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

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

A prime goal (and potential trap):understanding the solar chemical composition

Sneden et al. 2008

• 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

A detailed look at the r- and s-process paths

Sneden et al. 2008

“s-process” element

“r-process” element

metal-poor n-capture-rich stars are common

HST UV spectra yield exotic elements in brighter low-metallicity stars

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first detections of some

elements, first believable

abundances of other elements

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see also Siqueira Mello Jr. et al. 2013

the result is a “complete” abundance setSi

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blue line: solar system scaled

r-process

log(X/H)+12 = log ε

But we just keep trying to fit to the solar system abundance distribution

Kratz et al. 2007

hopefully, theoretical models are now catching upSi

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n-capture compositions of well-studied r-rich stars: Così fan tutte??

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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

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

increasing evidence for non-solar r-processes

Roederer et al. 2010

this is a phenomenon extending to lots of stars

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

maybe this is just r-process truncation at work

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full?

truncated?

perhaps there is an easier way:

just Sr, Ba, Eu, Yb

being done with Jesse Palmerio, John Cown, Dick Boyd, Ian Roederer

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

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

let’s turn to Fe-peak elements

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the “first stars” effort refined the

quantitative answers but the

qualitative trends stay the same

Cayrel et al. 2004

theoretical models can generate these elements

Kobayashi et al. 2006 Koba

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and do so in ways that can be compared to observational observed trends

Kobayashi et al. 2006 Koba

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there are good predictions for “zero-Z” models

Heger & Woosley 2010

for some elements the theory/observation match seems happy

Kobayashi et al. 2006

but for others, watch out!

Kobayashi et al. 2006

same theory, different observed species of the same element

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

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

the outcome for Bergemann et al.?

Are observers really saying that the Co/Fe ratio is 10x solar at lowest metallicities?

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

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

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)

Ti obs/theory clashes are real,

and must now be addressed

Heger & Woosley 2010

Kobayashi et al. 2006

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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Roederer et al. 2012