Speaker
Description
The abundance of decay products of radioactive, now extinct, isotopes in stardust grains can provide constraints on the formation time of these grains, which means the time between nucleosynthesis of a given radioactive isotope and grain formation. As common in dating schemes, the application requires a separation between the elements of the parent and the daughter isotope. An obvious way is difference in volatility so that one of the elements condenses into the grain, while the other does (almost) not.
The elements Cs and Ba, with the decay of 137Cs (half-life 30 a) into 137Ba, constitute such a pair. Barium has been found in supernova SiC grains (X grains), but Cs is too volatile and is not incorporated. From a subset of the few SiC-X1 grains analyzed so far we have previously derived a nominal formation time of 20 years after supernova explosion [1]. This is based on the relative abundance of 137Ba, in comparison with nucleosynthesis calculations that reproduce the Mo isotopic pattern of such grains [2, 3]. The so obtained age is surprisingly long compared to expectation.
In the REE mass region there are two pairs that might offer additional information. In mainstream SiC grains from AGB stars Eu and Sm are deficient relative to neighboring elements due to their higher volatility [4]. If this also applies to supernova SiC grains, dating might be possible using 155Eu (half-life 4.76 a) and 147Pm (half-life 2.62 a). Decay of 155Eu before grain formation would lead to 155Gd, ending up in the grain, while 155Eu still alive at grain formation would be excluded, leading to a deficit in 155Gd compared to the expected abundance after decay of precursors. Incorporation of Sm would be ineffective, while 147Pm still present would be incorporated and its subsequent decay within the grain could lead to (in the extreme) Sm that is almost mono-isotopic 147Sm.
Realizing the potential of the approach is challenging. It will require more isotopic analyses of heavy elements in supernova grains and improved understanding of supernova nucleosynthesis in the Ba / REE mass region.
References: [1] Ott U. et al. (2018), ApJ 885, 128. [2] Meyer B.S. et al. (2000), ApJL 540, L49. [3] Rauscher T. et al. (2002), ApJ 576, 323. [4] Yin Q.-Z. et al. (2006) ApJ 647, 676.
| Length of presentation requested | Oral presentation: 8 min + 2 min questions (Poster-type talk) |
|---|---|
| Please select between one and three keywords related to your abstract | Meteoritic Materials and Stardust |
