arXiv subjects

Eli Livne

Publications and source records attributed to Eli Livne.

At least 19 recordsLinked to original sources

arXiv2022

Bare Collapse, Formation of Neutron Star Binaries and Fast Optical Transients

{"Bare collapse", the collapse of a bare stellar core to a neutron star with a very small mass ejection links two seemingly unrelated phenomena: the formation of binary neutron star (BNS) systems and the observations of fast and luminous optical transients. We carried out calculations of the collapse due to electron-capture of both evolutionary and synthetic isentropic bare stellar cores. We find that the collapse results in {the formation of} a light ~ 1.3 solar mass neutron star and {an} ejection of ~0.1 solar mass at ~0.1c. The outer shell of the ejecta is composed of Ni56 that can power an ultra-stripped supernova. The models we explored can explain most of the observed fast optical flares but not the brightest ones. Collapse of cores surrounded by somewhat more massive envelopes can produce larger amounts of Ni56 and explain brighter flares. Alternatively, those events can arise due to interaction of the very energetic ejecta with winds that were ejected from the progenitor a few days before the collapse.

astro-ph.HE↗

arXiv2019

Large fluctuations of a Kardar-Parisi-Zhang interface on a half-line: the height statistics at a shifted point

We consider a stochastic interface $h(x,t)$, described by the $1+1$ Kardar-Parisi-Zhang (KPZ) equation on the half-line $x\geq0$ with the reflecting boundary at $x=0$. The interface is initially flat, $h(x,t=0)=0$. We focus on the short-time probability distribution $\mathcal{P}\left(H,L,t\right)$ of the height $H$ of the interface at point $x=L$. Using the optimal fluctuation method, we determine the (Gaussian) body of the distribution and the strongly asymmetric non-Gaussian tails. We find that the slower-decaying tail scales as $-\sqrt{t}\,\ln\mathcal{P}\simeq\left|H\right|^{3/2}f_{-}\left(L/\sqrt{\left|H\right|t}\right)$, and calculate the function $f_{-}(\dots)$ analytically. Remarkably, this tail exhibits a first-order dynamical phase transition at a critical value of $L$, $L_{c}=0.60223\dots\sqrt{\left|H\right|t}$. The transition results from a competition between two different fluctuation paths of the system. The faster decaying tail scales as $-\sqrt{t}\,\ln\mathcal{P}\simeq|H|^{5/2}f_{+}\left(L/\sqrt{|H|t}\right)$. We evaluate the function $f_{+}(\dots)$ using a specially developed numerical method, which involves solving a nonlinear second-order elliptic equation in Lagrangian coordinates. The faster-decaying tail also involves a sharp transition, which occurs at a critical value $L_{c}\simeq2\sqrt{2|H|t}/π$. This transition is similar to the one recently found for the KPZ equation on a ring, and we believe that it has the same fractional order $5/2$. It is smoothed, however, by small diffusion effects.

cond-mat.stat-mech↗

arXiv2018

Ignition of detonation in accreted helium

Sub-Chandrasekhar CO white dwarfs accreting helium have been considered as candidates for Type Ia supernova(SNIa) progenitors since the early 1980s (helium shell mass $> 0.1 M_\odot $). These models, once detonated did not fit the observed spectra and light curve of typical SNIa observations. New theoretical work examined detonations on much less massive ($< 0.05 M_\odot $) envelopes. They find stable detonations that lead to light curves, spectra and abundances that compare relatively well with the observational data. The exact mechanism leading to the ignition of helium detonation is a key issue, since it is a mandatory first step for the whole scenario. As the flow of the accreted envelope is unstable to convection long before any hydrodynamic phenomena develops, a multidimensional approach is needed in order to study the ignition process. The complex convective reactive flow is challenging to any hydrodynamical solver. To the best of our knowledge, all previous 2D studies ignited the detonation artificially. We present here, for the first time, fully consistent results from two hydrodynamical 2D solvers that adopt two independent accurate schemes. For both solvers an effort was made to overcome the problematics raised by the finite resolution and numerical diffusion by the advective terms. Our best models lead to the ignition of a detonation in a convective cell. Our results are robust and the agreement between the two different numerical approaches is very good.

astro-ph.HE↗

arXiv2018

Supernovae from massive stars with extended tenuous envelopes

Massive stars with a core-halo structure are interesting objects for stellar physics and hydrodynamics. Using simulations for stellar evolution, radiation hydrodynamics, and radiative transfer, we study the explosion of stars with an extended and tenuous envelope (i.e., stars in which 95% of the mass is contained within 10% of the surface radius or less). We consider both H-rich supergiant and He-giant progenitors resulting from close-binary evolution and dying with a final mass of 2.8-5Msun. An extended envelope causes the supernova (SN) shock to brake and a reverse shock to form, sweeping core material into a dense shell. The shock deposited energy, which suffers little degradation from expansion, is trapped in ejecta layers of moderate optical depth, thereby enhancing the SN luminosity at early times. With the delayed 56Ni heating, we find that the resulting optical and near-IR light curves all exhibit a double-peak morphology. We show how an extended progenitor can explain the blue and featureless optical spectra of some Type IIb and Ib SNe. The dense shell formed by the reverse shock leads to line profiles with a smaller and near-constant width. This ejecta property can explain the statistically narrower profiles of Type IIb compared to Type Ib SNe, as well as the peculiar Halpha profile seen in SN1993J. At early times, our He-giant star explosion model shows a high luminosity, a blue color, and featureless spectra reminiscent of the Type Ib SN2008D, suggesting a low-mass progenitor.

astro-ph.HE↗

arXiv2017

Progenitors of low-luminosity Type II-Plateau supernovae

The progenitors of low-luminosity Type II-Plateau supernovae (SNe II-P) are believed to be red supergiant (RSG) stars, but there is much disparity in the literature concerning their mass at core collapse and therefore on the main sequence. Here, we model the SN radiation arising from the low-energy explosion of RSG stars of 12, 25, and 27 M$_{\odot}$ on the main sequence and formed through single star evolution. Despite the narrow range in ejecta kinetic energy (2.5$-$4.2$\times$10$^{50}$ erg) in our model set, the SN observables from our three models are significantly distinct, reflecting the differences in progenitor structure (e.g., surface radius, H-rich envelope mass, He-core mass). Our higher mass RSG stars give rise to Type II SNe that tend to have bluer colors at early times, a shorter photospheric phase, and a faster declining $V$-band light curve (LC) more typical of Type II-linear SNe, in conflict with the LC plateau observed for low-luminosity SNe II. The complete fallback of the CO core in the low-energy explosions of our high mass RSG stars prevents the ejection of any ${}^{56}$Ni (nor any core O or Si), in contrast to low-luminosity SNe II-P, which eject at least 0.001 M$_{\odot}$ of ${}^{56}$Ni. In contrast to observations, type II SN models from higher mass RSGs tend to show an H$α$ absorption that remains broad at late times (due to a larger velocity at the base of the H-rich envelope). In agreement with the analyses of pre-explosion photometry, we conclude that low-luminosity SNe II-P likely arise from low-mass rather than high-mass RSG stars.

astro-ph.HE↗

arXiv2017

Radiative-transfer models for explosions from rotating and non-rotating single WC stars. Implications for SN1998bw and LGRB/SNe

Using 1-D non-Local-Thermodynamic-Equilibrium time-dependent radiative-transfer simulations, we study the ejecta properties required to match the early and late-time photometric and spectroscopic properties of supernovae (SNe) associated with long-duration gamma-ray bursts (LGRBs). To match the short rise time, narrow light curve peak, and extremely broad spectral lines of SN1998bw requires a model with <3Msun ejecta but a high explosion energy of a few 1e52erg and 0.5Msun of Ni56. However the relatively high luminosity, the presence of narrow spectral lines of intermediate mass elements, and the low ionization at the nebular stage are matched with a more standard C-rich Wolf-Rayet (WR) star explosion, with an ejecta of >10Msun, an explosion energy >1e51erg, and only 0.1Msun of Ni56. As the two models are mutually exclusive, the breaking of spherical symmetry is essential to match the early/late photometric/spectroscopic properties of SN1998bw. This conclusion confirms the notion that the ejecta of SN1998bw is aspherical on large scales. More generally, with asphericity, the energetics and Ni56 mass of LGRB/SNe are reduced and their ejecta mass is increased, favoring a massive fast-rotating Wolf-Rayet star progenitor. Contrary to persisting claims in favor of the proto-magnetar model for LGRB/SNe, such progenitor/ejecta properties are compatible with collapsar formation. Ejecta properties of LGRB/SNe inferred from 1D radiative-transfer modeling are fundamentally flawed.

astro-ph.SR↗

arXiv2016

A study of the low-luminosity Type II-Plateau supernova 2008bk

Supernova (SN) 2008bk is a well observed low-luminosity Type II event visually associated with a low-mass red-supergiant progenitor. To model SN 2008bk, we evolve a 12Msun star from the main sequence until core collapse, when it has a total mass of 9.88Msun, a He-core mass of 3.22Msun, and a radius of 502Rsun. We then artificially trigger an explosion that produces 8.29Msun of ejecta with a total energy of 2.5x10^50erg and ~0.009Msun of 56Ni. We model the subsequent evolution of the ejecta with non-Local-Thermodynamic-Equilibrium time-dependent radiative transfer. Although somewhat too luminous and energetic, this model reproduces satisfactorily the multi-band light curves and multi-epoch spectra of SN 2008bk, confirming the suitability of a low-mass massive star progenitor. As in other low-luminosity SNe II, the structured Halpha profile at the end of the plateau phase is probably caused by BaII 6496.9A rather than asphericity. We discuss the sensitivity of our results to changes in progenitor radius and mass, as well as chemical mixing. A 15% increase in progenitor radius causes a 15% increase in luminosity and a 0.2mag V-band brightening of the plateau but leaves its length unaffected. An increase in ejecta mass by 10% lengthens the plateau by ~10d. Chemical mixing introduces slight changes to the bolometric light curve, limited to the end of the plateau, but has a large impact on colours and spectra at nebular times.

astro-ph.SR↗

arXiv2016

Inferring supernova IIb/Ib/Ic ejecta properties from light curves and spectra: Correlations from radiative-transfer models

We present 1-D non-Local-Thermodynamic-Equilibrium time-dependent radiative-transfer simulations for a large grid of supernovae (SNe) IIb/Ib/Ic that result from the terminal explosion of the mass donor in a close-binary system. Our sample covers ejecta masses $M_{\rm e}$ of 1.7$-$5.2M$_\odot$, kinetic energies $E_{\rm kin}$ of 0.6$-$5.0$\times$10$^{51}$erg, and $^{56}$Ni masses of 0.05$-$0.30M$_\odot$. We find a strong correlation between the $^{56}$Ni mass and the photometric properties at maximum, and between the rise time to bolometric maximum and the post-maximum decline rate. We confirm the small scatter in ($V-R$) at 10d past $R$-band maximum. The quantity $V_{\rm m} \equiv \sqrt{2E_{\rm kin}/M_{\rm e}}$ is comparable to the Doppler velocity measured from HeI 5875Å at maximum in SNe IIb/Ib, although some scatter arises from the uncertain level of chemical mixing. The OI7772Å line may be used for SNe Ic, but the correspondence deteriorates with higher ejecta mass/energy. We identify a temporal reversal of the Doppler velocity at maximum absorption in the $\sim$1.05$μ$m feature in all models. The reversal is due to HeI alone and could serve as a test for the presence of helium in SNe Ic. Because of variations in composition and ionisation, the ejecta opacity shows substantial variations with both velocity and time. This is in part the origin of the offset between our model light curves and the predictions from the Arnett model.

astro-ph.SR↗

arXiv2016

Models of interacting supernovae and their spectral diversity

Using radiation-hydrodynamics and radiative-transfer simulations, we explore the origin of the spectral diversity of interacting supernovae (SNe) of type IIn. We revisit SN1994W and investigate the dynamical configurations that can give rise to spectra with narrow lines at all times. We find that a standard ~10Msun 10^51erg SN ejecta ramming into a 0.4Msun dense CSM is inadequate for SN1994W, as it leads to the appearance of broad lines at late times. This structure, however, generates spectra that exhibit the key morphological changes seen in SN1998S. For SN1994W, we consider a completely different configuration, which involves the interaction at a large radius of a low mass inner shell with a high mass outer shell. Such a structure may arise in an 8-12Msun star from a nuclear flash (e.g., of Ne) followed within a few years by core collapse. Our simulations show that the large mass of the outer shell leads to the complete braking of the inner shell material, the formation of a slow dense shell, and the powering of a luminous SN IIn, even for a low inner shell energy. Early on, our model line profiles are typical of SNe IIn, exhibiting narrow cores and broad electron-scattering wings. As observed in SN1994W, they also remain narrow at late times. Our SN1994W model invokes two low energy ejections, both atypical of observed massive stars, and illustrates the diversity of configurations leading to SNe IIn. These results also highlight the importance of spectra to constrain the dynamical properties and understand the origin of SNe IIn.

astro-ph.SR↗

arXiv2015

Radiative-transfer models for supernovae IIb/Ib/Ic from binary-star progenitors

We present 1-D non-Local-Thermodynamic-Equilibrium time-dependent radiative-transfer simulations for supernovae (SNe) of type IIb, Ib, and Ic that result from the terminal explosion of the mass donor in a close-binary system. Here, we select three ejecta with a total kinetic energy of ~1.2e51erg, but characterised by different ejecta masses (2-5Msun), composition, and chemical mixing. The type IIb/Ib models correspond to the progenitors that have retained their He-rich shell at the time of explosion. The type Ic model arises from a progenitor that has lost its helium shell, but retains 0.32Msun of helium in a CO-rich core of 5.11Msun. We discuss their photometric and spectroscopic properties during the first 2-3 months after explosion, and connect these to their progenitor and ejecta properties including chemical stratification. For these three models, Arnett's rule overestimates the 56Ni mass by ~50% while the procedure of Katz et al., based on an energy argument, yields a more reliable estimate. The presence of strong CI lines around 9000A prior to maximum is an indicator that the pre-SN star was under-abundant in helium. As noted by others, the 1.08micron feature is a complex blend of CI, MgII, and HeI lines, which makes the identification of He uncertain in SNe Ibc unless other HeI lines can be identified. Our models show little scatter in (V-R) colour 10d after R-band maximum. We also address a number of radiative transfer properties of SNe Ibc, including the notion of a photosphere, the inference of a representative ejecta expansion rate, spectrum formation, blackbody fits and "correction factors".

astro-ph.SR↗

arXiv2013

Head-on collisions of white dwarfs in triple systems could explain type Ia supernova

Type Ia supernovae (SNe Ia), thermonuclear explosions of carbon-oxygen white dwarfs (CO-WDs), are currently the best cosmological "standard candles", but the triggering mechanism of the explosion is unknown. It was recently shown that the rate of head-on collisions of typical field CO-WDs in triple systems may be comparable to the SNe Ia rate. Here we provide evidence supporting a scenario in which the majority of SNe Ia are the result of such head-on collisions of CO-WDs. In this case, the nuclear detonation is due to a well understood shock ignition, devoid of commonly introduced free parameters such as the deflagration velocity or transition to detonation criteria. By using two-dimensional hydrodynamical simulations with a fully resolved ignition process, we show that zero-impact-parameter collisions of typical CO-WDs with masses $0.5-1\,M_{\odot}$ result in explosions that synthesize $^{56}$Ni masses in the range of $\sim0.1-1\,M_{\odot}$, spanning the wide distribution of yields observed for the majority of SNe Ia. All collision models yield the same late-time ($>60$ days since explosion) bolometric light curve when normalized by $^{56}$Ni masses (to better than $30\%$), in agreement with observations. The calculated widths of the $^{56}$Ni-mass-weighted-line-of-sight velocity distributions are correlated with the calculated $^{56}$Ni yield, agreeing with the observed correlation. The strong correlation, shown here for the first time, between $^{56}$Ni yield and total mass of the colliding CO-WDs (insensitive to their mass ratio), is suggestive as the source for the continuous distribution of observed SN Ia features, possibly including the Philips relation.

astro-ph.HE↗

arXiv2013

Type II-Plateau supernova radiation: dependencies on progenitor and explosion properties

We explore the properties of Type II-Plateau (II-P) supernovae (SNe) together with their red-supergiant (RSG) star progenitors. Using MESA STAR, we modulate the parameters (e.g., mixing length, overshoot, rotation, metallicity) that control the evolution of a 15Msun main-sequence star to produce a variety of physical pre-SN models and SN II-P ejecta. We extend previous modeling of SN II-P radiation to include photospheric and nebular phases, as well as multi-band light curves and spectra. Our treatment does not assume local thermodynamic equilibrium, is time dependent, treats explicitly the effects of line blanketing, and incorporates non-thermal processes. We find that the color properties of SNe II-P require large model atoms for FeI and FeII, much larger than adopted in Dessart & Hillier (2011). The color properties also imply RSG progenitors of limited extent (~500Rsun) --- larger progenitor stars produce a SN II-P radiation that remains too blue for too long. This finding calls for a reduction of RSG radii, perhaps through a strengthening of convective energy transport in RSG envelopes. Increased overshoot and rotation reduce the ratio of ejecta to helium-core mass, similarly to an increase in main-sequence mass, and thus complicate the inference ofprogenitor masses. In contrast to the great sensitivity on progenitor radius, SN II-P color evolution appears insensitive to variations in explosion energy. Finally, we document the numerous SN II-P signatures that vary with progenitor metallicity, revealing their potential for metallicity determinations in the nearby and distant Universe.

astro-ph.SR↗

arXiv2012

Radiative Properties of Pair-instability Supernova Explosions

We present non-LTE time-dependent radiative-transfer simulations of pair-instability supernovae (PISNe) stemming from red-supergiant (RSG), blue-supergiant (BSG) and Wolf-Rayet (WR) star rotation-free progenitors born in the mass range 160-230Msun, at 10^-4 Zsun. Although subject to uncertainties in convection and stellar mass-loss rates, our initial conditions come from physically-consistent models that treat evolution from the main-sequence, the onset of the pair-production instability, and the explosion phase. With our set of input models characterized by large 56Ni and ejecta masses, and large kinetic energies, we recover qualitatively the Type II-Plateau, II-peculiar, and Ib/c light-curve morphologies, although they have larger peak bolometric luminosities (~10^9 to 10^10 Lsun) and a longer duration (~200d). We discuss the spectral properties for each model during the photospheric and nebular phases, including Balmer lines in II-P and II-pec at early times, the dominance of lines from intermediate-mass-elements (IMEs) near the bolometric maximum, and the strengthening of metal line blanketing thereafter. Having similar He-core properties, all models exhibit similar post-peak spectra that are strongly blanketed by FeII and FeI lines, characterized by red colors, and that arise from photospheres/ejecta with a temperature of <4000K. Combined with the modest line widths after bolometric peak, these properties contrast with those of known super-luminous SNe suggesting that PISNe are yet to be discovered. Being reddish, PISNe will be difficult to observe at high redshift except when they stem from RSG explosions, in which case they could be used as metallicity probes and distance indicators.

astro-ph.SR↗

arXiv2012

Convective overshoot mixing in Nova outbursts - The dependence on the composition of the underlying white dwarf

We present here, for the first time, a 2D study of the overshoot convective mechanism in nova outbursts for a wide range of possible compositions of the layer underlying the accreted envelope. Previous surveys studied this mechanism only for solar composition matter accreted on top of carbon oxygen (C-O) white dwarfs. Since, during the runaway, mixing with carbon enhances the hydrogen burning rates dramatically, one should question whether significant enrichment of the ejecta is possible also for other underlying compositions (He, O, Ne, Mg), predicted by stellar evolution models. We simulated several non-carbon cases and found significant amounts of those underlying materials in the ejected hydrogen layer. Despite large differences in rates, time scales and energetics between the cases, our results show that the convective dredge up mechanism predicts significant enrichment in all our non-carbon cases, including helium enrichment in recurrent novae. The results are consistent with observations.

astro-ph.SR↗

arXiv2012

Super-luminous supernovae: 56Ni power versus magnetar radiation

Much uncertainty surrounds the origin of super-luminous supernovae (SNe). Motivated by the discovery of the Type Ic SN2007bi, we study its proposed association with a pair-instability SN (PISN). We compute stellar-evolution models for primordial ~200Msun stars, simulating the implosion/explosion due to the pair-production instability, and use them as inputs for detailed non-LTE time-dependent radiative-transfer simulations that include non-local energy deposition and non-thermal processes. We retrieve the basic morphology of PISN light curves from red-supergiant, blue-supergiant, and Wolf-Rayet (WR) star progenitors. Although we confirm that a progenitor 100Msun helium core (PISN model He100) fits well the SN2007bi light curve, the low ratios of its kinetic energy and 56Ni mass to the ejecta mass, similar to standard core-collapse SNe, conspire to produce cool photospheres, red spectra subject to strong line blanketing, and narrow line profiles, all conflicting with SN2007bi observations. He-core models of increasing 56Ni-to-ejecta mass ratio have bluer spectra, but still too red to match SN2007bi, even for model He125 -- the effect of 56Ni heating is offset by the associated increase in blanketing. In contrast, the delayed injection of energy by a magnetar represents a more attractive alternative to reproduce the blue, weakly-blanketed, and broad-lined spectra of super-luminous SNe. The extra heat source is free of blanketing and is not explicitly tied to the ejecta. Experimenting with a ~9Msun WR-star progenitor, initially exploded to yield a ~1.6B SN Ib/c ejecta but later influenced by tunable magnetar-like radiation, we produce a diversity of blue spectral morphologies reminiscent of SN2007bi, the peculiar Type Ib SN2005bf, and super-luminous SN2005ap-like events.

astro-ph.SR↗

arXiv2012

Imploding ignition waves: I. one dimensional analysis

We show that converging spherical and cylindrical shock waves may ignite a detonation wave in a combustible medium, provided the radius at which the shocks become strong exceeds a critical radius, R_c. An approximate analytic expression for R_c is derived for an ideal gas equation of state and a simple (power-law-Arrhenius) reaction law, and shown to reproduce the results of numerical solutions. For typical acetylene-air experiments we find R_c~0.1 mm (spherical) and R_c~1 mm (cylindrical). We suggest that the deflagration to detonation transition (DDT) observed in these systems may be due to converging shocks produced by the turbulent deflagration flow, which reaches sub (but near) sonic velocities on scales >>R_c. Our suggested mechanism differs from that proposed by Zel'dovich et al., in which a fine-tuned spatial gradient in the chemical induction time is required to be maintained within the turbulent deflagration flow. Our analysis may be readily extended to more complicated equations of state and reaction laws. An order of magnitude estimate of R_c within a white dwarf at the pre-detonation conditions believed to lead to Type Ia supernova explosions is 0.1 km, suggesting that our proposed mechanism may be relevant for DDT initiation in these systems. The relevance of our proposed ignition mechanism to DDT initiation may be tested by both experiments and numerical simulations.

astro-ph.HE↗

arXiv2011

Early emission from type Ia supernovae

A unique feature of deflagration-to-detonation (DDT) white dwarf explosion models of SNe of type Ia is the presence of a strong shock wave propagating through the outer envelope. We consider the early emission expected in such models, which is produced by the expanding shock-heated outer part of the ejecta and precedes the emission driven by radioactive decay. We expand on earlier analyses by considering the modification of the pre-detonation density profile by the weak-shocks generated during the deflagration phase, the time evolution of the opacity, and the deviation of the post-shock equation of state from that obtained for radiation pressure domination. A simple analytic model is presented and shown to provide an acceptable approximation to the results of 1D numerical DDT simulations. Our analysis predicts a thousand second long UV/optical flash with a luminosity of ~1 to 3*1e39 erg/s. Lower luminosity corresponds to faster (turbulent) deflagration velocity. The predicted luminosity of the UV flash is an order of magnitude lower than that of earlier estimates, and is expected to be strongly suppressed at times longer than an hour due to the deviation from pure radiation domination.

astro-ph.HE↗

arXiv2011

Core-collapse explosions of Wolf-Rayet stars and the connection to type IIb/Ib/Ic supernovae

We present non-LTE time-dependent radiative-transfer simulations of supernova (SN) IIb/Ib/Ic spectra and light curves, based on ~1B-energy piston-driven ejecta, with and without 56Ni, produced from single and binary Wolf-Rayet (W-R) stars evolved at solar and sub-solar metallicities. Our bolometric light curves show a 10-day long post-breakout plateau with a luminosity of 1-5x10^7Lsun. In our 56Ni-rich models, with ~3Msun ejecta masses, this plateau precedes a 20-30-day long re-brightening phase initiated by the outward-diffusing heat wave powered by radioactive decay at depth. In low ejecta-mass models with moderate mixing, Gamma-ray leakage starts as early as ~50d after explosion and causes the nebular luminosity to steeply decline by ~0.02mag/d. Such signatures, which are observed in standard SNe IIb/Ib/Ic, are consistent with low-mass progenitors derived from a binary-star population. We propose that the majority of stars with an initial mass ~<20Msun yield SNe II-P if 'effectively" single, SNe IIb/Ib/Ic if part of a close binary system, and SN-less black holes if more massive. Our ejecta, with outer hydrogen mass fractions as low as ~>0.01 and a total hydrogen mass of ~>0.001Msun, yield the characteristic SN IIb spectral morphology at early times. However, by ~15d after the explosion, only Halpha may remain as a weak absorption feature. Our binary models, characterised by helium surface mass fractions of ~>0.85, systematically show HeI lines during the post-breakout plateau, irrespective of the 56Ni abundance. Synthetic spectra show a strong sensitivity to metallicity, which offers the possibility to constrain it directly from SN spectroscopic modelling.

astro-ph.SR↗