Short‐lived radioactivity in the early solar system: The Super‐AGB star hypothesis

Abstract

Abstract-The composition of the most primitive solar system condensates, such as calciumaluminum-rich inclusions (CAIs) and micron-sized corundum grains, show that short-lived radionuclides (SLR), e.g., 26 Al, were present in the early solar system. Their abundances require a local or stellar origin, which, however, is far from being understood. We present for the first time the abundances of several SLR up to 60 Fe predicted from stars with initial mass in the range approximately 7-11 M x . These stars evolve through core H, He, and C burning. After core C burning they go through a ''Super''-asymptotic giant branch (Super-AGB) phase, with the H and He shells activated alternately, episodic thermal pulses in the He shell, a very hot temperature at the base of the convective envelope (approximately 10 8 K), and strong stellar winds driving the H-rich envelope into the surrounding interstellar medium. The final remnants of the evolution of Super-AGB stars are mostly O-Ne white dwarfs. Our Super-AGB models produce 26 Al ⁄ 27 Al yield ratios approximately 0.02-0.26. These models can account for the canonical value of the 26 Al ⁄ 27Al ratio using dilutions with the solar nebula of the order of 1 part of Super-AGB mass per several 10 2 to several 10 3 of solar nebula mass, resulting in associated changes in the O-isotope composition in the range D 17 O from 3 to 20&. This is in agreement with observations of the O isotopic ratios in primitive solar system condensates, which do not carry the signature of a stellar polluter. The radionuclides 41 Ca and 60 Fe are produced by neutron captures in Super-AGB stars and their meteoritic abundances are also matched by some of our models, depending on the nuclear and stellar physics uncertainties as well as the meteoritic experimental data. We also expect and are currently investigating Super-AGB production of SLR heavier than iron, such as 107 Pd.

Super- and massive AGB stars – IV. Final fates – initial-to-final mass relation

“…Different metallicities and larger grids of super-AGB models have started to populate the literature more recently (e.g. Siess 2006;Gil-Pons et al 2007;Poelarends et al 2008;Doherty et al 2010;Siess 2010;Ventura & D'Antona 2010;Lugaro et al 2012;Karakas et al 2012;Herwig et al 2012;Gil-Pons et al 2013;Ventura et al 2013;Jones et al 2013).…”

Probing astrophysically important states in theMg26nucleus to study neutron sources for thesprocess

“…At low metallicity the elemnetal products of the sprocess nucleosynthesis in AGB stars can be directly observed in carbon-enhanced metal poor stars [4], [14], [15], [16], in post-AGB stars [17], [18] and in Ba stars [19]. For several cases the observations seem to agree well with theoretical model predictions [20], [21], while for other cases there are problems to reproduce the observations [22], [?…”

Numerical studies on the link between radioisotopic signatures on Earth and the formation of the Local Bubble

“…Ellis et al (1996) identified several possible target isotopes for such a study, including 60 Fe (see also Korschinek et al 1996), which is believed to be produced primarily in core-collapse and electroncapture SNe of massive stars, with mass M 8 M , via successive neutron capture on preexisting Fe isotopes, both before and during the explosion (Timmes et al 1995;Wanajo et al 2013). Other suggested sources are asymptotic giant branch (AGB; Busso et al 2003) and super-AGB (SAGB; Lugaro et al 2012) stars, as well as a rare class of high-density thermonuclear SNe (Woosley 1997).…”