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Register a new userThe diversity of supernovae and impostors shortly after explosion
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Observational surveys are now able to detect an increasing number of transients, such as core-collapse supernovae (SN) and powerful non-terminal outbursts (SN impostors). Dedicated spectroscopic facilities can follow up these events shortly after detection. Here we investigate the properties of these explosions at early times. We use the radiative transfer code CMFGEN to build an extensive library of spectra simulating the interaction of supernovae and their progenitors winds/circumstellar medium (CSM). We consider a range of progenitor mass-loss rates (Mdot = 5e-4 to 1e-2 Msun/yr), abundances (solar, CNO-processed, and He-rich), and SN luminosities (L = 1.9e8 to 2.5e10 Lsun). The models simulate events ~1 day after explosion, and we assume a fixed location of the shock front as Rin=8.6e13 cm. We show that the large range of massive star properties at the pre-SN stage causes a diversity of early-time interacting SN and impostors. We identify three main classes of early-time spectra consisting of relatively high-ionisation (e.g. Ovi), medium-ionisation (e.g. Ciii), and low-ionisation lines (e.g. Feii/iii). They are regulated by L and the CSM density. Given a progenitor wind velocity Vinf, our models also place a lower limit of Mdot > 5e-4 (Vinf/150 km/s) Msun/yr for detection of CSM interaction signatures in observed spectra. Early-time SN spectra should provide clear constraints on progenitors by measuring H, He, and CNO abundances if the progenitors come from single stars. The connections are less clear considering the effects of binary evolution. Yet, our models provide a clear path for linking the final stages of massive stars to their post-explosion spectra at early times, and guiding future observational follow-up of transients with facilities such as the Zwicky Transient Facility.
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We present a set of nonlocal thermodynamic equilibrium steady-state calculations of radiative transfer for one-year old type II supernovae (SNe) starting from state-of-the-art explosion models computed with detailed nucleosynthesis. This grid covers single-star progenitors with initial masses between 9 and 29$M_{odot}$, all evolved with KEPLER at solar metallicity and ignoring rotation. The [OI]$lambdalambda$$6300,6364$ line flux generally grows with progenitor mass, and H$alpha$ exhibits an equally strong and opposite trend. The [CaII]$lambdalambda$$7291,,7323$ strength increases at low $^{56}$Ni mass, low explosion energy, or with clumping. This CaII doublet, which forms primarily in the explosively-produced Si/S zones, depends little on the progenitor mass, but may strengthen if Ca$^+$ dominates in the H-rich emitting zones or if Ca is abundant in the O-rich zones. Indeed, Si-O shell merging prior to core collapse may boost the CaII doublet at the expense of the OI doublet, and may thus mimic the metal line strengths of a lower mass progenitor. We find that the $^{56}$Ni bubble effect has a weak impact, probably because it is too weak to induce much of an ionization shift in the various emitting zones. Our simulations compare favorably to observed SNe II, including SN2008bk (e.g., 9$M_{odot}$ model), SN2012aw (12$M_{odot}$ model), SN1987A (15$M_{odot}$ model), or SN2015bs (25$M_{odot}$ model with no Si-O shell merging). SNe II with narrow lines and a low $^{56}$Ni mass are well matched by the weak explosion of 9$-$11$M_{odot}$ progenitors. The nebular-phase spectra of standard SNe II can be explained with progenitors in the mass range 12$-$15$M_{odot}$, with one notable exception for SN2015bs. In the intermediate mass range, these mass estimates may increase by a few $M_{odot}$ with allowance for clumping of the O-rich material or CO molecular cooling.
Supernovae explosions of massive stars are nowadays believed to result from a two-step process, with an initial gravitational core collapse followed by an expansion of matter after a bouncing on the core. This scenario meets several difficulties. We show that it is not the only possible one: a simple model based on fluid mechanics and stability properties of the equilibrium state shows that one can have also a simultaneous inward/outward motion in the early stage of the instability of the supernova. This shows up in the slow sweeping across a saddle-center bifurcation found when considering equilibrium states associated to the constraint of energy conservation. We first discuss the weakly nonlinear regime in terms of a Painleve I equation. We then show that the strongly nonlinear regime displays a self-similar behavior of the core collapse. Finally, the expansion of the remnants is revisited as an isentropic process leading to shocks formation.
Much difficulty has so far prevented the emergence of a consistent scenario for the origin of Type Ib and Ic supernovae (SNe). Here, we follow a heuristic approach by examining the fate of helium stars in the mass range 4 to 12Msun, which presumably form in interacting binaries. The helium stars are evolved using stellar wind mass loss rates that agree with observations, and which reproduce the observed luminosity range of galactic WR stars, leading to stellar masses at core collapse in the range 3-5.5Msun. We then explode these models adopting an explosion energy proportional to the ejecta mass, roughly consistent with theoretical predictions. We impose a fixed 56Ni mass and strong mixing. The SN radiation from 3 to 100d is computed self-consistently starting from the input stellar models using the time-dependent non-local thermodynamic equilibrium radiative-transfer code CMFGEN. By design, our fiducial models yield similar light curves, with a rise time of ~20d and a peak luminosity of ~10^42.2erg/s, in line with representative SNe Ibc. The less massive progenitors retain a He-rich envelope and reproduce the color, line widths, and line strengths of a representative sample of SNe Ib, while stellar winds remove most of the helium in more massive progenitors, whose spectra match typical SNe Ic in detail. The transition between the predicted Ib-like and Ic-like spectra is continuous, but it is sharp, such that the resulting models essentially form a dichotomy. Further models computed with varying explosion energy, 56Ni mass, and long-term power injection from the remnant show that a moderate variation of these parameters can reproduce much of the diversity of SNe Ibc. We conclude that stars stripped by a binary companion can account for the vast majority of ordinary SNe Ib and Ic, and that stellar wind mass loss is the key to remove the helium envelope in SN Ic progenitors. [abridged]
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We consider a model of the early universe which consists of two scalar fields: the inflaton, and a second field which drives the stabilisation of the Planck mass (or gravitational constant). We show that the non-minimal coupling of this second field to the Ricci scalar sources a non-adiabatic pressure perturbation. By performing a fully numerical calculation we find, in turn, that this boosts the amplitude of the primordial power spectrum after inflation.
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