Pre-supernova (SN) outbursts from massive stars may be driven by hydrodynamical wave energy emerging from the core of the progenitor star during late nuclear burning phases. Here, we examine the effects of wave heating in stars containing little or no hydrogen, i.e., progenitors of type IIb/Ib SNe. Because there is no massive hydrogen envelope, wave energy is thermalized near the stellar surface where the overlying atmospheric mass is small but the optical depth is large. Wave energy can thus unbind this material, driving an optically thick, super-Eddington wind. Using 1D hydodynamic MESA simulations of ∼ 5 M He stars, we find that wave heating can drive pre-SN outbursts composed of a dense wind whose mass loss rate can exceed ∼ 0.1 M /yr. The wind terminal velocities are a few 100 km/s, and outburst luminosities can reach ∼ 10 6 L . Wave-driven outbursts may be linked with observed or inferred pre-SN outbursts of type Ibn/transitional/transformational SNe, and pre-SN wave-driven mass loss is a good candidate to produce these types of SNe. However, we also show that non-linear wave breaking in the core of the star may prevent such outbursts in stars with thick convective helium-burning shells. Hence, only a limited subset of SN progenitors are likely to experience wave-driven pre-SN outbursts.

The reversible nature of the imine bond formation in CDCl(3) solution has been exploited to exchange substituted for unsubstituted m-phenylenediamine (MPD) units in hemicarcerand octaimines. Moreover, acid-catalyzed imine exchange has been shown to provide a novel mechanism whereby ferrocene (Fc) can be released as an entrapped guest from the hemicarceplex C(2)B(4)&crcldt;Fc dissolved in CDCl(3) to give the hemicarcerand C(2)B(4) when excess of both MPD and trifluoroacetic acid are present.

In a non-spherical stellar explosion, non-radial motions become important near the stellar surface. For realistic deviations from spherical symmetry, non-radial flow dramatically alters the dynamics and emission of shock emergence on a significant fraction of the surface. The breakout flash is stifled, ejecta speeds are limited, and matter is cast sideways. Non-radial ejection allows for collisions outside the star, which may engender a new type of transient. Strongly oblique breakouts are most easily produced in compact stellar progenitors, such as white dwarfs and stripped-envelope core collapse supernovae. We study the shock structure and post-shock acceleration using conservation laws, a similarity analysis, and an approximate theory for oblique shocks. The shock is likely to extend vertically from the stellar surface, then kink before joining a deep asymptotic solution. Outflow from the region crossed by an oblique shock is probably unsteady and may affect the surface ahead of the main shock. We comment on the implications for several notable explosions in which the nonspherical dynamics described in this paper are likely to play an important role. We also briefly consider relativistic and superluminal pattern speeds.

Hydrostatic models of Wolf-Rayet stars typically contain low-density outer envelopes that inflate the stellar radii by a factor of several and are capped by a denser shell of gas. Inflated envelopes and density inversions are hallmarks of envelopes that become super-Eddington as they cross the irongroup opacity peak, but these features disappear when mass loss is sufficiently rapid. We re-examine the structures of steady, spherically symmetric wind solutions that cross a sonic point at high optical depth, identifying the physical mechanism by which outflow affects the stellar structure, and provide an improved analytical estimate for the critical mass loss rate above which extended structures are erased. Weak-flow solutions below this limit resemble hydrostatic stars even in supersonic zones; however, we infer that these fail to successfully launch optically thick winds. Wolf-Rayet envelopes will therefore likely correspond to the strong, compact solutions. We also find that wind solutions with negligible gas pressure are stably stratified at and below the sonic point. This implies that convection is not the source of variability in Wolf-Rayet stars, as has been suggested; but, acoustic instabilities provide an alternative explanation. Our solutions are limited to high optical depths by our neglect of Doppler enhancements to the opacity, and do not account for acoustic instabilities at high Eddington factors; yet they provide useful insights into Wolf-Rayet stellar structures.

We present solutions for the self-similar propagation of a shock wave in a hydrostatic, adiabatic medium with a point mass gravitational field. In contrast to the well-known, Sedov-Taylor blastwave, these solutions apply to the case when the shock Mach number is of order a few, and the energy of the shocked fluid is not conserved but self-consistently modified by the binding energy of the ambient medium that is swept up by the passage of the shock. Furthermore, we show that there is one solution (for a given ambient density profile) that smoothly passes through a sonic point in the post-shock flow and results in accretion onto the central object; in analogy with the Bondi problem, we propose that these solutions are the ones that are most relevant in astrophysical environments. We apply these accreting models to failed supernovae, in which neutron star formation does not unbind the envelope, but a weak shock is still generated in the outer layers of the star from neutrino-induced mass loss. We find excellent agreement between the predictions of our self-similar, shock propagation model and numerical simulations of the collapse of a yellow supergiant; the self-similar solutions reproduce the overall scaling of the shock speed, the time and space-dependent evolution of the velocity, density, and pressure behind the shock, and the accretion rate onto the black hole. Our results have important implications for the fallback and ejection of material in failed supernovae.