Wolf-Rayet stars and their nucleosynthetic signatures in meteorites

Wolf-Rayet (WR) stars are fascinating objects that have a dramatic impact on their surroundings. Their many facets have been, and still are, the focus of much observational and theoretical efforts by a large community of astrophysicists. It is scientifically sound to examine if, in addition, they could also be of special interest in the exciting chapter of cosmochemistry dealing with isotopic anomalies found in a variety of meteoritic materials. After a brief review of some important observed features of WR stars, as well as of the commonly accepted theoretical interpretation of these observed characteristics, this contribution addresses two questions: (1) could WR stars have been the sources of presolar grains that have been preserved up to now in meteorites, and (2) could WR stars have injected into forming solar system solids some isotopically anomalous freshly produced material, and in particular short-lived radionuclides? On grounds of detailed WR models, we answer the first question by saying that no clear and unambiguous signature of the existence in meteorites of presolar grains of WR origin has been identified to date in the laboratory. Further discoveries might of course impose a modification of this statement. The second question, i. e. the injection of freshly produced material into the forming solar system, is obviously a very complex one. It is concluded that a series of radionuclides (e.g. ${}^{26}\mathrm{Al},$ ${}^{36}\mathrm{Cl},$ ${}^{41}\mathrm{Ca},$ ${}^{107}\mathrm{Pd}$ ) could be produced by a variety of non-exploding WR stars at relative levels compatible with the meteoritic observations. The eventual supernova explosion of the considered stars could produce its complementary share of radionuclides of interest. This nucleosynthesis is a necessary, but not sufficient, condition for the contamination of the forming solar system. We complement this condition with the contention, based on qualitative considerations, that astrophysically plausible situations might exist such that radionuclides ejected by WR stars could contaminate the solar system at absolute levels requested by the observations. Of course, the interaction of WR stars with their surroundings is of extreme complexity. These complications should clearly have to be considered in order to reject or confirm the qualitative conclusion that WR stars could indeed be viable “last minute” solar system contaminators.