super-AGB stars. I will also give a brief description of yields from super-AGB stars.
Implications of binary evolution (slides)
Interacting binary stars have a significant impact on the nature of observed stellar populations and they have important consequences for the occurrence rates of electron-capture supernovae and the formation of Super-AGB stars. We will then compare these predictions to observations of supernova progenitors and unusual transients found in recent surveys. Showing how these places limits on the nature of electron capture progenitors. Finally we will discuss how it may be possible to gain constraints on the number of core-collapse vs electron capture SN there are by examining the kick velocities that neutron stars achieve after core-collapse.
Carbon burning in SAGB stars (slides)
We explore the detailed and broad properties of carbon burning in Super Asymptotic Giant Branch (SAGB) with a comprehensive grid of MESA models. The location of first carbon ignition, quenching location of the carbon burning flames and flashes, angular frequency of the carbon core, and carbon core mass are studied as a function of the ZAMS mass, initial rotation rate, and mixing parameters such as convective overshoot, semiconvection, thermohaline and angular momentum transport. We find the properties of carbon burning in SAGB models are not a strong function of the initial rotation profile, but are a sensitive f unction of the strength of overshoot mixing. Increasing the amount of overshoot decreases the initial mass needed for off center and center carbon ignitions. Carbon burning flames show a range of morphologies, which vary as a function of initial mass and convective overshoot strength, with either a series of flashes or a flame which can propagate inwards towards the core. We find that only systems with overshoot mixing strengths >0.01 and ZAMS masses in the range of 7.2-8.0 solar masses can carbon burning be quenched a significant distance from the center. These results have implications for the formation rate of hybrid C-O-Ne WDs, postulated as progenitors of Type Iax SN.
Probing the lower limit of core-collapse: Direct detections of SN progenitors in the local Universe (slides)
Over the past decade, the combination of the Hubble Space Telescope and ground based adaptive optics has led to the identification of a handful of progenitors of core-collapse supernovae in pre-explosion images of their host galaxies. These detections have confirmed that red supergiants above about 8 solar masses explode as hydrogen rich supernovae. However, the progenitors of other supernova types have remained elusive. I will review our current understanding of supernova progenitors from an observational perspective, with a particular focus on the fate of stars at the lower extremum of core-collapse.
Camilla Juul HANSEN
Unveiling the chemical origin of stars through nucleosynthetic and observational studies (slides)
Determining the origin and nuclear formation processes taking place in stellar progenitors that are long gone is a still standing task. Comparing the gases ejected in binary systems that have now dissolved or gases from long gone supernovae to observations may help us understand these formation processes. Actually, this challenge can only be answered by comparing high-resolution, detailed observations to state-of-the-art model predictions. In this talk I will report on the progress and short comings that stellar observations face in the quest of finding and understanding the nature of the progenitor stars that through various nuclear formation processes created the gases the low-mass observed stars consist of. Progenitor stars of particular interest are asymptotic giant branch stars, and faint core collapse supernovae. The carbon enhanced metal-poor (CEMP) stars are of particular interest since they can be observed throughout the Galactic chemical evolution - they are thought to be amongst the first stars, and their closely related carbon enhanced metal-rich (CH) stars are observed at slightly subsolar metallicities. Understanding the variety in origin and enrichment of these stars are is important in the grand picture of Galactic chemical evolution as well as in nuclear astrophysics.
Nucleosynthesis from multi-D simulations of iron-core supernovae (slides)
The collapse of the iron core of a massive star leads to the creation of both a neutron star and a supernova shockwave. Brought back to life by neutrino heating, the development of the shockwave is inextricably linked to multi-dimensional fluid flows, with large scale hydrodynamic instabilities allowing successful explosions that spherical symmetry would prevent. The importance of the neutrino interactions and the multi-dimensional fluid flows that they drive have often been ignored when the nucleosynthesis that occurs in these explosions is discussed. I will present results from simulations of successful explosions using our CHIMERA code, and discuss how the multi-dimensional character of the explosions directly impacts the development of the explosion and the nucleosynthesis that results from these supernovae.
Metal-rich AGB models and yields (slides)
The chemical evolution of the Universe is governed by the chemical yields from stars, which in turn is determined primarily by the initial stellar mass. Stars less massive than about 10 solar mass experience recurrent mixing events on the giant branches that can significantly change the surface composition of the envelope. Here I discuss results from new stellar nucleosynthesis predictions of metal-rich AGB models, which includes models up to the CO core limit. In particular, I highlight my "wish list" of observations that would be helpful in order to constrain stellar models of intermediate-mass AGB stars and super-AGB stars.
Chemical evolution models and chemodynamical simulations for understanding super-AGB stars and various supernovae
Chemical evolution of galaxies can provide useful constraints on stellar evolution, supernova physics, and nucleosynthesis. I will show chemical evolution models with the contribution from super-AGB stars and electron-capture supernovae, comparing to the observed elemental abundance ratios in the Milky Way. Chemodynamical simulation is more advanced model that can naturally include inhomogeneous chemical enrichment and can predict the scatters of elemental abundances. I show the simulations of a Milky-Way type galaxy and a dwarf spheroidal galaxy. With the same simulation code, but for a cosmological volume (cosmological simulations), I predict the supernova rates include electron-capture supernovae and Type Iax supernovae.
Metal-poor stars towards the Galactic bulge: a mixed bag of chemical enrichments (slides)
The bulge is one of the oldest, yet very metal-rich Galactic components suggesting that it experienced early, rapid chemical enrichment. Yet, the first, metal-poor stars to have formed in the Universe are predicted to be found in this central region of the Milky Way. I will present results from our endeavour to detect and characterize signatures from such stars. The chemical abundances of our candidates (at [Fe/H] of -1.5 to -2.6 dex) vastly overlap with those of halo stars and our sample also contains one CEMP-s and a CH-star - the first detections of such objects in the bulge. While we do not see any evidence of Population III enrichment in our sample, the chemical abundance patterns still give a deep insight into the dominant enrichment mechanisms in the early phases of galaxy assembly, also in terms of pollution from massive AGB stars.
Weak rates for ECSN progenitor evolution and nucleosynthesis (slides)
Weak explosions: shock formation and mass ejection
In low-mass progenitors, core collapse can be preceded by intense burning flashes. These may correspond to intense pre-explosion phases of mass loss inferred in some SN light curves. I will consider three aspects of mass ejection by intense acoustic pulses and weak pre-explosions: shock formation from a strong acoustic pulse, the strengthening of a weak shock, and the ejection of matter by shock emergence. In the case of non-spherical shock breakout, the dynamics of mass ejection can be very different from the spherical case.
Light-curve properties of electron-capture supernovae (slides)
I will discuss theoretically predicted light-curve properties of electron-capture supernovae. Especially, most electron-capture supernova progenitors are presumed to be super-AGB stars when they explode, and their large radii and mass-loss rates can strongly affect their light curves. I will compare theoretical light-curve predictions with observed light curves and discuss which supernovae may be related to electron-capture events.
The redshift interval probed by the z filter of DECam is 6.0 < z < 7.2 and ~465 Mpc, comoving. Given the field of view of DECam, our LBG selection criteria probe roughly 1x10^8 Mpc. Observationally, Cooke et al. have found the z~2-4 super-luminous supernova rate to be ~4x10.7 Mpc/yr. This is higher than at low-z, and is expected to continue to increase with redshift. Using a detection window simulation at our sensitivity and the z~2-4 rate, we expect to discover 4+ super-luminous supernovae at z~6-7 per semester.
Electron Capture Supernova Explosion Models -Explosion Dynamics and Nucleosynthesis
While the actual prevalence of electron-capture supernovae (ECSNe) is far from known, they are arguably the one supernova channel for which we best understand the engine and the explosion dynamics. Recent simulations have consistently shown that electron capture supernova explode by the neutrino-driven mechanism with energies of the order of 10^50 erg without the need to boost neutrino heating by convection. In this talk, I shall review the peculiar explosion dynamics of electron capture supernovae and discuss how these may lead to specific nucleosynthetic fingerprints (which include a so-called .weak r-process. up to silver and palladium). I will also discuss the remaining uncertainties in ECSN explosion dynamics and nucleosynthesis that need to be addressed in the future.
Transition from Electron Capture to Iron Core-Collapse Supernovae: Progenitor's Evolutions and Optical Signatures of Explosions
We study the transition from super-AGB star to massive star. A propagating neon-oxygen burning shell is common to both the most massive electron capture supernova (EC-SN) progenitors and the lowest mass iron-core collapse supernova (FeCCSN) progenitors. Of the models that ignite neon burning off-center, the 9.5 Msun model will evolve to an FeCCSN after the neon-burning shell propagates to the center. The neon-burning shell in the 8.8 Msun model, however, fails to reach the center as the URCA process and an extended region of low Y_e in the outer part of the core begin to dominate the late evolution; the model evolves to an EC-SN. This is a new evolutionary path to EC-SN (`failed massive star'). We show that the two evolutionary fates (EC-SN and FeCCSN) are separated by the dynamics of the neon and oxygen burning shells and the behavior of the URCA process. We have also computed an 8.75 Msun super-AGB star through its entire thermal pulse phase until electron captures on 20Ne begin at its center, and examine the differences between the pre-SN evolution and progenitor structure of the 8.75 and 8.8 Msun models. We present two supernova progenitor structures for EC-SNe (a super-AGB star and a `failed massive star') and one FeCCSN progenitor structure from a 12 Msun star. We discuss how the different pathways to collapse affect the pre-supernova structure and compare our results to the observed neutron star mass distribution. Finally, we demonstrate the light curves of EC-SNe and FeCCSNe to compare the observation including the Crab supernova 1054.
Nucleosynthesis from Low-Mass Supernovae
Based on recent progress in understanding neutrino emission and neutrino-driven explosion of core-collapse supernovae near the mass threshold for such events, nucleosynthesis in these low-mass supernovae is reviewed, with particular emphasis on neutrino-induced production. Implications for observations at low metallicities and meteoritic studies of the early solar system are discussed.
Evolution of massive single and binary stars - their fate and remnants
The final fate of massive stars, the type of explosion and the remnant they leave behind, is mostly governed by the masses of their helium cores and hydrogen envelopes in the latest stages of evolution. While for single stars wind mass loss is the only channel to reduce their mass, stars that are a member of a binary system are also assumed to loose their hydrogen envelope due to Roche lobe overflow or a common envelope phase after core hydrogen burning. We aim at assigning the ZAMS masses of stars in the range 15-45 solar masses to their remnant masses and in quantifying their compactness predict their most likely remnants, neutron stars or black holes.
Convective mixing and nucleosynthesis in super-AGB stars
We present the massive and super-AGB star yield calculations of light and heavy elements from the NuGrid collaboration. In these calculations we adopt a hybrid post-processing approach to accurately simulate hot-bottom burning conditions and hot dredge-up. New stellar evolution simulations of super-AGB stars with convective boundary mixing do not only show hot dredge-up but also the possibility of a new type of H-ingestion episode in the dredge-out phase and during thermal pulses. H-ingestion into convective He-shell flash regions have been identified as a nucleosynthesis site of the i process. A number of observational signatures of i-process have been suggested, such as some CEMP-r/s stars or the post-AGB star Sakurai's object. We have identified a new potential site for i process. Rapidly accreting WDs are usually associated with the single-degenerate progenitor channel of SN type Ia. New multi-cycle He-shell flash stellar evolution simulations of such objects show very small or even negative retention rates as well as H-ingestion flashes and i-process nucleosynthesis. Another possible implication of convective boundary mixing in super-AGB stars is the formation of hybrid CONe WDs in which URCA processes may be activated that introduce significant uncertainties for such SN Ia progenitor models.
Birthrates of accretion-induced collapse neutron stars from binary evolution models (slides)
The details of the final stages of stellar evolution for stars in the mass range ~7-10 Msun remain somewhat uncertain. Introducing interacting binary stars into the mix complicates things further, though allows us to explore the formation of neutron stars originating from a wider variety of formation scenarios. I will present preliminary results showing physical properties for accretion induced collapse progenitors arising from interacting binary star systems that host one (or more) white dwarf(s). The most interesting finding is that the nature of the donor star at time of collapse has a non-negligible dependence on the assumed common envelope formalism. The trends found in the simulated data can guide future studies that aim to fill the gaps within the 'peak luminosity' vs. 'timescale' parameter space for transient events.
The Evolution of ONe White Dwarfs towards Accretion-Induced Collapse (slides)
The thermal and compositional evolution of the center of an accreting oxygen-neon white dwarf is driven by weak reactions that occur in electron-degenerate conditions. I will discuss a series of calculations that use the MESA stellar evolution code to follow this evolution. These include previously neglected effects such as Urca-process cooling and are able to reach length-scales that directly connect full-star simulations to past studies of the onset of the collapse process.
Evolution of the SAGB progenitors of electron capture supernovae (slides)
In this talk, I will review the main features of the evolution of super-AGB stars, constrain their mass range and present the binary scenarios that can also lead to the formation of electron capture supernovae.
Neutrino-induced nucleosynthesis in Supernovae
In Core-Collapse supernova, the ejected material is irradiated by large neutrino fluxes. These neutrinos affect the explosive nucleosynthesis induced by the supernova shock and have an impact on the final composition of the ejecta. We have studied the neurtrino process with a new set of neutrino-nucleus cross sections assuming neutrino energies in agreement with state-of-the-art SN simulations. We have put a special focus on the production of radioactive isotopes.
Pre-Supernova Mass Loss and the Extremes of the Core Collapse Mass Range
I will discuss issues relating ecSNe to other types of SNe from an observational perspective. I will first discuss observed statistics of different types of SNe, and what they imply about mass loss, binary interaction, and ranges of initial mass, and I will discuss some ways that ecSNe factor into the analysis. I will then review different types of transients that may be the observed counterparts of ecSNe, including underluminous SNe II-P, a subgroup of SN impostors often referred to as SN2008S-like objects, and the subclass of Type IIn events called SNe IIn-P. In particular, I will discuss a possible connection between SNe IIn-P and the Crab Nebula. Last, I will discuss observational evidence and ideas for violent pre-SN mass ejection events that seem to occur at high initial masses, and interestingly for this meeting, also at relatively low masses. In both cases these events may be related to final nuclear burning sequences in these stars.
Beta transition rates and EOS for supernova with the knowledge of Nuclear Physics (slides)
The Production of p/nuclei in SNIa and SNII at different metallicities: Clues for Galactic Chemical Evolution
The bulk of p-isotopes is created in the 'gamma processes', mainly by sequences of photodisintegrations and beta decays in explosive conditions in core collapse supernovae or in Type Ia supernovae (SNIa). We explore single degenerate SNIa in the framework of 2D and 3D delayed detonation explosion models. We present a detailed study of p-process nucleosynthesis occuring in SNIa with s-process seeds at different metallicities. Using a classical chemical evolution code we give estimates of the contribution of SNIa to the solar p-process composition, including the radiogenic 92Nb, 146Sm, and 97,98Tc. Uncertainties in nuclear physics will also be discussed. First reults for 3D SNIa (Seitenzahl et al. 2013) p-process calculations will be presented, with comparison with 2D calculations, and demonstrating the dependence of some p-isotopes to the treatment of the explosion. Assuming that about 70% of normal SNe Ia are due to the progenitor and explosive mechanism considered here, we find that SNe Ia can be responsible for at least 50% of the p-nuclei abundances in the Solar System. We also analyzed the contribution to the Solar System abundance of p-nuclei from core collapse supernovae, using the most updated SNII models (from A. Heger and from M. Pignatari) and a refined grid in metallicity. We explore photodisintegrations and alpha rich freeze-out contribution, and we show that small contribution can be done from SNII to the bulk of p-nuclei. Instead significant contribution can come from these astrophysical sources to the lightest p-nuclei.