Transcript ppt

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
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-system dominance by r- or s- production
Rolfs & Rodney (1988)
A detailed look at the r- and s-process paths
“s-process”
element
“r-process”
element
Sneden et al. 2008
metal-poor n-capture-rich stars are common
Roederer et al. 2012
HST UV spectra yield exotic elements in
brighter low-metallicity stars
Roederer et al. 2012
first detections of
some elements,
first believable
abundances of
other elements
see also Siqueira Mello Jr.
et al. 2013
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
But we just keep trying to fit to the solar
system abundance distribution
Kratz et al. 2007
Siqueira Mello Jr. et al. 2013
hopefully, theoretical models are now catching up
Sneden et al. 2008
n-capture compositions of well-studied
r-rich stars: Così fan tutte??
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 neutroncapture 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
increasing evidence for non-solar r-processes
Roederer et al. 2010
Roederer et al. 2010
this is a phenomenon extending to lots of stars
But getting detailed neutron-capture
abundances requires synthetic spectrum hand
(very boring) computational effort
maybe this is just r-process truncation at work
Roederer et al. 2010
full?
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
McWilliam 1997
let’s turn to Fe-peak elements
the “first stars”
effort refined the
quantitative
answers but the
qualitative trends
stay the same
Cayrel et al. 2004
Kobayashi et al. 2006
Kobayashi et al. 2006
theoretical models can generate these elements
Kobayashi et al. 2006
Kobayashi et al. 2006
and do so in ways that can be compared to
observational observed trends
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!
same theory, different
observed species of the
same element
Kobayashi et al. 2006
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
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
why it is worth exploring the UV spectral region
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
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
Kobayashi et al. 2006
Heger & Woosley 2010
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