We present 2.5-dimensional radiation-hydrodynamics simulations of the accretion-induced collapse (AIC) of white dwarfs, starting from two-dimensional rotational equilibrium configurations, thereby ...accounting consistently for the effects of rotation prior to and after core collapse. We focus our study on a 1.46 and a 1.92 M sub( )a model. Electron capture leads to the collapse to nuclear densities of these cores a few tens of milliseconds after the start of the simulations. The shock generated at bounce moves slowly, but steadily, outward. Within 50-100 ms, the stalled shock breaks out of the white dwarf along the poles. The blast is followed by a neutrino-driven wind that develops within the white dwarf, in a cone of 640 opening angle about the poles, with a mass loss rate of (5-8) x 10 super(-3) M sub( )s super(-1). The ejecta have an entropy on the order of (20-50)k sub(B) baryon super(-1) and an electron fraction that is bimodal. By the end of the simulations, at 600 ms after bounce, the explosion energy has reached (3-4) x 10 super(49) ergs and the mass has reached a few times 10 super(-3) M sub( ). We estimate the asymptotic explosion energies to be lower than 10 super(50) ergs, significantly lower than those inferred for standard core collapse. The AIC of white dwarfs thus represents one instance where a neutrino mechanism leads undoubtedly to a successful, albeit weak, explosion. We document in detail the numerous effects of the fast rotation of the progenitors: the neutron stars are aspherical; the "uk" and super( ) sub(e) neutrino luminosities are reduced compared to the u sub(e) neutrino luminosity; the deleptonized region has a butterfly shape; the neutrino flux and electron fraction depends strongly upon latitude (a la von Zeipel); and aquasi-Keplerian 0.1-0.5 M sub( )accretion disk is formed.
Context. Based mostly on stellar models that do not include rotation, CO white dwarfs that accrete helium at rates of about ~10-8M⊙/ yr have been put forward as candidate progenitors for a number of ...transient astrophysical phenomena, including Type Ia supernovae and the peculiar and fainter Type Iax supernovae. Aims. Here we study the impact of accretion-induced spin-up including the subsequent magnetic field generation, angular momentum transport, and viscous heating on the white dwarf evolution up to the point of helium ignition. Methods. We resolve the structure of the helium accreting white dwarf models with a one-dimensional Langrangian hydrodynamic code, modified to include rotational and magnetic effects, in 315 model sequences adopting different mass-transfer rates (10-8−10-7M⊙/ yr), and initial white dwarf masses (0.54−1.10 M⊙) and luminosities (0.01−1 L⊙). Results. We find magnetic angular momentum transport, which leads to quasi-solid-body rotation, profoundly impacts the evolution of the white dwarf models, and the helium ignition conditions. Our rotating lower mass (0.54 and 0.82 M⊙) models accrete up to 50% more mass up to ignition than the non-rotating case, while it is the opposite for our more massive models. Furthermore, we find that rotation leads to helium ignition densities that are up to ten times smaller, except for the lowest adopted initial white dwarf mass. Ignition densities on the order of 106 g/cm3 are only found for the lowest accretion rates and for large amounts of accreted helium (≳0.4M⊙). However, correspondingly massive donor stars would transfer mass at much higher rates. We therefore expect explosive He-shell burning to mostly occur as deflagrations and at Ṁ > 2 × 10-8M⊙/ yr, regardless of white dwarf mass. Conclusions. Our results imply that helium accretion onto CO white dwarfs at the considered rates is unlikely to lead to the explosion of the CO core or to classical Type Ia supernovae, but may instead produce events that belong to the recently identified classes of faint and fast hydrogen-free supernovae.
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Context. Both recent observations and stellar evolution models suggest that pair-instability supernovae (PISNe) could occur in the local Universe, at metallicities below ≲Z⊙/3. Previous PISN models ...were mostly produced at very low metallicities in the context of the early Universe. Aims. We present new PISNe models at a metallicity of Z = 0.001, which are relevant for the local Universe. Methods. We took previously published self-consistent stellar evolutionary models of pair-instability progenitors with initial masses of 150 M⊙ and 250 M⊙ at metallicity of Z = 0.001 and followed the evolution of these models through the supernova explosions, using a hydrodynamics stellar evolution code with an extensive nuclear network including 200 isotopes. Results. In both models the stars explode as PISNe without leaving a compact stellar remnant. Our models produce a nucleosynthetic pattern that is generally similar to that of Population III PISN models, which is mainly characterized by the production of large amounts of α-elements and a strong deficiency of the odd-charged elements. However, the odd-even effect in our models is significantly weaker than that found in Population III models. The comparison with the nucleosynthetic yields from core-collapse supernovae at a similar metallicity (Z = 0.002) indicates that PISNe could have strongly influenced the chemical evolution below Z ≈ 0.002, assuming a standard initial mass function. The odd-even effect is predicted to be most prominent for the intermediate-mass elements between silicon and calcium. Conclusions. With future observations of chemical abundances in Population II stars, our result can be used to constrain the number of PISNe that occurred during the past evolution of our Galaxy.
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Context. Recently it has been found that models of massive stars reach the Eddington limit in their interior, which leads to dilute extended envelopes. Aims. We perform a comparative study of the ...envelope properties of massive stars at different metallicities, with the aim to establish the impact of the stellar metallicity on the effect of envelope inflation. Methods. We analysed published grids of core-hydrogen burning massive star models computed with metallicities appropriate for massive stars in the Milky Way, the Large Magellanic Cloud, and the Small Magellanic Cloud, the very metal poor dwarf galaxy I Zwicky 18, and for metal-free chemical composition. Results. Stellar models of all the investigated metallicities reach and exceed the Eddington limit in their interior, aided by the opacity peaks of iron, helium, and hydrogen, and consequently develop inflated envelopes. Envelope inflation leads to a redward bending of the zero-age main sequence and a broadening of the main-sequence band in the upper part of the Hertzsprung-Russell diagram. We derive the limiting L/M-values as a function of the stellar surface temperature above which inflation occurs, and find them to be higher for lower metallicity. While Galactic models show inflation above ~29 M⊙, the corresponding mass limit for Population III stars is ~150 M⊙. While the masses of the inflated envelopes are generally low, we find that they can reach 1−100 M⊙ in models with effective temperatures below ~8000 K, with higher masses reached by models of lower metallicity. Conclusions. Envelope inflation is expected to occur in sufficiently massive stars at all metallicities, and is expected to lead to rapidly growing pulsations, high macroturbulent velocities, and might well be related to the unexplained variability observed in luminous blue variables such as S Doradus and η Carina.
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Paleoneuranatomy is an emerging subfield of paleontological research with great potential for the study of evolution. However, the interpretation of fossilized nervous tissues is a difficult task and ...presently lacks a rigorous methodology. We critically review here cases of neural tissue preservation reported in Cambrian arthropods, following a set of fundamental paleontological criteria for their recognition. These criteria are based on a variety of taphonomic parameters and account for morphoanatomical complexity. Application of these criteria shows that firm evidence for fossilized nervous tissues is less abundant and detailed than previously reported, and we synthesize here evidence that has stronger support. We argue that the vascular system, and in particular its lacunae, may be central to the understanding of many of the fossilized peri‐intestinal features known across Cambrian arthropods. In conclusion, our results suggest the need for caution in the interpretation of evidence for fossilized neural tissue, which will increase the accuracy of evolutionary scenarios. Also see the video here: https://youtu.be/2_JlQepRTb0
Burgess‐Shale type fossils have yielded remains of nervous tissues and paved the way for the study of paleoneuroanatomy, but their interpretation has suffered from inconsistent methodology. Based on a critical review of case studies on extinct arthropods, we demonstrate how a thorough understanding of taphonomy and morphoanatomical complexity are essential to an accurate description of fossilized brains.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Context. So-called superluminous supernovae have been recently discovered in the local Universe. It appears possible that some of them originate in stellar explosions induced by the pair instability ...mechanism. Recent stellar evolution models also predict pair instability supernovae from very massive stars at fairly high metallicities (i.e., Z ~ 0.004). Aims. We provide supernova models and synthetic light curves for two progenitor models, a 150 M⊙ red supergiant and a 250 M⊙ yellow supergiant at a metallicity of Z = 0.001, for which the evolution from the main sequence to collapse and the initiation of the pair instability supernova itself has been previously computed in a realistic and self-consistent way. Methods. We use the radiation hydrodynamics code STELLA to describe the supernova evolution of both models in a time frame of about 500 days. Results. We describe the shock-breakout phases of both supernovae, which are characterized by higher luminosity, longer duration, and a lower effective temperature than those of ordinary Type IIP supernovae. We derive the bolometric, as well as the U, B, V, R, and I, light curves of our pair instability supernova models, which show a long-lasting plateau phase with maxima at Mbol ≃ −19.3 mag and −21.3 mag for our lower and higher mass models, respectively. While we do not produce synthetic spectra, we also describe the photospheric composition and velocity as a function of time. Conclusions. We conclude that the light curve of the explosion of our initially 150 M⊙ star resembles those of relatively bright type IIP supernovae, whereas its photospheric velocity at early times is somewhat lower. Its 56Ni mass of 0.04 M⊙ also falls well into the range found in ordinary core collapse supernovae. The light curve and photospheric velocity of our 250 M⊙ models has a striking resemblance to that of the superluminous SN 2007bi, strengthening its interpretation as pair instability supernova. We conclude that pair instability supernovae may occur more frequently in the local universe than previously assumed.
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Context. Type Ia supernovae (SNe Ia) have been an important tool for astronomy for quite some time; however, the nature of their progenitors remains somewhat mysterious. Recent theoretical studies ...indicated the possibility of producing thermonuclear detonations of carbon-oxygen white dwarfs (CO WDs) at masses less than the Chandrasekhar mass through accretion of helium-rich matter, which would, depending on mass accretion rate, mass, and initial temperature of the WD, spectrally resemble either a normal SN Ia or a peculiar one. Aims. This study aims to further resolve the state of binary systems comprised of a sub-Chandrasekhar-mass CO WD and a helium star at the point where an accretion-induced detonation occurs and constrains the part of the initial parameter space where this kind of phenomenon is possible. Methods. Preexisting data obtained through simulations of single, constantly accreting CO WDs is used as an indicator for the behavior of new binary models in which the WD is treated as a point mass and which include the non-degenerate partner as a fully resolved stellar model. We parameterize the ignition of the accumulated helium layer, changes in the WD temperature, and changes in the CO core mass depending on the mass transfer rate. Results. The initial conditions allowing for detonation do not form a single contiguous area in the parameter space, whose shape is profoundly influenced by the behavior of the donor star. Mass loss due to Nova outbursts acts in favor of detonation. According to our criteria, about 10% of the detonations in this study can be expected to show spectra consistent with ordinary SNe Ia; the rest exhibit peculiar features.
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Ni-rich LiNi x Co y Mn1–x–y O2 cathodes (x = 0.6, 0.8, 0.9, and 0.95) were tested to characterize the capacity fading mechanism of extremely rich Ni compositions. Increasing the Ni fraction in the ...cathode delivered a higher discharge capacity (192.9 mA h g–1 for LiNi0.6Co0.2Mn0.2O2 versus 235.0 mA h g–1 for LiNi0.95Co0.025Mn0.025O2); however, the cycling stability was substantially reduced. LiNi0.6Co0.2Mn0.2O2 and LiNi0.8Co0.1Mn0.1O2 retained more than 95% of their respective initial capacities after 100 cycles, while the capacity retention of LiNi0.9Co0.05Mn0.05O2 and LiNi0.95Co0.025Mn0.025O2 was limited to 85% during the same cycling period. The relatively inferior cycling stability of LiNi x Co y Mn1–x–y O2 with x > 0.8 is attributed to the phase transition near the charge-end, causing an abrupt anisotropic shrinkage (or expansion during discharge), which was suppressed for compositions of x < 0.8. Residual stress stemming from the phase transition destabilized the internal microcracks and allowed the microcracks to propagate to the surface, providing channels for electrolyte penetration and subsequent degradation of the exposed internal surfaces formed by the microcracks. Further developments in particle morphology are required to dissipate the intrinsic lattice strain, stabilize the surface, and modify the composition to attain a satisfactory long-term cycling stability, and hence battery life.
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IJS, KILJ, NUK, PNG, UL, UM
Highlights ► LPS hyperalgesia involves activation of microglial/macrophage activity in DRG and spinal cord. ► LPS-induced hyperalgesia is inhibited by minocycline. ► Minocycline suppresses activation ...of microglia/macrophages in DRG and spinal cord but does not affect astrocytes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A recent study indicated that the inner cores of rapidly accreting ($\dot M > 10^{-7}~M_\odot~{\rm yr}^{-1}$) CO white dwarfs may rotate differentially, with a shear rate near the threshold value for ...the onset of the dynamical shear instability. Such differentially rotating white dwarfs have critical masses for thermonuclear explosion or electron-capture induced collapse that significantly exceed the canonical Chandrasekhar limit. Here, we construct two-dimensional differentially rotating white dwarf models with rotation laws resembling those of the one-dimensional models of the previous work. We derive analytic relations between the white dwarf mass, its angular momentum, and its rotational-, gravitational- and binding energy. We show that these relations are applicable for a wide range of angular velocity profiles, including solid body rotation. Taken at a central density of 2 $\times$ $10^9~{\rm g~cm}^{-3}$ they specify initial models for the thermonuclear explosion of rotating CO white dwarfs. At $\rho_{\rm c} = 10^{10}~{\rm g~cm}^{-3}$ and 4 $\times$ $10^{9}~{\rm g~cm}^{-3}$, they give criteria for the electron-capture induced collapse of rotating CO and ONeMg white dwarfs, respectively. We demonstrate that pre-explosion and pre-collapse conditions of both rigidly and differentially rotating white dwarfs are well established by the present work, which may facilitate future multi-dimensional simulations of type Ia supernova explosions and studies of the formation of millisecond pulsars and gamma-ray bursts from collapsing white dwarfs. Our results lead us to suggest various possible evolutionary scenarios for progenitors of type Ia supernovae, leading to a new paradigm of a variable mass of exploding white dwarfs, at values well above the classical Chandrasekhar mass. Based on our 2D-models, we argue that the supernova peak brightness is proportional to the white dwarf mass, which could explain various aspects of the diversity of type Ia supernovae, such as their variation in brightness, the dependence of their mean luminosity on the host galaxy type, and the weak correlation between ejecta velocity and peak brightness.
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