Thermonuclear flashes of hydrogen and helium accreted onto neutron stars produce the frequently observed Type I X-ray bursts. It is the current paradigm that almost all material burns in a burst, ...after which it takes hours to accumulate fresh fuel for the next burst. In rare cases, however, bursts are observed with recurrence times as short as minutes. We present the first one-dimensional multi-zone simulations that reproduce this phenomenon. Bursts that ignite in a relatively hot neutron star envelope leave a substantial fraction of the fuel unburned at shallow depths. In the wake of the burst, convective mixing events driven by opacity bring this fuel down to the ignition depth on the observed timescale of minutes. There, unburned hydrogen mixes with the metal-rich ashes, igniting to produce a subsequent burst. We find burst pairs and triplets, similar to the observed instances. Our simulations reproduce the observed fraction of bursts with short waiting times of ∼30%, and demonstrate that short recurrence time bursts are typically less bright and of shorter duration.
Hans Bethe contributed in many ways to our understanding of the supernovae that happen in massive stars, but, to this day, a first principles model of how the explosion is energized is lacking. ...Nevertheless, a quantitative theory of nucleosynthesis is possible. We present a survey of the nucleosynthesis that occurs in 32 stars of solar metallicity in the mass range 12–
120
M
⊙
. The most recent set of solar abundances, opacities, mass loss rates, and current estimates of nuclear reaction rates are employed. Restrictions on the mass cut and explosion energy of the supernovae based upon nucleosynthesis, measured neutron star masses, and light curves are discussed and applied. The nucleosynthetic results, when integrated over a Salpeter initial mass function (IMF), agree quite well with what is seen in the sun. We discuss in some detail the production of the long lived radioactivities,
26Al and
60Fe, and why recent model-based estimates of the ratio
60
Fe
/
26
Al
are overly large compared with what satellites have observed. A major source of the discrepancy is the uncertain nuclear cross sections for the creation and destruction of these unstable isotopes.
Nebular spectra of pair-instability supernovae Jerkstrand, A; Smartt, S. J; Heger, A
Monthly Notices of the Royal Astronomical Society,
01/2016, Letnik:
455, Številka:
3
Journal Article
Recenzirano
Odprti dostop
If very massive stars (M ≳ 100 M⊙) can form and avoid too strong mass-loss during their evolution, they are predicted to explode as pair-instability supernovae (PISNe). One critical test for ...candidate events is whether their nucleosynthesis yields and internal ejecta structure, being revealed through nebular-phase spectra at t ≳ 1 yr, match those of model predictions. Here, we compute theoretical spectra based on model PISN ejecta at 1–3 yr post-explosion to allow quantitative comparison with observations. The high column densities of PISNe lead to complete gamma-ray trapping for t ≳ 2 yr which, combined with fulfilled conditions of steady state, leads to bolometric supernova luminosities matching the 56Co decay. Most of the gamma-rays are absorbed by the deep-lying iron and silicon/sulphur layers. The ionization balance shows a predominantly neutral gas state, which leads to emission lines of Fe i, Si i, and S i. For low-mass PISNe, the metal core expands slowly enough to produce a forest of distinct lines, whereas high-mass PISNe expand faster and produce more featureless spectra. Line blocking is complete below ∼5000 Å for several years, and the model spectra are red. The strongest line is typically Ca ii λλ7291, 7323, one of few lines from ionized species. We compare our models with proposed PISN candidates SN 2007bi and PTF12dam, finding discrepancies for several key observables and thus no support for a PISN interpretation. We discuss distinct spectral features predicted by the models, and the possibility of detecting pair-instability explosions among non-superluminous supernovae.
The production of the heavy stable proton-rich isotopes between 74Se and 196Hg-the p nuclides-is due to the contribution from different nucleosynthesis processes, activated in different types of ...stars. Whereas these processes have been subject to various studies, their relative contributions to Galactic chemical evolution (GCE) are still a matter of debate. Here we investigate for the first time the nucleosynthesis of p nuclides in GCE by including metallicity and progenitor mass-dependent yields of core-collapse supernovae (ccSNe) into a chemical evolution model. We used a grid of metallicities and progenitor masses from two different sets of stellar yields and followed the contribution of ccSNe to the Galactic abundances as a function of time. In combination with previous studies on p-nucleus production in thermonuclear supernovae (SNIa), and using the same GCE description, this allows us to compare the respective roles of SNeIa and ccSNe in the production of p-nuclei in the Galaxy. The γ process in ccSN is very efficient for a wide range of progenitor masses (13 M -25 M ) at solar metallicity. Since it is a secondary process with its efficiency depending on the initial abundance of heavy elements, its contribution is strongly reduced below solar metallicity. This makes it challenging to explain the inventory of the p nuclides in the solar system by the contribution from ccSNe alone. In particular, we find that ccSNe contribute less than 10% of the solar p nuclide abundances, with only a few exceptions. Due to the uncertain contribution from other nucleosynthesis sites in ccSNe, such as neutrino winds or -rich freeze out, we conclude that the light p-nuclides 74Se, 78Kr, 84Sr, and 92Mo may either still be completely or only partially produced in ccSNe. The γ-process accounts for up to twice the relative solar abundances for 74Se in one set of stellar models and 196Hg in the other set. The solar abundance of the heaviest p nucleus 196Hg is reproduced within uncertainties in one set of our models due to photodisintegration of the Pb isotopes 208,207,206Pb. For all other p nuclides, abundances as low as 2% of the solar level were obtained.
ABSTRACT X-ray bursts are thermonuclear flashes on the surface of accreting neutron stars, and reliable burst models are needed to interpret observations in terms of properties of the neutron star ...and the binary system. We investigate the dependence of X-ray burst models on uncertainties in (p, γ), ( , γ), and ( , p) nuclear reaction rates using fully self-consistent burst models that account for the feedbacks between changes in nuclear energy generation and changes in astrophysical conditions. A two-step approach first identified sensitive nuclear reaction rates in a single-zone model with ignition conditions chosen to match calculations with a state-of-the-art 1D multi-zone model based on the Kepler stellar evolution code. All relevant reaction rates on neutron-deficient isotopes up to mass 106 were individually varied by a factor of 100 up and down. Calculations of the 84 changes in reaction rate with the highest impact were then repeated in the 1D multi-zone model. We find a number of uncertain reaction rates that affect predictions of light curves and burst ashes significantly. The results provide insights into the nuclear processes that shape observables from X-ray bursts, and guidance for future nuclear physics work to reduce nuclear uncertainties in X-ray burst models.
Context. Mergers of two stellar-origin black holes are a prime source of gravitational waves and are under intensive investigation. One crucial ingredient in their modeling has been neglected: ...pair-instability pulsation supernovae with associated severe mass loss may suppress the formation of massive black holes, decreasing black-hole-merger rates for the highest black-hole masses. Aims. We demonstrate the effects of pair-instability pulsation supernovae on merger rate and mass using populations of double black-hole binaries formed through the isolated binary classical evolution channel. Methods. The mass loss from pair-instability pulsation supernova is estimated based on existing hydrodynamical calculations. This mass loss is incorporated into the StarTrack population synthesis code. StarTrack is used to generate double black-hole populations with and without pair-instability pulsation supernova mass loss. Results. The mass loss associated with pair-instability pulsation supernovae limits the Population I/II stellar-origin black-hole mass to 50 M⊙, in tension with earlier predictions that the maximum black-hole mass could be as high as 100 M⊙. In our model, neutron stars form with mass 1−2 M⊙. We then encounter the first mass gap at 2−5 M⊙ with the compact object absence due to rapid supernova explosions, followed by the formation of black holes with mass 5−50 M⊙, with a second mass gap at 50−135 M⊙ created by pair-instability pulsation supernovae and by pair-instability supernovae. Finally, black holes with masses above 135 M⊙ may potentially form to arbitrarily high mass limited only by the extent of the initial mass function and the strength of stellar winds. Suppression of double black-hole-merger rates by pair-instability pulsation supernovae is negligible for our evolutionary channel. Our standard evolutionary model, with the inclusion of pair-instability pulsation supernovae and pair-instability supernovae, is fully consistent with the Laser Interferometric Gravitational-wave Observatory (LIGO) observations of black-hole mergers: GW150914, GW151226, and LVT151012. The LIGO results are inconsistent with high (≳ 400 km s-1) black hole (BH) natal kicks. We predict the detection of several, and up to as many as ~60, BH-BH mergers with a total mass of 10−150 M⊙ (most likely range: 20−80 M⊙) in the forthcoming ~60 effective days of the LIGO O2 observations, assuming the detectors reach the optimistic target O2 sensitivity.
Type I X-ray bursts are thermonuclear explosions on the surface of accreting neutron stars. Hydrogen rich X-ray bursts burn protons far from the line of stability and can release energy in the form ...of neutrinos from β-decays. We have estimated, for the first time, the neutrino fluxes of Type I bursts for a range of initial conditions based on the predictions of a 1D implicit hydrodynamics code, Kepler, which calculates the complete nuclear reaction network. We find that neutrino losses are between and 0.14 of the total energy per nucleon, , depending upon the hydrogen fraction in the fuel. These values are significantly below the 35% value for neutrino losses often adopted in recent literature for the rp-process. The discrepancy arises because it is only at β-decays that of energy is lost due to neutrino emission, whereas there are no neutrino losses in and reactions. Using the total measured burst energies from Kepler for a range of initial conditions, we have determined an approximation formula for the total energy per nucleon released during an X-ray burst, , where is the average hydrogen mass fraction of the ignition column, with an rms error of . We provide a detailed analysis of the nuclear energy output of a burst and find an incomplete extraction of mass excess in the burst fuel, with 14% of the mass excess in the fuel not being extracted.
The mass distribution of Population III stars Fraser, M; Casey, A. R; Gilmore, G ...
Monthly Notices of the Royal Astronomical Society,
06/2017, Letnik:
468, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
Extremely metal-poor (EMP) stars are uniquely informative on the nature of massive Population III stars. Modulo a few elements that vary with stellar evolution, the present-day photospheric ...abundances observed in EMP stars are representative of their natal gas cloud composition. For this reason, the chemistry of EMP stars closely reflects the nucleosynthetic yields of supernovae from massive Population III stars. Here we collate detailed abundances of 53 EMP stars from the literature and infer the masses of their Population III progenitors. We fit a simple initial mass function (IMF) to a subset of 29 of the inferred Population III star masses, and find that the mass distribution is well represented by a power-law IMF with exponent
$\alpha = 2.35^{+0.29}_{-0.24}$
. The inferred maximum progenitor mass for supernovae from massive Population III stars is
$M_{\rm {max}} = 87^{+13}_{-33}$
M⊙, and we find no evidence in our sample for a contribution from stars with masses above ∼120 M⊙. The minimum mass is strongly consistent with the theoretical lower mass limit for Population III supernovae. We conclude that the IMF for massive Population III stars is consistent with the IMF of present-day massive stars and there may well have formed stars much below the supernova mass limit that could have survived to the present day.
ABSTRACT
We present 3D full-sphere supernova simulations of non-rotating low-mass (∼9 M⊙) progenitors, covering the entire evolution from core collapse through bounce and shock revival, through shock ...breakout from the stellar surface, until fallback is completed several days later. We obtain low-energy explosions (∼0.5–1.0 × 1050 erg) of iron-core progenitors at the low-mass end of the core-collapse supernova (LMCCSN) domain and compare to a super-AGB (sAGB) progenitor with an oxygen–neon–magnesium core that collapses and explodes as electron-capture supernova (ECSN). The onset of the explosion in the LMCCSN models is modelled self-consistently using the vertex-prometheus code, whereas the ECSN explosion is modelled using parametric neutrino transport in the prometheus-HOTB code, choosing different explosion energies in the range of previous self-consistent models. The sAGB and LMCCSN progenitors that share structural similarities have almost spherical explosions with little metal mixing into the hydrogen envelope. A LMCCSN with less second dredge-up results in a highly asymmetric explosion. It shows efficient mixing and dramatic shock deceleration in the extended hydrogen envelope. Both properties allow fast nickel plumes to catch up with the shock, leading to extreme shock deformation and aspherical shock breakout. Fallback masses of $\mathord {\lesssim }\, 5\, \mathord {\times }\, 10^{-3}$ M⊙ have no significant effects on the neutron star (NS) masses and kicks. The anisotropic fallback carries considerable angular momentum, however, and determines the spin of the newly born NS. The LMCCSN model with less second dredge-up results in a hydrodynamic and neutrino-induced NS kick of >40 km s−1 and a NS spin period of ∼30 ms, both not largely different from those of the Crab pulsar at birth.
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