Early Galactic Nucleosynthesis: The Impact ofHST/STIS Spectra of Metal-Poor Stars
Chris SnedenUniversity of Texas
A Very Collaborative Effort
Definitions:
[A/B] = log10(NA/NB)star – log10(NA/NB)Sun
log ε(A) = log10(NA/NH) + 12.0 (spectroscopic)
log N(A) = log10(NA/NSi) + 6.0 (meteoritic)
today two topics:- the neutron-capture elements- return to the Fe-peak
the common thread: nucleosynthesis at the end of stellar lives
HST/STIS spectra: relevant to entire nuclide range
Heaviest stable elementsa.k.a 3rd neutron-capture peak
Understudied lighter neutron-capture elements
Fe-group elements
Light elements (Be, B)
http://atom.kaeri.re.kr/
The ultimate question? How did our Galaxy produce the solar chemical composition?
SCG08 = Sneden, Cowan, & Gallino 2008, ARA&A, 46, 241
Most isotopes of elements with Z>30 are formed by: AZ + n A+1ZFollowed by, for unstable nuclei: A+1Z A+1(Z+1) + -
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I
ScCaK
Xe
Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
H
BeLi
MgNa
Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
RaFr
BaCs
Rf Db Sg Bh Hs Mt Uun Uuu Uub
CB O F Ne
ArAl Si P S Cl
N
He
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
First discussion: n(eutron)-capture elements
• s-process: β-decays occur between successive n-captures• r-process: rapid, short-lived neutron blast temporarily • overwhelms β-decay rates• r- or s-process element: origin in solar-system • dominated by one or the other process
Rolfs & Rodney (1988)
Buildup of n-capture elements
A detailed look at the r- and s-process paths
SCG08
“s-process” element
“r-process” element
n-capture spectra of metal-poor stars
HD 122563:[Fe/H] = -2.7Teff ~ 4750LOW n-capture
CS 22892-052:[Fe/H] = -3.1Teff ~ 4750HIGH n-capture
“r-process-rich” metal-poor stars
first example, HD 115444, was reported by Griffin et al. 1982 SCG08
An important abundance ratio:log (La/Eu) = +0.6 (solar total) = +0.2 (solar r-only) = +1.5 (solar s-only)
HfBa La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu
Wisconsin lab studies: log gf and hyperfine/isotopic structureLa
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14 36 14 20 2 13 3 8 3 1 1 445 5 46Sun: # transitions used in analysis
1532154 7 29 13 21 6 1 837 55 9 32CS 22892-052 : # transitions used in analysis
why are rare earths well understood?
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n-capture compositions of well-studied r-rich stars: Così fan tutte??
SCG08
lines are solar-system abundances
differences fromsolar-system
means of the differences
Thorium/Uranium detections promise alternate Galactic ages
Frebel et al. 2007
leading to possible radioactive decay ages
U/Th ratio should be best age
indicator, if both elements can be detected reliably
Persistent question: why is Pb usually low?
Frebel et al. 2007
good abundances really confront r-process predictions
Ivans et al. 2006
But! crucial element groups for further progress
Ivans et al. 2006
Johnson & Bolte 2002
Beyond simplest results: de-coupling of the heavy/light r-
process elements
See also Aoki et al. 2005, 2007
ZY = 39ZBa = 56
r-process abundance distribution variations: "normal"
Roederer et al 2010
But various densities must contribute to r-process
Kratz et al. 2007
increasing density components
decreasing density components
Niobium (Nb, Z=41): surrogate for
remaining n-capture elements (and their
“issues”)
these are the best transitions in the most favorable detection cases
Nilsson et al. 2010
All reasonably strong lines are in the vacuum UV;
this is why STIS is good here
Niobium: here is why there are difficulties
Nilsson et al. 2010
UV spectra of 3 metal-poor giants
Roederer et al 2010
HD 122563:[Fe/H] = -2.7Teff ~ 4750LOW n-capture
HD 115444:[Fe/H] = -2.9Teff ~ 4650HIGH n-capture
BD+17 3248[Fe/H] = -2.2Teff ~ 5200HIGH n-capture
Initial STIS exploration
HD 122563:[Fe/H] = -2.7Teff ~ 4750LOW n-capture
HD 115444:[Fe/H] = -2.9Teff ~ 4650HIGH n-capture
CS 22892-052[Fe/H] = -3.1Teff ~ 4750HIGH n-capture
Cowan et al. 2005
Heaviest stable elements scale
with Eu
Cowan et al. 2005
Again, Eu is the usual “pure” r-process element
But light n-capture elements do NOT
scale with Eu
Cowan et al. 2005
Upon further review of these same STIS data …
Roederer et al 2010
Points = data
Lines = syntheses:• best fit (color)• ± 0.3dex (dotted)• no element (solid)
Helps “complete” the n-capture distribution
Roederer et al 2010
Points = observations
Blue line = SN ν windFarouqi et al. 2009
Gray lines = scaled solar-system
Second discussion: back to the Fe-peak
McWilliam 1997
sharpening & extension by “First Stars” group
Cayrel et al. 2004
elements that can be directly
predicted in SNe models
Kobayashi et al. 2006 (following Timmes et al. 1995)
crucial distinction from n-capture elements: the Fe-peak element productions can actually be predicted theoretically
for some elements, all seems well
Kobayashi et al. 2006(solid line new results
but for others, discomfort
Kobayashi et al. 2006
neutral lines
ionized lines
same predicted Cr abundances
should be simple to do Fe-peak elements:their abundances >> n-capture ones
Fe-peak
light n-cap
heavy n-cap = rare-earth
3rd peak, Thα, etc.
r-process-rich stars give false impression of # of lines in metal-poor abundance
work!
For Fe-peak elements #/species <10 in most cases
The reality is grim for metal-poor turnoff stars
AND, can you believe ANY past analysis??
the outcome for Bergemann et al.?
Comparison of low metallicity spectra in the “visible” spectral region
a new attack: UV STIS spectra
The complex UV spectrum of HD 84937
dotted line, no Fe; solid line, best fit dashed lines: ±0.5 dex from best fit
red line, perfect agreement; other lines, deviations
Why is working in the UV a problem?Opacity competition: metal-poor red giant
Opacity competition: metal-poor turnoff star
A summary of our results on Fe
probable explanation of the abundance “dip”
Other Fe-peak elements: a start
Or, [Co/Fe] ~ +0.3 from both of these neutral and ionized lines
Bergemann 2009: [Co/Fe] = +0.18 (LTE) = +0.66 (NLTE) {probably ~+0.3 (LTE) on our [Fe/H] scale}
This rough cobalt estimate is not too bad …
the red line is the [Co/Fe] trend with [Fe/H] derived by the “first stars” group (Cayrel et al. 2004)
HD 84937
work on Cr I and Cr II is underway
Matt Alvarez, Chris Sneden (UT), Jennifer Sobeck (U Chicago), Betsy den Hartog, Jim Lawler (U Wisconsin)
Summary:
metal-poor stars hold keys to understanding Galactic nucleosynthesis
Atomic physics dictates “non-standard” wavelengths for some elements
STIS in the vacuum UV is the only choice for some poorly understood
element regimes
neutron-capture elements: observers are in the lead!
STIS is crucial for both lightest and heaviest stable elements
Fe-peak elements: theorists are in the lead!
No sane person should believe Fe-peak abundances right now
but STIS data hold promise for the near-future
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