The Role of Fission on Neutron Star Merger Nucleosynthesis and its Impact on the r- Process Peaks Hirschegg, January 17, 2017 Marius Eichler (Univ. Basel, TU Darmstadt) DARMSTADT GEMEINSCHAFT U N I B A S E L
●  CS 22892-052: Sneden et al. (2003) ■ HD 115444: Westin et al. (2000) ◆  BD+17°324817: Cowan et al. (2002) *  CS 31082-001: Hill et al. (2002) ▶ HD 221170: Ivans et al. (2006) ◄  HE 1523-0901: Frebel et al. (2007) 2
Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg 3
Number of fission cycles N: 〈A〉i + Y n / Y seed N ~ log 2 | 〈A〉f 4
Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg 5
Barnes et al. 2016 Hotokezaka et al. 2016 Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg 6
Fission Fragments of ²⁷⁴Pu Panov et al. 2001 Kodama & Takahashi 1975 Panov et al. 2008 ABLA07 (Kelic et al. 2008) 17.01.2017
Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg
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. trajectories from a neutron star merger with two 1.4 M。neutron stars (Korobkin et al. 2012) . FRDM . difference between fission fragment distribution models mainly around and after  2nd peak . 3rd peak shifted to the right for all models Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg 8
Eichler et al. (2015) see also  Surman & Engel (2001) 9
. Aim: Identify the reactions responsible for certain features of the final abundance distribution . Procedure: Switch off certain types of reactions after freeze-out FRDM: 140 < A < 160 region depleted by neutron captures –
. HFB: 2nd and 3rd peak shifted, but not nuclei with 140 < A < 160
Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg
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Two possible sources for free neutrons at freeze-out: fission and β-decays β-decays enhanced after last fission cycle because very neutron rich fission fragments are produced Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg 12
. fission neutrons from the last fission cycle enforce neutron captures . affects mainly third peak and rare earths . β-decays of Z > 80 nuclei accelerated by factors of 2.5 and 6 . FRDM (1992) Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg 13
. β-decays of Z > 80 nuclei accelerated by factors of 2.5 and 6 . HFB-14 Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg 14
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Neutron star mergers: From gravitational waves to nucleosynthesis, Hirschegg
17 • after freeze-out, the abundance features can still be changed by several processes (e.g., neutron captures, fission) . in our NSM calculations, the third peak is shifted towards heavier nuclei due to neutron captures after the r-process freeze-out –  fission neutrons from last fission cycle . β-decays have a large influence on the global abundance distribution (also indirectly, i.e., by influencing the timing of the release of fission neutrons) Fission reactions are fundamental in shaping the r-process abundance pattern from the second peak onwards 18

University of Basel:
. F.-K. Thielemann . M. Liebendörfer . T. Rauscher . C. Winteler
TU Darmstadt / GSI:
. A. Arcones . G. Martinez-Pinedo . K. Langanke A. Kelic . . O. Korobkin (LANL) . S. Rosswog (Univ. Stockholm) . . T. Marketin (Univ. Zagreb) I. Panov (ITEP Moscow) N.T. Zinner (Aarhus Univ.) .