Nuclear Physics and Low-Metallicity Stellar Abundances: Victories and Struggles

1. Nuclear Physics and Low-Metallicity Stellar Abundances: Victories and StrugglesChris Sneden, University of Texasspeaking on behalf of many friends and colleagues in the stellar abundance & nucleosynthesis game

2. Neutron-capture elements • Z > 30 (not all are due to neutron-capture?) • concentration on the r-process • “complete” abundance patterns now available? • departures from scaled-solar r-process • possible shortcuts to r-process enrichment • predicted abundance patterns lagging • current situation: observation ahead of theory • Fe-group elements • Z = 21-30 • lots of excellent supernova yields avaliable • some observed departures from solar abundance mix • but observations might not be trustworthy • steps underway to attack these worries • current situation: theory ahead of observation Two main areas of interest to me

3. A prime goal (and potential trap):understanding the solar chemical composition Sneden et al. 2008

4. The basic neutron-capture paths • s-process: β-decays occur between successive n-captures • r-process: rapid, short-lived neutron blast overwhelms β-decay rates • r- or s-process element: solar-systemdominance by r- or s- production Rolfs & Rodney (1988)

5. A detailed look at the r- and s-process paths “s-process” element “r-process” element Sneden et al. 2008

6. metal-poor n-capture-rich stars are common

7. HST UV spectra yield exotic elements in brighter low-metallicity stars Roederer et al. 2012

8. first detections of some elements, first believable abundances of other elements Roederer et al. 2012 see also SiqueiraMello Jr. et al. 2013

9. blue line: solar system scaled r-process log(X/H)+12 = log ε the result is a “complete” abundance set Siqueira Mello Jr. et al. 2013

10. But we just keep trying to fit to the solar system abundance distribution Kratz et al. 2007

11. hopefully, theoretical models are now catching up Siqueira Mello Jr. et al. 2013

12. n-capture compositions of well-studied r-rich stars: Così fan tutte?? Sneden et al. 2008

13. confusions remain about heavy versus light n-capture abundances was (unfortunately) named LEPP LEPP = lighter element primary process (Travaglio et al. 2004) [A/B] = log(NA/NB)star – log(NA/NB)Sun

14. This paper suggests that there is no known low metallicity star without neutron-capture elements upper limits in this figure are maybe just due to spectroscopic detection problems? on average the points to the lower left are lowest Fe metallicity stars Roederer 2013

15. increasing evidence for non-solar r-processes Roederer et al. 2010

16. this is a phenomenon extending to lots of stars Roederer et al. 2010

17. But getting detailed neutron-capture abundances requires synthetic spectrum hand (very boring) computational effort

18. full? maybe this is just r-process truncation at work truncated? Roederer et al. 2010

19. perhaps there is an easier way: just Sr, Ba, Eu, Yb being done with Jesse Palmerio, John Cown, Dick Boyd, Ian Roederer

20. Why? Sr, Ba, Eu, Yb lines are simply strong

21. Sr/Ba: assessment of LEPPissuesBa/Eu: assessment of r- or s- dominanceBa/Yb: assessment of r-process truncation being done with Jesse Palmerio, John Cown, Dick Boyd, Ian Roederer

22. let’s turn to Fe-peak elements McWilliam 1997

23. the “first stars” effort refined the quantitative answers but the qualitative trends stay the same Cayrel et al. 2004

24. theoretical models can generate these elements Kobayashi et al. 2006 Kobayashi et al. 2006

25. and do so in ways that can be compared to observational observed trends Kobayashi et al. 2006 Kobayashi et al. 2006

26. there are good predictions for “zero-Z” models Heger & Woosley 2010

27. for some elements the theory/observation match seems happy Kobayashi et al. 2006

28. but for others, watch out! same theory, different observed species of the same element Kobayashi et al. 2006

29. A typical metal-poor giant Fe-group abundance set there are very few lines for many species and we often are stuck observing the wrong species

30. Fe-peak abundances in metal-poor stars: can you believe ANY analysis from the past?

31. the outcome for Bergemann et al.? Are observers really saying that the Co/Fe ratio is 10x solar at lowest metallicities?

32. A new initiative to on Fe-group abundances this work concentrates on increasing accuracy of Fe-group elements the big point: must have better transition probabilities groups at Wisconsin, London, Belgium lead the way HST data at low metallicity end explores more species Kobayashi et al. 2006

33. why it is worth exploring the UV spectral region dotted line: no Fe in synthesissolid line: best fit dashed lines: ±0.5 dex from best fit red line: perfect agreementother lines: deviations

34. a quick report for today the big point: Ti I & Ti II give same answer; scatter is very low; Ti is really overabundant (Wood, Lawler, Guzman, Sneden, Cowan 2013)

35. Ti obs/theory clashes are real, and must now be addressed Kobayashi et al. 2006 Heger & Woosley 2010

36. more work to be done!theorists: please publish the numbers in neutron-capture predictions; continue exploring alternative ways to produce the Z=31-50 rangeobservers: please produce Fe-group abundances that are useful for the theorists; especially support improvements in lab atomic and molecular physics

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