nuclear physics and low-metallicity stellar abundances: victories and struggles chris sneden,...
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![Page 1: Nuclear Physics and Low-Metallicity Stellar Abundances: Victories and Struggles Chris Sneden, University of Texas speaking on behalf of many friends and](https://reader035.vdocument.in/reader035/viewer/2022070415/5697c02b1a28abf838cd881f/html5/thumbnails/1.jpg)
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
Roed
erer
et a
l. 20
12
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first detections of some
elements, first believable
abundances of other elements
Roed
erer
et a
l. 20
12
see also Siqueira Mello Jr. et al. 2013
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the result is a “complete” abundance setSi
quei
ra M
ello
Jr. e
t 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 upSi
quei
ra M
ello
Jr. e
t al.
2013
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n-capture compositions of well-studied r-rich stars: Così fan tutte??
Sned
en e
t 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(NA/NB)star – log(NA/NB)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
Roed
erer
et a
l. 20
10
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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
Roed
erer
et a
l. 20
10
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
McW
illia
m 1
997
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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 Koba
yash
i et a
l. 20
06
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and do so in ways that can be compared to observational observed trends
Kobayashi et al. 2006 Koba
yash
i et a
l. 20
06
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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 elementsthe big point: must have better transition probabilitiesgroups at Wisconsin, London, Belgium lead the wayHST data at low metallicity end explores more species
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dotted line: no Fe in synthesissolid line: best fit dashed lines: ±0.5 dex from best fit
red line: perfect agreementother 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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fred
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fred
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fred
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fred
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fred
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fred
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fred
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fred
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fred
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fred
Roederer et al. 2012