We investigate the evolution of Type Ib/c supernova (SN Ib/c) progenitors in close binary systems, using new evolutionary models that include the effects of rotation, with initial masses of 12-25 M ...for the primary components, and of single helium stars with initial masses of 2.8-20 M . We find that, despite the impact of tidal interaction on the rotation of primary stars, the amount of angular momentum retained in the core at the presupernova stage in different binary model sequences converges to a value similar to those found in previous single star models. This amount is large enough to produce millisecond pulsars, but too small to produce magnetars or long gamma-ray bursts. We employ the most up-to-date estimate for the Wolf-Rayet mass-loss rate, and its implications for SN Ib/c progenitors are discussed in detail. In terms of stellar structure, SN Ib/c progenitors in binary systems at solar metallicity are predicted to have a wide range of final masses up to about 7 M , with helium envelopes of M He 0.16-1.5 M . Our results indicate that, if the lack of helium lines in the spectra of SNe Ic were due to small amounts of helium (e.g., M He 0.5), the distribution of both initial and final masses of SN Ic progenitors should be bimodal. Furthermore, we find that a thin hydrogen layer (0.001 M M H 0.01 M ) is expected to be present in many SN Ib progenitors at the presupernova stage. We show that the presence of hydrogen, together with a rather thick helium envelope, can lead to a significant expansion of some SN Ib/c progenitors by the time of supernova explosion. This may have important consequences for the shock break-out and supernova light curve. We also argue that some SN progenitors with thin hydrogen layers produced via Case AB/B transfer might be related to Type IIb supernova progenitors with relatively small radii of about 10 R .
Aims. We present a new grid of massive Population III (Pop III) star models including the effects of rotation on the stellar structure and chemical mixing, and magnetic torques for the transport of ...angular momentum. This grid covers the range of mass from 10 to 1000 M⊙, and rotational velocity from zero to 100% of the critical rotation on the zero-age main sequence. Based on the grid, we also present a phase diagram for the expected final fates (i.e., core-collapse supernova, gamma-ray bursts (GRBs) and pair-instability supernovae of diverse types) of rotating massive Pop III stars. Methods. The model grid has been calculated with a stellar evolution code. We adopted the recent calibration made with the VLT-FLAMES data for the overshooting parameter and the chemical mixing efficiency due to rotation. The Spruit-Tayler dynamo was assumed for magnetic torques. Results. Our non-rotating models become redder than the previous models in the literature because of the larger overshooting parameter adopted in this study. In particular, convective dredge-up of the helium core material into the hydrogen envelope is observed in our non-rotating very massive star models (≳200 M⊙), which is potentially important for the chemical yields. On the other hand, the stars become bluer and more luminous with a higher rotational velocity. With the Spruit-Tayler dynamo, our models with a sufficiently high initial rotational velocity can reach the critical rotation earlier and lose more mass as a result, compared to the previous models without magnetic fields. The most dramatic effect of rotation is found with the so-called chemically homogeneous evolution (CHE), which is observed for a limited mass and rotational velocity range. CHE has several important consequences: 1) both primary nitrogen and ionizing photons are abundantly produced; 2) conditions for GRB progenitors are fulfilled for an initial mass range of 13–84 M⊙; 3) pair instability supernovae of type Ibc are expected for 84–190 M⊙; 4) both a pulsational pair instability supernova and a GRB may occur from the same progenitor of ~56–84 M⊙, which might significantly influence the consequent GRB afterglow. We find that CHE does not occur for very massive stars (>190 M⊙), in which case the hydrogen envelope expands to the red-supergiant phase and the final angular momentum is too low to generate any explosive event powered by rotation.
We systematically explore the evolution of the merger of two carbon–oxygen (CO) white dwarfs. The dynamical evolution of a 0.9 M⊙+ 0.6 M⊙ CO white dwarf merger is followed by a 3D smoothed particle ...hydrodynamics (SPH) simulation. The calculation uses a state-of-the-art equation of state that is coupled to an efficient nuclear reaction network that accurately approximates all stages from helium burning up to nuclear statistical equilibrium. We use an elaborate prescription in which artificial viscosity is essentially absent, unless a shock is detected, and a much larger number of SPH particles than earlier calculations. Based on this simulation, we suggest that the central region of the merger remnant can, once it has reached quasi-static equilibrium, be approximated as a differentially rotating CO star, which consists of a slowly rotating cold core and a rapidly rotating hot envelope surrounded by a centrifugally supported disc. We construct a model of the CO remnant that mimics the results of the SPH simulation using a 1D hydrodynamic stellar evolution code and then follow its secular evolution, where we include the effects of rotation on the stellar structure and the transport of angular momentum. The influence of the Keplerian disc is implicitly treated by considering mass accretion from the disc on to the hot envelope. The stellar evolution models indicate that the growth of the cold core is controlled by neutrino cooling at the interface between the core and the hot envelope, and that carbon ignition in the envelope can be avoided despite high effective accretion rates. This result suggests that the assumption of forced accretion of cold matter that was adopted in previous studies of the evolution of double CO white dwarf merger remnants may not be appropriate. Specifically we find that off-centre carbon ignition, which would eventually lead to the collapse of the remnant to a neutron star, can be avoided if the following conditions are satisfied. (1) When the merger remnant reaches quasi-static equilibrium, the local maximum temperature at the interface between the core and the envelope must be lower than the critical limit for carbon ignition. (2) Angular momentum loss from the central merger remnant should not occur on a time-scale shorter than the local neutrino cooling time-scale at the interface. (3) The mass accretion rate from the centrifugally supported disc must be sufficiently low to 10−5 M⊙ yr−1). Our results imply that at least some products of double CO white dwarfs merger may be considered good candidates for the progenitors of Type Ia supernovae. In this case, the characteristic time delay between the initial dynamical merger and the eventual explosion would be ∼105 yr.
Recent models of rotating massive stars including magnetic fields prove it difficult for the cores of single stars to retain enough angular momentum to produce a collapsar and gamma-ray burst. At low ...metallicity, even very massive stars may retain a massive hydrogen envelope due to the weakness of the stellar winds, posing an additional obstacle to the collapsar model. Here, we consider the evolution of massive, magnetic stars where rapid rotation induces almost chemically homogeneous evolution. We find that in this case, the requirements of the collapsar model are rather easily fulfilled if the metallicity is sufficiently small: 1) rapidly rotating helium stars are formed without the need to remove the hydrogen envelope, avoiding mass-loss induced spin-down. 2) Angular momentum transport from the helium core to hydrogen envelope by magnetic torques is insignificant. We demonstrate this by calculating evolutionary models of massive stars with various metallicities, and derive an upper metallicity limit for this scenario based on currently proposed mass loss rates. Our models also suggest the existence of a lower CO-core mass limit of about $10\,{M}_\odot$ – which relates to an initial mass of only about $20\,{M}_\odot$ within our scenario – for GRB production. We argue that the relative importance of the considered GRB progenitor channel, compared to any channel related to binary stars, may increase with decreasing metallicity, and that this channel might be the major path to GRBs from first stars.
Context. Millisecond pulsars (MSPs) are generally believed to be old neutron stars (NSs), formed via type Ib/c core-collapse supernovae (SNe), which have been spun up to high rotation rates via ...accretion from a companion star in a low-mass X-ray binary (LMXB). In an alternative formation channel, NSs are produced via the accretion-induced collapse (AIC) of a massive white dwarf (WD) in a close binary. Aims. Here we investigate binary evolution leading to AIC and examine if NSs formed in this way can subsequently be recycled to form MSPs and, if so, how they can observationally be distinguished from pulsars formed via the standard core-collapse SN channel in terms of their masses, spins, orbital periods and space velocities. Methods. Numerical calculations with a detailed stellar evolution code were used for the first time to study the combined pre- and post-AIC evolution of close binaries. We investigated the mass transfer onto a massive WD (treated as a point mass) in 240 systems with three different types of non-degenerate donor stars: main-sequence stars, red giants, and helium stars. When the WD is able to accrete sufficient mass (depending on the mass-transfer rate and the duration of the accretion phase) we assumed it collapses to form a NS and we studied the dynamical effects of this implosion on the binary orbit. Subsequently, we followed the mass-transfer epoch which resumes once the donor star refills its Roche lobe and calculated the continued LMXB evolution until the end. Results. We show that recycled pulsars may form via AIC from all three types of progenitor systems investigated and find that the final properties of the resulting MSPs are, in general, remarkably similar to those of MSPs formed via the standard core-collapse SN channel. However, as a consequence of the fine-tuned mass-transfer rate necessary to make the WD grow in mass, the resultant MSPs created via the AIC channel preferentially form in certain orbital period intervals. In addition, their predicted small space velocities can also be used to identify them observationally. The production time of NSs formed via AIC can exceed 10 Gyr which can therefore explain the existence of relatively young NSs in globular clusters. Our calculations are also applicable to progenitor binaries of SNe Ia under certain conditions.
Recent discoveries of weak and fast optical transients raise the question of their origin. We investigate the minimum ejecta mass associated with core-collapse supernovae (SNe) of Type Ic. We show ...that mass transfer from a helium star to a compact companion can produce an ultra-stripped core which undergoes iron core collapse and leads to an extremely fast and faint SN Ic. In this Letter, a detailed example is presented in which the pre-SN stellar mass is barely above the Chandrasekhar limit, resulting in the ejection of only ~0.05-0.20 M sub(middot in circle) of material and the formation of a low-mass neutron star (NS). We compute synthetic light curves of this case and demonstrate that SN 2005ek could be explained by our model. We estimate that the fraction of such ultra-stripped to all SNe could be as high as 10 super(?3)-10 super(?2). Finally, we argue that the second explosion in some double NS systems (for example, the double pulsar PSR J0737?3039B) was likely associated with an ultra-stripped SN Ic.
We present grids of massive star evolution models at four different metallicities ( Z =0.004, 0.002, 0.001, 0.00001). The effects of rotation on the stellar structure and the transport of angular ...momentum and chemical elements through the Spruit-Tayler dynamo and rotationally induced instabilities are considered. After discussing uncertainties involved with the adopted physics, we elaborate the final fate of massive stars as a function of initial mass and spin rate, at each considered metallicity. In particular, we investigate for which initial conditions long gamma-ray bursts (GRBs) are expected to be produced in the frame of the collapsar model. Then, using an empirical spin distribution of young massive metal-poor stars and a specified metallicity-dependent history of star-formation, we compute the expected GRB rate as function of metallicity and redshift based on our stellar evolution models. The GRB production in our models is limited to metallicities of Z \la 0.004, with the consequence that about 50% of all GRBs are predicted to be found at redshifts above z = 4, with most supernovae occurring at redshifts below z\simeq 2.2. The average GRB/SN ratio predicted by our model is about 1/200 globally, and 1/1250 at low redshift. Future strategies for testing the considered GRB progenitor scenario are briefly discussed.
Monte Carlo integration is firmly established as the basis for most practical realistic image synthesis algorithms because of its flexibility and generality. However, the visual quality of rendered ...images often suffers from estimator variance, which appears as visually distracting noise. Adaptive sampling and reconstruction algorithms reduce variance by controlling the sampling density and aggregating samples in a reconstruction step, possibly over large image regions. In this paper we survey recent advances in this area. We distinguish between “a priori” methods that analyze the light transport equations and derive sampling rates and reconstruction filters from this analysis, and “a posteriori” methods that apply statistical techniques to sets of samples to drive the adaptive sampling and reconstruction process. They typically estimate the errors of several reconstruction filters, and select the best filter locally to minimize error. We discuss advantages and disadvantages of recent state‐of‐the‐art techniques, and provide visual and quantitative comparisons. Some of these techniques are proving useful in real‐world applications, and we aim to provide an overview for practitioners and researchers to assess these approaches. In addition, we discuss directions for potential further improvements.
Most massive stars, the progenitors of core-collapse supernovae, are in close binary systems and may interact with their companion through mass transfer or merging. We undertake a population ...synthesis study to compute the delay-time distribution of core-collapse supernovae, that is, the supernova rate versus time following a starburst, taking into account binary interactions. We test the systematic robustness of our results by running various simulations to account for the uncertainties in our standard assumptions. We find that a significant fraction, 15+9-8%, of core-collapse supernovae are “late”, that is, they occur 50–200 Myr after birth, when all massive single stars have already exploded. These late events originate predominantly from binary systems with at least one, or, in most cases, with both stars initially being of intermediate mass (4–8 M⊙). The main evolutionary channels that contribute often involve either the merging of the initially more massive primary star with its companion or the engulfment of the remaining core of the primary by the expanding secondary that has accreted mass at an earlier evolutionary stage. Also, the total number of core-collapse supernovae increases by 14+15-14% because of binarity for the same initial stellar mass. The high rate implies that we should have already observed such late core-collapse supernovae, but have not recognized them as such. We argue that φ Persei is a likely progenitor and that eccentric neutron star – white dwarf systems are likely descendants. Late events can help explain the discrepancy in the delay-time distributions derived from supernova remnants in the Magellanic Clouds and extragalactic type Ia events, lowering the contribution of prompt Ia events. We discuss ways to test these predictions and speculate on the implications for supernova feedback in simulations of galaxy evolution.
In this study, a reduced graphene oxide (rGO)-based nanostructured composite working electrode of high quality was successfully microfabricated and micro-patterned on a flexible polyimide substrate ...using simple low-cost fabrication processes. Gold and platinum alloy nanoparticles were electrochemically deposited onto the microfabricated rGO surface and chitosan-glucose oxidase composites were integrated onto the modified surface of the working electrode to develop a human sweat-based wearable glucose sensor application. The fabricated biosensor exhibited excellent amperometric response to glucose at a detection range of 0–2.4 mM (covers the glucose range in sweat), with a sensitivity of 48 μA/mMcm2, a short response time (20 s), and high linearity (0.99). The detection limit for glucose was calculated as 5 µm. The human sweat/mixing glucose samples initially used for testing indicated acceptable detection performance and stability for low glucose concentrations. These results confirm that the proposed nanostructured composite flexible working electrode and fabrication process are highly promising for application as human sweat-based electrochemical glucose sensors.
•The rGO film was successfully synthesized and micro-patterned on a flexible substrate using a simple low-cost MEMS method.•Gold and platinum alloy nanoparticles (AuPtNP) were electrochemically deposited on the micro-fabricated rGO surface and chitosan-glucose oxidase composites were integrated onto the modified surface of the working electrode to develop a human sweat-based wearable glucose sensor.•The fabricated sensor, comprising three electrodes on a flexible PI substrate, exhibited high sensitivity (45 µA/mMcm2) and favorable detection limits (5 µM glucose) with sweat glucose.
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