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Published byTimothy Young Modified over 9 years ago
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Nuclear Physics and Low-Metallicity Stellar Abundances: Victories and Struggles Chris Sneden, University of Texas speaking on behalf of many friends and colleagues in the stellar abundance & nucleosynthesis game
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Two main areas of interest to me 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
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A prime goal (and potential trap): understanding the solar chemical composition Sneden et al. 2008
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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-system dominance by r- or s- production Rolfs & Rodney (1988) The basic neutron-capture paths
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A detailed look at the r- and s-process paths Sneden et al. 2008 “s-process” element “r-process” element
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metal-poor n-capture-rich stars are common
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HST UV spectra yield exotic elements in brighter low-metallicity stars Roederer et al. 2012
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first detections of some elements, first believable abundances of other elements Roederer et al. 2012 see also Siqueira Mello Jr. et al. 2013
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the result is a “complete” abundance set Siqueira Mello Jr. et al. 2013 blue line: solar system scaled r-process log(X/H)+12 = log ε
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But we just keep trying to fit to the solar system abundance distribution Kratz et al. 2007
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hopefully, theoretical models are now catching up Siqueira Mello Jr. et al. 2013
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n-capture compositions of well-studied r-rich stars: Così fan tutte?? Sneden et al. 2008
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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(N A /N B ) star – log(N A /N B ) Sun
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This paper suggests that there is no known low metallicity star without neutron- capture elements Roederer 2013 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
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increasing evidence for non-solar r-processes Roederer et al. 2010
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this is a phenomenon extending to lots of stars Roederer et al. 2010
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But getting detailed neutron-capture abundances requires synthetic spectrum hand (very boring) computational effort
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maybe this is just r-process truncation at work Roederer et al. 2010 full? truncated?
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perhaps there is an easier way: just Sr, Ba, Eu, Yb being done with Jesse Palmerio, John Cown, Dick Boyd, Ian Roederer
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Why? Sr, Ba, Eu, Yb lines are simply strong
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Sr/Ba: assessment of LEPP issues Ba/Eu: assessment of r- or s- dominance Ba/Yb: assessment of r-process truncation being done with Jesse Palmerio, John Cown, Dick Boyd, Ian Roederer
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let’s turn to Fe-peak elements McWilliam 1997
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the “first stars” effort refined the quantitative answers but the qualitative trends stay the same Cayrel et al. 2004
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theoretical models can generate these elements Kobayashi et al. 2006
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and do so in ways that can be compared to observational observed trends Kobayashi et al. 2006
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there are good predictions for “zero-Z” models Heger & Woosley 2010
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for some elements the theory/observation match seems happy Kobayashi et al. 2006
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but for others, watch out! Kobayashi et al. 2006 same theory, different observed species of the same element
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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
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Fe-peak abundances in metal-poor stars: can you believe ANY analysis from the past?
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the outcome for Bergemann et al.? Are observers really saying that the Co/Fe ratio is 10x solar at lowest metallicities?
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A new initiative to on Fe-group abundances Kobayashi et al. 2006 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
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dotted line: no Fe in synthesis solid line: best fit dashed lines: ±0.5 dex from best fit red line: perfect agreement other lines: deviations why it is worth exploring the UV spectral region
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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)
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Ti obs/theory clashes are real, and must now be addressed Heger & Woosley 2010 Kobayashi et al. 2006
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more work to be done! theorists: please publish the numbers in neutron-capture predictions; continue exploring alternative ways to produce the Z=31-50 range observers: please produce Fe-group abundances that are useful for the theorists; especially support improvements in lab atomic and molecular physics
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fred
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Roederer et al. 2012
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