Nuclear physics and the interpretation of r-process observables

Rebecca Surman University of Notre Dame

INT20-1b Online Pre-Workshop Institute of Nuclear Theory

7 April 2020 solar system abundances Burbidge, Burbidge, Fowler, and Hoyle 1957

r-process

from Smithsonian Frank Timmes Hendrik Schatz Artemis Spyrou

R Surman INT20-1b 7 April 20 Burbidge, Burbidge, Fowler, and Hoyle 1957

https://www.youtube.com/watch?v=nyvSoZe_q9A

R Surman INT20-1b 7 April 20 r-process nucleosynthesis

solar system r-process residuals

Arnould+2007 (n,γ) β

proton number Z (γ,n)

neutron number N € R Surman INT20-1b 7 April 20 € € r-process observables: abundance patterns

solar system r-process residuals

Arnould+2007, Hotokezaka+2018 elemental abundances from r-process-enhanced metal-poor stars

R Surman INT20-1b 7 April 20 Electromagnetic counterpart to

16 Barnes et al.r-process observables: kilonovae the neutron star merger GW signal 17 Kilpatrick+2017, Kasen+2017, etc. 16 GW170817 15 kilonova SSS17a bolometric light curve 14 SSS17a bolometric

AB 13 ) Mej = 0.01M , vej = 0.1c J ( 12 M = 0.05M , v = 0.1c

M ej ej 11 Mej = 0.05M , vej = 0.2c bolometric compilation: Waxman+ 2017 10 models: Kasen+2017 Mej = 0.1M , vej = 0.2c 9 Mej = 0.1M , vej = 0.1c 8 lanthanide rich 100 101 Days lanthanide poor Barnes+2016 Figure 17. Absolute (AB) J -band light curves for several ejecta models.sGRB The130603B: excess IRTanvir+2013 flux (gold star) suggests an ejected mass 2 1 between 5 10 and 10 M . ⇥ winds. Our mass estimate here is an improvement over earlier work which neglected detailed thermalization, and gives R Surman INT20-1b 7 April 20 substantially di↵erent results. For example, Piran et al. (2014) suggested Mej 0.02M , less than half our new value. However, we have⇠ not accounted Material for viewing with an- significant opacity is the best fit to the data Slide credit: Dan gle e↵ects. If the ejected material is mainly confined to the equatorial plane, the emissionKasan will beSuggests brighter when lanthanides were made in the r-process. the system is viewed face-on (Roberts et al. 2011), which would reduce the inferred mass somewhat. If the ejecta is oblate, thermalization will also be more ecient, which could have a small impact on mass estimates. Radia- tion transport simulations in three dimensions with time- dependent thermalization models will further constrain Mej. 6.4. Late-time light curve Figure 16. Synthetic bolometric light curves for our fiducial ejecta model, calculated with Sedona for three di↵erent treatments Late time kilonova light curves may probe the history of thermalization: full thermalization (blue curve); Sedona’s origi- of r-process nucleosynthesis in CO mergers. At 2days nal thermalization scheme, which deposits charged particle energy after merger, fission ceases to be important, and⇠↵- and but explicitly tracks the deposition of -ray energy (lime curve); -decay dominate the kilonova’s energy supply. Energy and the time-dependent ftot(t)fromournumericalsimulations(red curve). Accounting for time-dependent thermalization eciencies from ↵-decay is transferred entirely to fast ↵-particles, has a significant impact on kilonova luminosity, particularly for which thermalize fairly eciently out to late times. Beta models with lower masses and higher luminosities. For our fiducial particles thermalize with similar eciency, but carry only model, the predicted luminosity is lower by a factor of . 2atpeak, a fraction ( 25%) of the total -decay energy, with the and by 10 days is lower by an factor of 5. rest lost to⇠ neutrinos and -rays. A kilonova’s late-time luminosity will therefore depend on the relative impor- 2013; Berger et al. 2013). Tanvir et al. (2013)deter- tance of ↵-versus-decay. Because only nuclei with mined that the source of the flux had an absolute AB 200 . A . 250 undergo ↵-decay, the late time kilonova magnitude in the J -band of -15.35 at t 7 days. Having luminosity may diagnose the presence of heavy elements ⇠ incorporated ftot(t) into kilonova light curve models, we in the ejecta, and therefore constrain the neutron-rich can more confidently constrain the mass ejected in the conditions required for heavy element formation. kilonova associated with GRB 130603B. We gauge the relative strength of late-time kilonova In Figure 17, we compare the detected flux to J -band light curves for di↵erent Ye,0 by estimating the percent light curves for various ejecta models, and find the ob- of energy from the decay of r-process elements emitted 2 served flux is consistent with 5 10 M . Mej . as fission fragments, ↵-, and -particles, time-averaged 1 ⇥ 10 M . This mass is higher than what is typically pre- over t = 10 100 days. (Note that while all energy from dicted for the dynamical ejecta from a binary neutron ↵-decay emerges as ↵-particles, -particles receive only star merger, suggesting that if the kilonova interpreta- 25-30% of the energy from -decay.) The results for our tion is correct, the progenitor of GRB 130603B was per- representative SPH trajectory, for a range of Ye,0 and haps a neutron star-black hole merger, or that the mass two nuclear mass models, are shown in Figure 18.The ejected was significantly enhanced by post-merger disk curves suggest that systems with Ye,0 . 0.17 have more 8

neutron star merger r-process environments

t t = 0.3 ms t t = 0.6 ms ≠ mrg ≠ ≠ mrg prompt ejecta

Ye 2 A. Perego et al. Radice+2019

ejecta from the accretion disk

Perego+2014 t t = 1.2 ms t t = 2.5 ms R Surman≠ mrg INT20-1b ≠ mrg 7 April 20

Figure 2. Volume rendering of the electron fraction of the ejecta for the simulation SFHo M135135 M0.Theray-castingopacityislinear in the logarithm of the rest-mass density. From the top-left in clockwise direction, the transparency minimum – maximumFigure in the opacity 1. Left: sketch of the neutrino-driven wind from the remnant of a BNS merger. The hot hypermassive neutron star (HMNS) scale are (1011 1014)gcm 3,(108 1011)gcm 3,(108 1011)gcm 3,and(107 1011)gcm 3.Thelastpanelofthisfigureshouldand the accretion disc emit neutrinos, preferentially along the polar direction and at intermediate latitudes. A fraction of the neutrinos be compared with Fig. 14 where we plot a cut of the data in the xz-plane. is absorbed by the disc and can lift matter out of its gravitational potential. On the viscous time-scale, matter is also ejected along the equatorial direction. Right: sketch of the isotropised ⌫ luminosity we are using for our analytical estimates (see the main text for details).

decompression of this initially cold and extremely neutron- et al. 2014) for the so-called “macro-” or “kilonovae” (Li rich nuclear matter had long been suspected to provide & Paczy´nski 1998; Kulkarni 2005; Rosswog 2005; Metzger favourable conditions for the formation of heavy elements et al. 2010a,b; Roberts et al. 2011), radioactively powered through the rapid neutron capture process (the “r-process”) transients from the decay of freshly produced r-process (Lattimer & Schramm 1974; Lattimer & Schramm 1976; elements. In particular, the delay of several days between Lattimer et al. 1977; Symbalisty & Schramm 1982; Eichler the sGRB and the nIR detection is consistent with the et al. 1989; Meyer 1989; Davies et al. 1994). While initially expanding material having very large opacities, as predicted only considered as an “exotic” or second-best model behind for very heavy r-process elements (Kasen et al. 2013). If core-collapse supernovae, there is nowadays a large litera- this interpretation is correct, GRB130603B would provide ture that –based on hydrodynamical and nucleosynthetic the first observational confirmation of the long-suspected calculations– consistently finds that the dynamic ejecta of a link between compact binary mergers, heavy elements neutron star merger is an extremely promising site for the nucleosynthesis and gamma-ray bursts. formation of the heaviest elements with A>130 (see, e.g., There are at least two more channels, apart from the Rosswog et al. 1999; Freiburghaus et al. 1999; Oechslin dynamic ejecta, by which a compact binary merger re- et al. 2007; Metzger et al. 2010b; Roberts et al. 2011; leases matter into space, and both of them are potentially Goriely et al. 2011a,b; Korobkin et al. 2012; Bauswein et al. interesting for nucleosynthesis and –if enough long-lived 2013; Hotokezaka et al. 2013; Kyutoku et al. 2013; Wanajo radioactive material is produced– they may also power et al. 2014). Core-collapse supernovae, on the contrary, additional electromagnetic transients. The first channel seem seriously challenged in generating the conditions that is the post-merger accretion disc. As it evolves viscously, are needed to produce elements with A>90 (Arcones et al. expands and cools, the initially completely dissociated 2007; Roberts et al. 2010; Fischer et al. 2010; H¨udepohl matter recombines into alpha-particles and –together with et al. 2010). A possible exception, though, may be magnet- viscous heating– releases enough energy to unbind an ically driven explosions of rapidly rotating stars (Winteler amount of material that is comparable to the dynamic et al. 2012; M¨osta et al. 2014). Such explosions, however, ejecta (Metzger et al. 2008; Beloborodov 2008; Metzger require a combination of rather extreme properties of the et al. 2009; Lee et al. 2009; Fern´andez & Metzger 2013). pre-explosion star and are therefore likely rare. The second additional channel is related to neutrino-driven Most recently, the idea that compact binary mergers are winds, the basic mechanisms of which are sketched in Fig. 1. related to both sGRBs and the nucleosynthesis of the This wind is, in several respects, similar to the one that heaviest elements has gained substantial observational emerges from proto-neutron stars. In particular, in both support. In June 2013, the SWIFT satellite detected a cases a similar amount of gravitational binding energy is relatively nearby (z =0.356) sGRB, GRB130603B, (Me- released over a comparable (neutrino di↵usion) time-scale, 53 landri et al. 2013) for which the Hubble Space Telescope which results in a luminosity of L⌫ Egrav/⌧di↵ 10 ⇠ ⇠ (Tanvir et al. 2013; Berger et al. 2013a) detected a nIR erg/s and neutrinos with energies 10 15 MeV. Under ⇠ point source, 9 days after the burst. The properties of this these conditions, energy deposition due to neutrino absorp- second detection are close to model predictions (Kasen tion is likely to unbind a fraction of the merger remnant. et al. 2013; Barnes & Kasen 2013; Tanaka & Hotokezaka In contrast to proto-neutron stars, however, the starting 2013; Grossman et al. 2014; Rosswog et al. 2014a; Tanaka point is extremely neutron-rich nuclear matter, rather than

c year RAS, MNRAS 000,1–25 open questions in nsm/r-process nucleosynthesis

Can we understand neutron star merger nucleosynthesis from first principles?

Are neutron star mergers responsible for the production of all r-process elements, or do multiple distinct sites contribute?

R Surman INT20-1b 7 April 20 movie by N. Vassh using PRISM (Sprouse/Mumpower)

Trevor Sprouse, TEAMS/ND grad student nuclear data for r-process simulations

masses beta-decay rates beta-delayed neutron emission probabilities neutron capture rates

fission rates fission product distributions neutrino interaction rates spallation cross sections

Mumpower, Surman, McLaughlin, Aprahamian Progress in Particle and Nuclear Physics 86 (2016) 86

R Surman INT20-1b 7 April 20 nuclear data for r-process simulations: masses

masses Mumpower+2016 beta-decay rates beta-delayed neutron emission probabilities neutron capture rates

fission rates fission product distributions neutrino interaction rates spallation cross sections

masses from AME2016

R Surman INT20-1b 7 April 20 impact of mass uncertainties Abundance pattern ranges for 10 distinct mass models on abundance patterns

Abundance pattern ranges for 50 sets of masses calculated with the UNEDF1 functional

1 ) A

( 0.1 Y

0.01

120 130 140 150 160 170 180 190 200 A Sprouse, Navarro Perez, Surman, McLaughlin, Mumpower, Schunk arXiv:1901.10337, accepted in PRC Côté, Fryer, Belczynski, Korobkin, Chruślińska, Vassh, Mumpower, Lippuner, Sprouse, Surman, Wollaeger 2018

R Surman INT20-1b 7 April 20 experimental prospects: masses

AME 2016 FRIB Day 1 reach FRIB design goal

R Surman INT20-1b 7 April 20 experimental prospects: masses

high entropy wind

low entropy wind

nsm dynamical ejecta

Sprouse, Navarro Perez, Surman, McLaughlin, Mumpower, Schunk arXiv:1901.10337, accepted in PRC R Surman INT20-1b 7 April 20 Electromagnetic counterpart to

kilonovathesignatures neutron star merger GW signal

kilonova SSS17a bolometric light curve

SSS17a bolometric

bolometric compilation: Waxman+ 2017 models: Kasen+2017

lanthanide rich

lanthanide poor

R MaterialSurman INT20- with1b significant opacity is the best fit to the data Slide credit: Dan7 April 20

Kasan Suggests lanthanides were made in the r-process. signature of actinide production?

frame from simulation by N. Vassh using PRISM (Sprouse, Mumpower)

R Surman INT20-1b 7 April 20 254Cf and late-time radioactive heating

Zhu, Wollaeger, Vassh, Surman, Sprouse, Mumpower, Möller, McLaughlin, Korobkin, Jaffke, Holmbeck, Fryer, Even, Couture, Barnes, ApJL 2018

R Surman INT20-1b 7 April 20 254Cf: nuclear uncertainties

Vassh, Vogt, Surman, Randrup, Sprouse, Mumpower, Jaffke, Shaw, Holmbeck, Zhu, McLaughlin, J Phys G 2019

R Surman INT20-1b 7 April 20 abundance pattern signatures

Arnould+2007, Hotokezaka+2018

R Surman INT20-1b 7 April 20 abundance pattern signatures spallation and the 3rd peak

actinide boost Arnould+2007, Hotokezaka+2018

mass model reverse engineering for rare earth peak formation

R Surman INT20-1b 7 April 20 actinide production: clues from metal-poor stars Mashonkina et al.: HE 2252−4225, one more r-process enhanced and actinide boost star Mashonkina+2010 species, the dispersion in the singleactinide line measurements boost? around the mean does not exceed 0.12 dex. The investigated star was found to be deficient in carbon, as expected for a giant star with Teff < 4800 K. The elements in the range from Na to Zn reveal atypicalbehaviourofthegalactichaloVMPstars.TheNa–Zn abundance pattern of HE 2252−4225 is well fitted by the yields of a single supernova of 14.4 M⊙,similartotheLaietal.(2008) stellar sample. We confirmed that HE 2252−4225 is r-process enhanced, having [r/Fe] = 0.80 ± 0.06. The investigated star and four benchmark r-II stars; i.e., CS 22892-052 (Sneden et al. 2003), CS 31082-001 (Siqueira Mello et al. 2013), HE 1219- 0312 (Hayek et al. 2009), and HE 1523-091 (Sneden et al. 2008) have very similar abundance patterns of the elements in the range from Sr to Ir. Hence, neutron-capture elements beyond Sr and up to Ir in HE 2252−4225 have a common origin in the classi- Fig. 9. Th/Eu abundance ratioselemental of the Roedererabundances et al. cal main r-process. Applying the third criterion, [Sr/Eu] < −0.8 − (2009) sample, HE 2327 5642from (Paper r-process V), CS-enhanced 30315-029 (Mashonkina et al. 2010), in addition to the two, [Eu/Fe] > +1 (Siqueira-Mello et al. 2014), and HE 2252−4225 (filled rhomb metal-poor stars and [Ba/Eu]Cowan+2011< 0, as suggested by Christlieb et al. (2004), makes inside open circle). Stars with high Th/Eu ratios (log(Th/Eu) membership to r-II stars have a physical sense related to an ori- ≥−0.35) are shown by filled rhombi and the remaining stars gin of the neutron-capture elements in the star; i.e., an r-IIstar withR Surman open rhombi.INT20-1b The horizontal lines indicate the ratios ex- can be defined as a star having neutron-capture elements7 April orig 20 i- pected if a sample of material had a given age, assuming the nating in a single r-process. solar r-process of Bisterzo2014. We tested the solar r-process pattern based on recent s- process calculations of Bisterzo et al. (2014) and found thatthe elements in the range from Ba to Ir in HE 2252−4225 match it 13.772 ± 0.059 Gyr (Bennett et al. 2013) derived from the up- very well. No firm conclusion can be drawn about the relation- dated results of the Wilkinson Microwave Anisotropy Probe ship between the first neutron-capture peak elements, Sr to Ru, (WMAP).Forexample,τ = 14.9 ± 6.5Gyrwascalculated in HE 2252−4225 and the solar r-process, owing to the uncer- for CS 22892-052 with log(Th/Eu) = −0.64. The remaining tainty in the solar r-process. six stars, namely, CS31082-001, CS30306-132 (discovered by The star HE 2252−4225 has an anomalously high Th/Eu Honda et al. 2004), CS31078-018 (Lai et al. 2008), HE1219- abundance ratio, so that radioactive age dating results in a stellar 0312 (Hayek et al. 2009), CS 30315-029 (Siqueira-Mello et al. age of τ = 1.5±1.5Gyrthatisnotexpectedforaverymetal-poor 2014), and HE 2252−4225, exhibit an actinide boost, and their halo star. This is the sixth star in the group of actinide booststars. ages cannot be derived when only a single radioactive element Understanding the mechanisms resulting in different yields in Th is detected. Indeed, a negative age of τ = −4.7Gyriscalcu- the actinide region from different r-process events is a challenge lated for CS 31082-001, when using the Th/Eu abundance ratio. for nucleosynthesis theory and requires studying larger samples This implies that thorium in the actinide boost stars was overpro- of r-I and r-II stars. duced compared with the normal Th/Eu stars and the SS matter. Only the detection of the second actinide, uranium, made pos- Acknowledgements. This work was supported by Sonderforschungsbereich SFB sible an estimation of the stellar age of CS31082-001 through 881 “The Milky Way System” (subprojects A4 and A5) of the German Research analysis of U/Th; i.e., τ = 12.5 ± 3Gyrwasfirstobtainedby Foundation (DFG). L.M. is supported by the Russian Foundation for Basic Research (grant 14-02-91153) and the Swiss National ScienceFoundation Cayrel et al. (2001), and the revised value is τ = 14.0 ± 2.4Gyr (SCOPES project No. IZ73Z0-152485). We made use the NIST and VA L D (Hill et al. 2002). This provided solid evidence that different r- databases. process nucleosynthesis events may produce significantly differ- ent yields in the actinide region (Z ≥ 90). To find out whether variations in progenitor mass or explosion energy, or other in- References trinsic and environmental factors, or all of these, influencethe Alexeeva, S., Pakhomov, Y., & Mashonkina, L. 2014, AstronomyLetters,40, r-process yields for the heaviest elements, more measurements 406 of Th and U abundances in stars should be done. Andrievsky, S. M., Spite, M., Korotin, S. A., et al. 2010, A&A,509,A88 Andrievsky, S. M., Spite, M., Korotin, S. A., et al. 2008, A&A,481,481 Anstee, S. D. & O’Mara, B. J. 1995, MNRAS, 276, 859 Aoki, W., Beers, T. C., Honda, S., & Carollo, D. 2010, ApJ, 723,L201 7. Conclusions Aoki, W., Frebel, A., Christlieb, N., et al. 2006, ApJ, 639, 897 Aoki, W., Honda, S., Beers, T. C., et al. 2005, ApJ, 632, 611 We revised the stellar parameters and performed a detailed Arlandini, C., K¨appeler, F., Wisshak, K., et al. 1999, ApJ, 525, 886 abundance analysis of the VMP giant HE 2252−4225 using Bagnulo, S., Jehin, E., Ledoux, C., et al. 2003, The Messenger, 114, 10 high-quality VLT/UVES spectra and refined theoretical methods Bard, A., Kock, A., & Kock, M. 1991, A&A, 248, 315 Barklem, P. S. & Aspelund-Johansson, J. 2005, A&A, 435, 373 of line-formation modelling. The effective temperature, T ff = e Barklem, P. S., Belyaev, A. K., Dickinson, A. S., & Gad´ea, F. X. 2010, A&A, 4710 K, previously derived in Paper II was confirmed through 519, A20 analysis of the Hα and Hβ line wings in HE 2252−4225. The sur- Barklem, P. S., Belyaev, A. K., Spielfiedel, A., Guitou, M., & Feautrier, N. 2012, face gravity, log g = 1.65, the iron abundance, [Fe/H] = −2.63, A&A, 541, A80 −1 Barklem, P. S., Christlieb, N., Beers, T. C., et al. 2005, A&A,439,129,(Paper and the microturbulence velocity, ξt = 1.7kms ,werecalcu- i ii II) lated from the NLTE ionisation balance between Fe and Fe . Barklem, P. S. & O’Mara, B. J. 1997, MNRAS, 290, 102 Accurate abundances for a total of 38 elements from C Barklem, P. S. & O’Mara, B. J. 1998, MNRAS, 300, 863 to Th were determined in HE 2252−4225. For each chemical Barklem, P. S., O’Mara, B. J., & Ross, J. E. 1998, MNRAS, 296, 1057

12 actinide production in r-process simulations

3 L 10 Ye A Ye 4 N 10 Ye

Y(A) 5 10

6 10 120 140 160 180 200 220 240 Erika Holmbeck, A JINA-CEE/ND grad student Th 3 U Eu 4 5 log Y(Z) Holmbeck, Sprouse, Mumpower, 6 Vassh, Surman, Beers, Kawano 2019 50 60 70 80 90 Z

R Surman INT20-1b 7 April 20 actinide dilution + matching model

Ret II Group F J0954+5246 1 10

Mass fraction 2 10 accretion disk outflows are expected to be less ⌫e + n p + e dynamical ejecta is neutron-rich ! expected to be very ⌫¯ + p n + e+ 0.5 0.4 0.3 0.e2 0.!1 0.0 neutron-rich Ye 1 Y = Holmbeck, Frebel, McLaughlin, e 1+(n/p) Mumpower, Sprouse, Surman 2019

R Surman INT20-1b 7 April 20 spallation of r-process nuclei

spallation r-process nucleus l

r-process ISM nucleus light nucleus nucleus i j (H/He) (p,n,a,etc.)

NSM outflows ~ 0.1-0.5c Wang, Fields, Mumpower, Sprouse, Surman, Vassh, r process ejecta arXiv:1909.12889 accepted in ApJ NSM spallation & ionic loss

R Surman INT20-1b 7 April 20 spallation and the A ~ 195 peak

Xilu Wang, N3AS/ND postdoc

Wang, Fields, Mumpower, Sprouse, Surman, Vassh, arXiv:1909.12889 accepted in ApJ

R Surman INT20-1b 7 April 20 2 in r-process calculations predict a nuclear physics fea- ture away from stability that leads to dynamical rare earth peak formation, e.g. [41], though the peak is not always of the correct size and shape to match the so- lar pattern. Other mass models, e.g. [42], show no such feature. Carefully-chosen linear combinations of astro- physical conditions have been shown to improve the fit to observation [43, 44]. An alternate formation mecha- nism has been proposed that suggests the rare earth peak is made up of fission fragments resulting from a vigorous fission recycling r process [45]. This mechanism hinges upon a specific distribution of fission daughter products [46] that is untestable by experiment. Thus, it can only be supported by indirect evidence, including the elimina- tion of the dynamical mechanism as a viable alternative. In this letter, we introduce a new method by which the nuclear structure features that are necessary to produce characteristics of the r-process abundance pattern are determined by a Monte Carlo analysis. We apply this FIG. 1: Simulations of the r process with no rare earth peak procedure to the portion of the isotopic solar abundances in hot (red solid line) and very neutron-rich cold (green dashed line) conditions compared to the solar r-process residuals from that includes the rare earth region, and we search for Ref. [9] (black points). a persistent, non-local feature in the mass surface that leads to dynamical rare earth peak formation matching the solar pattern. There are two generic types of thermodynamic condi- results of r-process simulations with this set of nuclear tions that could exist toward the end of the r process. data are shown by the red and green curves in Fig. 1 for We define “hot” environments as those where the mate- a hot and a cold very neutron-rich scenario, respectively. rial stays in (n, ) (,n) equilibrium until the neutron As expected the abundance pattern shows no feature in number is no longer suciently high to maintain this the rare earth region. This suggests the DZ mass model equilibrium and “cold” environments as those where the is missing the ingredient that leads to dynamical rare equilibrium is broken because the temperature becomes earth peak formation. too low. A standard supernova neutrino wind is a hot Since we have a baseline model without structure in environment whereas the ejection of material from the the rare earth region we are free to determine the missing tidal tails of neutron star mergers is both cold and very component of the mass model which is required to match neutron rich. We apply our Monte Carlo procedure to the r-process residuals. Previous studies have suggested both types of environments. that a kink in the separation energies as a function of As few mass measurements currently exist in the re- neutron number is required [38, 39], but we wish to start gion in which we are interested, we require a theoretical with asdeducing little preconceived r-process notion as possible conditions about what from abundance baseline mass model. For our baseline model, we choose this structure should be. Therefore, instead of choos- Duflo-Zuker (DZ) [47] since it has little structure in the pattern details: the rare earth peak ing a parameterized form for a kink structure, we let an masses away from stability in the rare earth region. To additional mass term float freely in neutron number, N: verify this, we use the DZ mass model to compute neu- mass modification parameterization: tron capture and beta decay rates and then run a set (Z C)2/2f M(Z, N)=MDZ(Z, N)+aN e (1) of r-process simulations for di↵erent astrophysical condi- tions. The neutron capture rates are computed using the Here, M(Z, N) is the new mass generated from the base- Hauser-Feshbach code CoH [48]. For the -decay rates, line DZ mass,hot, (n,MgDZ)-(g(,nZ,) N), where Z and N represent the equilibrium we use the underlying Gamow-Teller -decay strength number of protons and neutrons in the nucleus. The aN function, i.e. the nuclear matrix element information, are coecients, one for each set of isotones with neutron from [49]. We compute the phase space factor to be con- number, spanning the range from 95 to 115. For a given sistent with the DZ masses, as in Ref. [50]. Our treatment neutron number,cold, verya controls the overall magnitude and neutron-richN of fission is largely schematic, as in [51], with spontaneous sign of the change to the base model. The parameter C fission set to occur for A>240 and a simple asymmetric controls the center of the strength in proton number, and Mumpower, McLaughlin, Surman, Steiner, 2016 split assumed for the fission daughter product distribu- f sets the fall o↵ the strength in Z. The latter we keep tions. This allows us to explore scenarios with fission fixed at f = 40 because we are looking for a persistent recycling where the fission fragments (A 130) do not feature in the mass surface. ⇠ contribute to rare earth peak formation. Examples of the WeR Surman now proceedINT20-1b to determine the aN s and C using the 7 April 20 reverse-engineering results for a hot wind r-process

Nicole Vassh, Orford, Vassh+ PRL 2018 FIRE/ND postdoc

R Surman INT20-1b 7 April 20 reverse-engineering results for a hot wind r-process + new experimental masses

masses from CPT at CARIBU

astrophysical conditions of a hot, (n,g)-(g,n) equilibrium wind Orford, Vassh+ PRL 2018

R Surman INT20-1b 7 April 20 reverse-engineering results for three distinct scenarios

PRELIMINARY Vassh+ in preparation

R Surman INT20-1b 7 April 20 summary The origin of the heaviest elements in the r-processThe ofNumber nucleosynthesis of Isotopeshas Available for Study been one of the greatest mysteries in nuclear astrophysics for decades.at FRIB

Evidence from a variety of directions ! Estimated Possible: Erler, increasingly points to neutron star mergers Birge, Kortelainen, as an important source of r-process Nazarewicz, Olsen, elements, but more work is needed, e.g., Stoitsov, Nature 486, 509– 512 (28 June 2012) , advances in astrophysical modeling, based on a study of EDF neutrino physics, and nuclear theory and models experiment. ! “Known” defined as isotopes with at least one On the nuclear side, the next generation of excited state known (1900 radioactive beam facilities offers great isotopes from NNDC database) promise to reach the increasingly neutron- ! For Z<90 FRIB is rich nuclei whose properties may provide predicted to make > 80% key insight into the astrophysical conditions of all possible isotopes of r-process production.

Nuclear Structure 2012 - Sherrill , Slide 11