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In the version of this Letter originally published, the caption of Fig. 2 incorrectly said J = 3–2; it should have said J = 2–1. This has now been corrected.

The progenitors of many CCSNe are expected to be in binary systems. After the SN explosion, the companion may suffer from mass stripping and be shock heated as a result of the impact of the SN ejecta. If the binary system is disrupted, the companion is ejected as a runaway and hypervelocity star. By performing a series of 3D hydrodynamical simulations of the collision of SN ejecta with the companion star, we investigate how CCSN explosions affect their companions. We use the BEC code to construct the detailed companion structure at the time of SN explosion. The impact of the SN blast wave on the companion is followed by means of 3D SPH simulations using the Stellar GADGET code. For main-sequence (MS) companions, we find that the amount of removed mass, impact velocity, and chemical contamination of the companion that results from the impact of the SN ejecta, strongly increases with decreasing binary separation and increasing explosion energy. Their relationship can be approximately fitted by power laws, which is consistent with the results obtained from impact simulations of SNe~Ia. However, we find that the impact velocity is sensitive to the momentum profile of the outer SN ejecta and, in fact, may decrease with increasing ejecta mass, depending on the modeling of the ejecta. Because most companions to Ib/c CCSNe are in their MS phase at the moment of the explosion, combined with the strongly decaying impact effects with increasing binary separation, we argue that the majority of these SNe lead to inefficient mass stripping and shock heating of the companion star following the impact of the ejecta. Our simulations show that the impact effects of Ib/c SN ejecta on the structure of MS companions, and thus their long-term post-explosion evolution, is in general not dramatic. We find that at most 10% of their mass is lost, and their resulting impact velocities are less than 100 km/s., Comment: Accepted for publication in Astronomy and Astrophysics, some minor typographical errors are fixed, the affiliation of second author is corrected

We present models for the slow neutron-capture process (s-process) in asymptotic giant branch stars of metallicity [Fe/H] = −2.3 and masses 0.9 – 6M⊙. The models where the 13C burns radiatively (stars of around 2M⊙) produce an overall good match to carbon-enhanced metalpoor (CEMP) stars showing barium enhancements (CEMP-s). On the other hand, none of our models can provide a match to the composition of CEMP stars showing both barium and europium enhancements (CEMP-s/r). The models fail to reproduce the observed Eu abundances, and they also fail to reproduce the correlation between the Eu and Ba abundances. They also cannot match the ratio of heavy-to-light s-process elements observed in many CEMP-s/r stars, which can be more than 10 times higher than in the Solar System. This work has been published [1] and the interested reader should refer to that work for further details, included published tables of yields.

We have performed calculations for the slow neutron capture process (the s process) in stellar models of mass from 0.9 M⊙ to 6 M⊙ at a metallicity of [Fe/H] = −2.3. The models were computed with two different stellar evolution codes and our results compared to the composition of the elements heavier than Fe observed in carbon-enhanced metal-poor (CEMP) stars. Our models provide an explanation for the compositions of CEMP stars showing s-process signature (CEMP-s) but not for the composition of CEMP stars showing both s-process and rapid neutron-capture (r-process) signature (CEMP-s/r). To explain the composition of CEMP-s/r we propose the existence of a “s/r” neutron-capture process, which may be a superposition of, or a process in-between, the classical s and r processes. Here we attempt at understanding some qualitative features of the s/r process on the basis of the observational constraints.